Posters should be smaller than 120 cm x 120 cm (48 inches x 48 inches).

Poster Titles and Abstracts

Maxwell Aifer

UMBC

Thermodynamic Linear Algebra

Linear algebraic primitives are at the core of many modern algorithms in engineering, science, and machine learning. Hence, accelerating these primitives with novel computing hardware would have tremendous economic impact. Quantum computing has been proposed for this purpose, although the resource requirements are far beyond current technological capabilities, so this approach remains long-term in timescale. Here we consider an alternative physics-based computing paradigm based on classical thermodynamics, to provide a near-term approach to accelerating linear algebra. At first sight, thermodynamics and linear algebra seem to be unrelated fields. In this work, we connect solving linear algebra problems to sampling from the thermodynamic equilibrium distribution of a system of coupled harmonic oscillators. We present simple thermodynamic algorithms for (1) solving linear systems of equations, (2) computing matrix inverses, (3) computing matrix determinants, and (4) solving Lyapunov equations. Under reasonable assumptions, we rigorously establish asymptotic speedups for our algorithms, relative to digital methods, that scale linearly in matrix dimension. Our algorithms exploit thermodynamic principles like ergodicity, entropy, and equilibration, highlighting the deep connection between these two seemingly distinct fields, and opening up algebraic applications for thermodynamic computing hardware.

Wynter Alford

University of Rochester

Mesoscopic leads with alternate lead geometries

One approach to fermionic transport in the strongly-coupled regime is the method of Mesoscopic Leads. In this method, the baths are replaced with a series of auxiliary lead modes, each of which is weakly coupled to its own bath. The combined system and lead modes are then treated using weak-coupling approximations. We investigate extending this method to different lead-mode configurations, where some lead modes are coupled to other lead modes, rather than directly to baths. We plan to use this approach to explore whether particular lead mode geometries can more accurately or efficiently model fermionic transport.

Sinan Altinisik

Universität Stuttgart

Validity of quickly driven master equations for the Caldeira-Leggett model

A consistent approximate description of quickly driven quantum systems that are weakly coupled to their environment has been a long-standing goal in the field of open quantum systems. In this work we compare two different master equations, namely the driven Redfield master equation with a pre- and a post-trace rotational wave approximation, for the driven Caldeira-Leggett model without a counterterm against its exact solution. In the weak coupling regime, we find excellent agreement between all three models for slow to medium driving speeds and still reasonable agreement for fast driving speeds. We study the behavior of several system observables and the fidelity of the three models involved and investigate in detail in which parameter regimes the approximations used in the derivation of the two master equations fail. We also compare thermodynamic quantities such as work and heat for the three models and check for thermodynamic consistency.

Tony John George Apollaro

University of Malta

Variational Gibbs State Preparation on NISQ devices

The preparation of an equilibrium thermal state of a quantum many-body system on noisy intermediate-scale (NISQ) devices is an important task in order to extend the range of applications of quantum computation. Faithful Gibbs state preparation would pave the way to investigate protocols such as thermalization and out-of-equilibrium thermodynamics, as well as providing useful resources for quantum algorithms, where sampling from Gibbs states constitutes a key subroutine. We propose a variational quantum algorithm (VQA) to prepare Gibbs states of a quantum many-body system. The novelty of our VQA consists in implementing a parameterized quantum circuit acting on two distinct, yet connected, quantum registers. The VQA evaluates the Helmholtz free energy, where the von Neumann entropy is obtained via post-processing of computational basis measurements on one register, while the Gibbs state is prepared on the other register, via a unitary rotation in the energy basis. Finally, we benchmark our VQA by preparing Gibbs states of the transverse field Ising model and achieve remarkably high fidelities across a broad range of temperatures in statevector simulations. We also assess the performance of the VQA on IBM quantum computers, showcasing its feasibility on current NISQ devices.

Suyash Bajpai

Quantum Biology Laboratory, Howard University

Optimizing slime mold solutions to NP-hard problems using synchronization indices

Despite its simple morphology, Physarum polycephalum – an ancient, multinucleate, single-celled slime mold amoeba – possesses sophisticated information-processing capabilities. Physarum has solved the shortest path problem in complex mazes and demonstrated that it can solve completely or approximately a variety of other optimization problems, including the Boolean satisfiability and traveling salesman problems (TSP). Additionally, it can encode memory of prior periodic stimuli, recapitulating its periodic response when subjected to a similar non-periodic stimulus at much later times. Such intriguing behaviors in nonequilibrium active matter make Physarum a rich playground for exploring the relationship between its intrinsic oscillatory dynamics and the computational complexity of problems it can solve. Exploiting Physarum’s shape-changing dynamics and photoavoidance behavior in custom-fabricated stellate chips with a Hopfield neural network controlling the optical feedback, we have instantiated the TSP for Physarum using N “neuron” lanes for a $\sqrt{N}$-city problem. Earlier works demonstrated that Physarum provides a high-quality solution for non-trivial TSP instances of up to eight cities with approximately linear dependence of computation time on problem size. In contrast, the best approximate classical algorithms (such as the Lin-Kernighan heuristic, simulated annealing, or genetic algorithm) exhibited only a quadratic dependence at best. We aim to verify if this linear scaling of computation time with the problem size extends to larger TSP instances of up to 20 cities. In order to optimize the correlations among the N branches of Physarum, we analyzed an order parameter known as the synchronization index, $S=1⁄N |\sum_{i=1}^N e^{i ϕ_i}|$, where $ϕ_i$ is the individual phase of a branch at a particular time. When there is no synchronization among the branch phases, $S$ is 0. Otherwise, $S$ takes a positive value, reaching maximum phase synchronization when $S$ is 1. We observed higher synchronization indices for shorter tours, suggesting its potential utility as a metric in selecting high-quality TSP solutions. Synchronization indices in the nonequilibrium steady state exhibit prominent peaks when Physarum reaches a solution. To improve the problem-solving efficiency of Physarum, techniques from stochastic resetting and noise-induced transitions will be applied to overcome local energy minima in which the slime mold’s optimization algorithm is trapped, thereby enabling it to find the global minimum via jumps (resets) outside of the local exploratory phase space.

Thales Augusto Barbosa Pinto Silva

Technion

The role of conservation laws on process statistics

In quantum thermodynamics, the statistical predictions of two-time quantities (TTQs), like variation of energy, work, and heat, is crucial for understanding thermodynamic fluctuations. However, measuring and statistically analyzing these process-dependent TTQs in quantum systems poses unique challenges: not only does the measurement disturb these quantities, but also traditional quantum measurements, focused on instantaneous values, do not encompass quantities that depend on an interval of time. To describe TTQ measurements, many protocols were presented in the literature, including the two-point measurement, full-counting statistics, and two-time Heisenberg observables. However, since these forms of defining TTQs statistics and measuring them generally give different predictions and lab results, one might still ask which results are correct and with which laws they are consistent. Our study takes into account these challenges by first proposing criteria for the ideal statistical characterization of TTQs, proposing that they must (i) be state-independent, (ii) adhere to conservation laws, and (iii) satisfy a ‘reality condition’ ensuring known quantities at interval endpoints yield accurate differences. Considering these criteria, we reveal instances where we show that only one protocol can describe TTQs statistics satisfying simultaneously all criteria (i)-(iii): the two-time Heisenberg observables. Finally, we explicitly validate our theory with two compelling examples: a trapped ion platform and a two-qubit system.

Konstantin Beyer

Stevens Institute of Technology

A quantum Jarzynski relation for unknown Hamiltonians

The classical Jarzynski equality establishes an exact relation between the stochastic work performed on a system driven out of thermal equilibrium and the free energy difference in a corresponding quasi static process. This equation not only holds theoretical significance but also bears experimental importance, as it enables the determination of an equilibrium quantity, the free energy difference, through the measurement of externally applied work in a non-equilibrium process.

In the quantum case, the Jarzynski equality only holds if the measurement procedure of the stochastic work is drastically changed and replaced by a so-called two-point measurement (TPM) scheme. Crucially, for an experimenter, such a scheme requires the knowledge of the initial and final Hamiltonian. Since the difference in free energy can be calculated directly from these Hamiltonians, a TPM measurement provides no new insight into this quantity, and the quantum Jarzynski relation has little of the practical significance for which the classical version is known.

Here, we propose a quantum Jarzynski relation that is valid for externally and continuously measured work. In contrast to the TPM scheme, this work measurement is in principle accessible without knowing the system Hamiltonian. Unlike in the classical case, our relation comes in the form of an inequality and therefore only yields bounds to the true free energy difference. The inequality is saturated in the quasiclassical case of commuting initial and final Hamiltonians. Thus, there is a clear quantum disadvantage.

Gianmichele Blasi

Department of Applied Physics, Université de Genève, Geneva 1211, Switzerland

Exact finite-time correlation functions for multi-terminal setups: Connecting theoretical frameworks for quantum transport and thermodynamics

Transport in open quantum systems can be explored through various theoretical frameworks, including the quantum master equation, scattering matrix, and Heisenberg equation of motion. The choice of framework depends on factors such as the presence of interactions, the coupling strength between the system and environment, and whether the focus is on steady-state or transient regimes. Existing literature treats these frameworks independently, lacking a unified perspective. Our work addresses this gap by clarifying the role and status of these approaches using a minimal single-level quantum dot model in a two-terminal setup under voltage and temperature biases. We derive analytical expressions for particle and energy currents and their fluctuations in both steady-state and transient regimes. Exact results from the Heisenberg equation are shown to align with scattering matrix and master equation approaches within their respective validity regimes. Crucially, we establish a protocol for the weak-coupling limit, bridging the applicability of master equations at weak-coupling with Heisenberg or scattering matrix approaches at arbitrary coupling strength.

William F. Braasch Jr.

UMD

Non-Abelian transport distinguishes three usually equivalent notions of entropy production

We extend entropy production to a deeply quantum regime involving noncommuting conserved quantities. Consider a unitary transporting conserved quantities (“charges”) between two systems initialized in thermal states. Three common formulae model the entropy produced. They respectively cast entropy as an extensive thermodynamic variable, as an information-theoretic uncertainty measure, and as a quantifier of irreversibility. Often, the charges are assumed to commute with each other (e.g., energy and particle number). Yet quantum charges can fail to commute. Noncommutation invites generalizations, which we posit and justify, of the three formulae. Charges’ noncommutation, we find, breaks the formulae’s equivalence. Furthermore, different formulae quantify different physical effects of charges’ noncommutation on entropy production. For instance, entropy production can signal contextuality—true nonclassicality—by becoming nonreal. This work opens up stochastic thermodynamics to noncommuting—and so particularly quantum—charges.

Robert Coggins

UMBC

Optimal Driving in Two-Qubit Annealing: The Landau-Zener model

We devise a protocol for more energy-efficient quantum annealing. Quantum-annealing exploits quantum effects to find the best solutions to practical problems in the quest for quantum-supremacy. In problems such as train-scheduling and directing traveling salesmen, good solutions are trivially found, whilst finding the best solutions are NP-hard. Scalability for quantum-annealing is among its greatest barriers to commercial-implementations such as the D-Wave machine. To this end, the dynamics of a two-qubit system, each described by the Landau-Zener model, under a controllable external field is analyzed. The energetic cost involved in the process is quantified by the excess work. The optimal protocol to realize this process is also identified by solving the associated minimization problem.

Jakub Czartowski

Jagiellonian University

We can catalyse it for you thermally: Catalytic transformations for thermal operations

What are the fundamental limits and advantages of using a catalyst to aid thermodynamic transformations between quantum systems? In this work, we answer this question by focusing on transformations between energy-incoherent states under the most general energy-conserving interactions among the system, the catalyst, and a thermal environment. The sole constraint is that the catalyst must return unperturbed and uncorrelated with the other subsystems. More precisely, we first characterise the set of states to which a given initial state can thermodynamically evolve (the catalysable future) or from which it can evolve (the catalysable past) with the help of a strict catalyst. Secondly, we derive lower bounds on the dimensionality required for the existence of catalysts under thermal process, along with bounds on the catalyst’s state preparation. Finally, we quantify the catalytic advantage in terms of the volume of the catalysable future and demonstrate its utility in an exemplary task of generating entanglement using thermal resources.

Gabriella Damas

Phd student at UFG

Exploring Efficiency Dynamics in Quantum Otto Engines under Negative Temperature Conditions

Recent studies show classical and quantum thermal machines operate more efficiently with quasi-static strokes and in environments with negative temperatures. Surprisingly, quantum Otto engines at negative temperatures demonstrate increased efficiency with faster cycles. We investigate this counterintuitive behavior, attributing it to entropy production and friction effects unique to negative temperature environments.

Pedro Vinicius de Castro Portugal

Aalto University

Heat pulses in electron quantum optics

Electron quantum optics aims to realize ideas from the quantum theory of light with the role of photons being played by charge pulses in electronic conductors. Experimentally, the charge pulses are excited by time-dependent voltages, however, one could also generate heat pulses by heating and cooling an electrode [1,2]. Here, we explore this intriguing idea by formulating a Floquet scattering theory of heat pulses in mesoscopic conductors [3]. The adiabatic emission of heat pulses leads to a heat current that in linear response is given by the thermal conductance quantum. However, we also find a high-frequency component, which ensures that the fluctuation-dissipation theorem for heat currents, whose validity has been debated, is fulfilled. The heat pulses are uncharged, and we probe their electron-hole content by evaluating the partition noise in the outputs of a quantum point contact. We also employ a Hong–Ou–Mandel setup to examine if the pulses bunch or antibunch. Finally, to generate an electric current, we use a Mach–Zehnder interferometer that breaks the electron-hole symmetry and thereby enables a thermoelectric effect.

Alexssandre de Oliveira Junior

Technical University of Denmark

Emery Doucet

UMBC

Quantum Darwinism meets Quantum Demons – Emergence of Classical Reality in a Complex Universe

Quantum Darwinism provides a framework to understand how a fundamentally quantum world can support an emergent classical and objective reality. It is however not currently known what properties a general Hamiltonian describing a system interacting with some environment must have to support classicality, only for specific cases such as qubit models. In this talk, I will present our results concerning the criteria necessary for the emergence of quantum Darwinism in a broadly-applicable generic model of an arbitrary finite-dimensional system with a collection of arbitrary finite-dimensional environment degrees of freedom. We consider general two-body system-environment interaction Hamiltonians with or without time dependence. The wide applicability of our results will be a useful tool to guide analyses of quantum-to-classical transitions in a variety of contexts, for instance in minimal models of Maxwell’s demon or other thermodynamic models.

Abdelkader El Makouri

University Mohammed V in Rabat/Laboratory of High Energy Physics: Modeling and Simulation (LHEP-MS)

Quantum unital Otto heat engines: Universal bounds

In the last few decades, with the hope of building quantum computers, a quantum theory of thermodynamics has become a necessity. Quantum computers need to be fueled with systems in highly pure states. To generate these states, one needs to cool quantum systems to very low temperatures. The process of cooling is a thermodynamic process, hence the need for quantum thermodynamics [1]. Furthermore, to my best understanding, quantum computers also need quantum engines, quantum batteries, and quantum clocks. For example, when one wants to do a computation, one will implement a series of unitary gates. These operations need a source of energy, which could be, e.g., a quantum battery. On the other hand, these unitary gates also need good clocks to be implemented with high accuracy. These examples show the importance of this field.

In this poster presentation, I’m going to focus on and present my results on a special type of quantum heat engine called quantum unital Otto heat engines, see Ref. [2]. An example of this engine is when we replace the hot heat bath of the Otto cycle with quantum projective measurement [3,4,5]. I consider a working medium to be an arbitrary qubit. This engine has the property that when there is no monitoring of the working medium, coherence can contribute to heat and work. However, when the system is monitored, in this case, coherence in the energy basis is killed. When the quantum coherence is not erased, I call the engine the undephased engine. On the other hand, when this is not the case I call the engine dephased engine.

For the dephased engine, I show that in the heat engine region, the ratio of work and heat fluctuations is not arbitrary but can be lower and upper-bounded [2,6,7]. The upper bound is unity, and the lower bound is the square of the efficiency of the engine. Furthermore, I also show that the relative fluctuations of work and heat satisfy a hierarchy relationship. These results are shown to hold independently of whether the cycle is time-reversal symmetric or not. The latter refers to the fact that the unitaries characterizing the adiabatic strokes, i.e., $U$ and $V$, need not satisfy $V=U^{\dagger}$.

When we replace the hot heat bath with, e.g., a quantum projective measurement, there are two random quantities that describe the heat released to the cold bath, denoted $Q_{C}$ and $Q_{C}’$. $Q_{C}$($Q_{C}’$) follow from four(five)-point measurements [4,7]. I show that using $Q_{C}$ is better than $Q_{C}’$, either from a computational or physical point of view [8]. This is because $Q_{C}$ needs fewer measurements and satisfies energy conservation not only at the average level but also at the trajectory level. Further, I show that the relative fluctuations of $Q_{C}$ provide a lower bound to the relative fluctuations of the stochastic work $(W)$ and the stochastic heat absorbed $(Q_{M})$. The relative fluctuations of $Q_{C}$ themselves obey a thermodynamic uncertainty relation [9], developed in [10].

When the engine is not monitored, I find that to maintain coherence, one should use Kirkwood-Dirac quasi-probability [11,12,13]. The latter satisfies all the Kolmogorov axioms, except that it can be negative and even a complex number. I give the general expression of the first two cumulants of the thermodynamic quantities for arbitrary unitaries characterizing the adiabatic strokes and arbitrary unital channels [14]. My detailed study gives a comparison between the dephased and undephased engines. The study revealed that when coherence is not erased, the system can work as a heat engine even in the usually-not-allowed regime. My work shows that non-adiabatic transitions are not always harmful and that they can be used advantageously. Furthermore, I show an upper bound on work reliability either for the dephased or undephased engine. My study, I believe, would be important to quantum engines and refrigerators fueled by quantum measurement.

Emily Ferketic

UMBC

Transitionless quantum dynamics in interacting qubits

Driving quantum systems in finite time causes transitions between instantaneous eigenstates. To counteract these often undesirable excitations, shortcuts to adiabaticty have proven themselves to be powerful and effective. In particular, counterdiabatic driving suppresses all excitations away from the adiabatic manifold at all instants. In our work, we apply this strategy to a system of two coupled qubits, in which only one is driven by an external field. This is the simplest example of systems with interacting qubits, which are only locally perturbed.

Dario Ferraro

Università di Genova

Enhancing energy storage crossing quantum phase transitions in an integrable spin quantum battery

We investigate the performance of a one dimensional dimerized XY chain as a quantum battery. Such integrable model shows a rich quantum phase diagram which emerges through a mapping of the spins into auxiliary fermionic degrees of freedom. We consider a charging protocol relying on the double quench of an internal parameter, notably the strength of the dimerization. Within this picture we observe a substantial enhancement of the energy stored per spin as a consequence of driving the system across certain quantum phase transitions.

Moállison Ferreira Cavalcante

UMBC

Nano-welding at minimal dissipation

Recent developments in nanotechnology and nano-electronics necessitate the design of optimal design strategies. For instance, the “welding” of nanowires needs to be facilitated at minimal material strain, or more thermodynamically speaking, at the least amount of dissipation. As a simple example of such nano-welding, we consider two spin-1/2 chains, with open boundary conditions, that are to be joined at one end, thus forming a weak junction. We model the “welding” as the turning-on of a coupling term between the end-points of the spin chains. To analyze the energetics of the process, we calculate the excess or dissipated work. We show that this quantity has a rich scaling behavior depending on which phase the chains are in, for example, it scales as a power-law with a non-integer exponent when both chains are in the critical phase. The optimal control protocol for turning on the coupling term is determined by requiring minimal excess work. It also strongly depends on which phase the chains are in. In particular, when one of the chains is in a gapped phase, the optimal protocol obtained seems to be a general protocol for a gapped many-body system.

Guilherme Fiusa

University of Rochester

Quantum queued collision models

Collision models describe the sequential interactions of a system with independent ancillas. Motivated by recent advances in neutral atom arrays, we investigate a model where the ancillas are governed by a classical controller that allows them to queue up while they wait for their turn to interact with the system. The ancillas can undergo individual open dynamics while they wait, which may cause them to decohere. The system, which plays the role of the server in the queue, can also undergo its own open dynamics whenever it is idle. We first show that this framework generalizes existing approaches for quantum collision models, recovering the deterministic and stochastic formulations in the appropriate limits. Next, we show how the classical queueing dynamics introduces non-trivial effects in the quantum collisions, that can lead to different phases in the system-ancilla response. We illustrate the idea with a model of coherence transfer under noisy waiting dynamics.

Michael Gaida

Universität Siegen

Collision models from the perspective of scattering events

A collision model is a blueprint for generic opensystems in which the environment is modeled as a sequence of ancillas unitarily interacting with the system. It can be viewed as a mathematical idealization of scattering processes in which kinetics are reduced to a mere swichting on and off of the interaction. Such models are capable of describing thermalization processes if one restricts to energy preserving interaction terms, but the link to dynamical scattering models with both internal and motional degrees of freedom remains to be explored. Recently this link has been investigated in a one-dimensional setting [1,2]. Here we consider two and three-dimensional scenarios and study under which conditions they can be described by collision models, once the motional degrees of freedom are averaged out. Specifically, we focus on (non-relativistic) high energy scattering and the energy exchange between internal and kinetic energy. We identify the parameter regimes and interaction types that lead to Gibbsian or non-Gibbsian equilibrium state of the internal degrees of freedom.

[1] S. L. Jacob, M. Esposito, J. M. R. Parrondo, and F. Barra, Quantum scattering as a work source, Quantum 6, 750 (2022). [2] S. L. Jacob, M. Esposito, J. M. Parrondo, and F. Barra, Thermalization induced by quantum scattering, PRX Quantum 2, 020312 (2021).

Safae Gaidi

university Mohamed V in Rabat

Quantum speed limit for non-Markovian dynamics

Quantum speed limits (QSL) are fundamental bounds that quantify the minimum time required for a quantum system to evolve from one state to another. These limits are particularly relevant for understanding and optimizing quantum systems, such as those used in quantum computing and quantum communication. While QSLs have been extensively studied in Markovian (memoryless) environments, their behavior in non-Markovian (memory-dependent) settings presents unique challenges and opportunities. In non-Markovian dynamics, the evolution of a quantum system is influenced by its past interactions with the environment, leading to complex and often richer behaviors. This abstract explores the implications of QSLs for non-Markovian dynamics, examining how memory effects impact the speed of quantum evolution and the tightness of QSL bounds. We review recent theoretical and experimental advances in this area, highlighting the role of different norms and metrics in quantifying QSLs in non-Markovian systems. Understanding QSLs in these environments is essential for developing more efficient and robust quantum technologies.

Shuvadip Ghosh

Indian Institute of Technology Kanpur

True Inverse Current in Quantum Systems

It has recently been demonstrated that inverse current occurs in classical systems, but achieving this in quantum systems remains an intriguing challenge with potential applications in nanoscale thermoelectric generators. In our study, we explore this phenomenon, where a current flows against all thermodynamic forces, including its own conjugate force. We propose a minimal quantum model and conduct detailed analysis to investigate the thermodynamics of the true inverse current, which presents challenges due to its negative contribution to entropy production. Leveraging the Seebeck and Peltier effects, our model serves as an efficient nanoscale thermoelectric heat engine and refrigerator, which are manifestations of the inverse current.

Nikhil Gupt

Indian Institute of Technology Kanpur

Periodically driven quantum thermal transistor

A thermal transistor, regulates the heat flow between two of its terminals in response to the temperature change of a thermal bath coupled to a third terminal. Recent works showed the possibility to realizing the thermal transistor-effect through simple quantum systems which is composed of a quantum system comprising three interacting two level systems, each coupled to a thermal reservoir. This thermal transistor is similar to an electrical bipolar transistor in that thermal currents at the collector and emitter can be controlled by applying thermal current at the base. In contrast, we have proposed a theoretical model in which we demonstrated that periodic control can be used to realize a thermal transistor effect . This periodic modulation allows us to control the heat currents even for fixed bath temperatures. Most importantly, transistor effect in our model persists in the regime, where traditional quantum thermal transistors operating in the absence of periodic modulation, fail to function as viable heat modulation devices. We have also investigated the fluctuation of the heat currents and calculated the noise to signal ratio i.e Fano-factor using the full-counting statistics approach.

Abhaya Hegde

University of Rochester

Time resolving autonomous quantum machines

A typical example of a quantum heat engine is a three-level maser in contact with two thermal baths. The dynamics of such open systems can be viewed within the quantum jump unravelling as a stochastic evolution consisting of a series of quantum jumps occurring at random instants of time. In this presentation we will discuss recent results that employ quantum waiting time distributions, a tool from Full Counting Statistics, to study the heat transfer and entropy production in a quantum heat engine. Waiting times are probability density functions capturing the delay in two subsequent jumps. The heat transfer in three-level maser involves at least two jumps, constituting a cycle, whose statistics are explored in detail by deriving the closed-form expressions for the probability and expected time for cycles. This study allows us to analyze thermodynamic cycles over time, providing insights into the duration required for successful heat transfer cycles.

André Hernandes Alves Malavazi

International Centre for Theory of Quantum Technologies (ICTQT) - University of Gdańsk

Unveiling Detuning Effects for Heat-Current Control in Quantum Thermal Devices

Navigating the intricacies of thermal management at the quantum scale is a challenge in the pursuit of advanced nanoscale technologies. To this extent, theoretical frameworks introducing minimal models mirroring the functionality of electronic current amplifiers and transistors, for instance, have been proposed. Different architectures of the subsystems composing a quantum thermal device can be considered, tacitly bringing drawbacks or advantages if properly engineered.This paper extends the prior research on thermotronics, studying a strongly coupled three-subsystem thermal device with a specific emphasis on a third excited level in the control subsystem. Our setup can be employed as a multipurpose device conditioned on the specific choice of internal parameters: heat switch, rectifier, stabilizer, and amplifier. The exploration of the detuned levels unveils a key role in the performance and working regime of the device. We observe a stable and strong amplification effect persisting over broad ranges of temperature. We conclude that considering a three-level system, as the one directly in contact with the control temperature, boosts output currents and the ability to operate our devices as a switch at various temperatures.

Semih Hüner

University of Stuttgart

Non-equilibrium information exchange in harmonic systems

We investigate the information exchange in coupled harmonic oscillators driven away from equilibrium. We concretely consider the second law of information thermodynamics and evaluate the learning rates for both thermal and mechanical driving in the nonstationary regime for bipartite Markovian systems. We analyze the information transfer as a function of the driving parameters, and show that its direction can be controlled. Further, the aptness and limitations of learning rates as directional information measures is addressed.

Nobumasa Ishida

University of Tokyo

Demonstrating Thermodynamic Trade-Off Relations Using a Quantum Computer

Quantum thermodynamic trade-off relations are critical for understanding the fundamental limitations and costs associated with quantum information processing. Despite extensive theoretical work, experimental validations of these trade-offs remain scarce. This study bridges that gap by leveraging the capabilities of quantum computers to empirically test these relations. We derive a generalized quantum thermodynamic uncertainty relation that establishes a cost-precision trade-off for observables in any quantum system governed by trace-preserving completely positive maps. By utilizing the broad applicability of our derived bound, we experimentally verify this trade-off relation using a superconducting quantum processor. Our findings reveal that the thermodynamic cost imposes strict constraints on the achievable precision of observables. Our results pave the way for using quantum computers to test theories of quantum thermodynamics and study the thermodynamics of the computers.

Clemens Jakubec

University of Arizona

Quantum Fluctuation Forces between Optically Trapped Nanospheres

We present an analysis of the quantum fluctuation forces between two dielectric nanospheres trapped via optical tweezers. We develop a full quantum description of the radiative forces between the two nanospheres using a open quantum system master equation approach. Considering their mutual interaction mediated via the classical trapping field and the quantum fluctuations of the electromagnetic field, an analysis of the three separate contributions to the total potential – the Casimir-Polder potential, the classical trap potential and the optical binding potential – is presented. The total potential is subsequently studied as a function of various parameters, such as the tweezer field intensity and phase, demonstrating that, for appropriate sets of parameters, there exists a mutual bound state of the two nanospheres which can be 1000 K deep. Furthermore, we utilize the master equation approach to study the decoherence and dissipation of the quantized centre of mass of the nanospheres, focusing in particular on the interplay between fluctuation fields and the external drive. Our results are pertinent to ongoing experiments with trapped nanospheres in the macroscopic quantum regime and for exploring quantum thermodynamic phenomena.

Siddharth Jindal

University of Houston

Generalized Free Cumulants for Quantum Chaotic Systems

The eigenstate thermalization hypothesis (ETH), the leading conjecture for the emergence of statistical mechanics in quantum systems, is formulated in terms of matrix elements of observables. However, much stronger statements about chaotic systems are available from the structure of their eigenstates. Motivated by the connection between the ETH and free probability theory, we develop a diagrammatic formalism for computing eigenstate correlations. With our formalism, we shed light on chaotic dynamics, including thermalization and entanglement, in isolated quantum chaotic systems.

Mao Kaneyasu

The University of Tokyo

Analyzing distribution of quantum resource under random noise

Quantumness can be regarded as a resource available for various tasks. To realize the large-scale quantum information processing, it is essential to utilize such resources even under noisy environments. This research explores the effect the random noise gives to the quantum resource. We formalize the noisy channel using an ancillary system and a random unitary. The probability distribution of quantum coherence after passing through the random channel is derived based on the random matrix theory, and the distribution is verified by the numerical experiments.

Anthony Kiely

University College Dublin

Universally Robust Quantum Control

We study the robustness of the evolution of a quantum system against small uncontrolled variations in parameters in the Hamiltonian. We show that the fidelity susceptibility, which quantifies the perturbative error to leading order, can be expressed in superoperator form and use this to derive control pulses which are robust to any class of systematic unknown errors. The proposed optimal control protocol is equivalent to searching for a sequence of unitaries that mimics the first-order moments of the Haar distribution, i.e. it constitutes a 1-design. We highlight the power of our results for error resistant single- and two-qubit gates.

Reference: Phys. Rev. Lett. 132, 193801 (2024)

Henning Kirchberg

Chalmers University of Technology

Maxwell Demon revisited: a microscopic protocol for quantum measurement, information gain, work extraction and & energetic cost

In many applications, the process of information gain is discussed without considering the time and energy cost required to obtain information, with the assumption that the Maxwell Demon can acquire information instantaneously at no additional energy cost except from memory erasure to a heat bath. This work addresses these issues. We examine a two-level system interacting with a (quantum) free particle as a meter. We employ the two-step Von-Neumann measurement protocol to analyze two aspects separately: (i) the evolution of the coupled system and meter and the entanglement between them considered as functions of the coupling and its duration, and the information gained during this process, and (ii) the fundamental energetic cost for coupling and decoupling the system and meter. This makes it possible to consider the energetic cost of acquiring information. Additionally, by including photon-induced stimulated emission in the protocol we investigate the information-driven work extraction from the measured system. Our analysis focuses on the ratio between the work generated from the obtained information and the energy invested to acquire it, as well as the power output (energy per measurement duration) and its optimization.

Sanah Rahman Kokkarani

Indian Institute of Space Science and Technology

Effect of DM interaction in the charging process of a Heisenberg spin chain quantum battery

We investigate the charging performance of an anisotropic XYZ model of Heisenberg Spin Chain Quantum Battery (HS QB) along with different components (X, Y and Z) of Dzyaloshinskii-Moriya Interaction (DMI) for three cases - short range, long range and infinite range interactions. We find that the presence of DMI enhances the charging power and total stored energy of the QB compared to HS QB in most of the cases, by considering both local charging (interacting case) and collective charging protocols. The largest enhancement in total stored energy and corresponding average power is achieved in the case of long range and infinite range interactions. The maximum charging power increases as the number of spins(N) increases, approaching a scaling exponent alpha=1.846 for collective charging of HS QB with Y component of DMI under infinite range interactions. Also the maximum stored energy enhances linearly with the number of spins.

Ankit Kumar

University of Gdansk

Unbiased Current Pumping with a SQUID

It was experimentally observed by Giazotto et al. [Nat. Phys. 7, 857 (2011)] that, with the help of an externally applied magnetic flux, an unbiased current is induced in an InAs wire embedded in a Superconducting Quantum Interference Device (SQUID). We explain such a quantum pumping by describing the Cooper pairs in SQUID terminals as a bosonic open quantum system governed by the Markovian master equation. The magnetic flux breaks the bidirectional tunnelling symmetry between different superconducting islands, which eventually leads to pumping in an external circuit coupled to the device. We also discuss the subtle importance of the nonlinear Coulomb repulsion between different terminals and demonstrate how it restricts the otherwise unconstrained magnitude of the pumped current.

Aleksander Lasek

UMD

Testing the non-Abelian eigenstate thermalization hypothesis

The eigenstate thermalization hypothesis (ETH) explains why isolated quantum systems thermalize internally. Conserved quantities, or “charges,” complicate matters. One can apply the ETH, and infer about thermalization, in a subspace where all the charges have well-defined values. But such a subspace might not exist if the charges do not commute with each other. Does thermalization still occur? Additionally, noncommuting charges engender energy degeneracies that might prevent thermalization. These issues have started being addressed only recently, as the ETH was modified to a non-Abelian ETH. Introducing charge noncommutation into a seminal thermodynamic result, the non-Abelian ETH is a truly quantum-thermodynamic phenomenon [1]. We present the first comprehensive numerical support for the non-Abelian ETH. We model a one-dimensional qubit chain governed by the Heisenberg Hamiltonian, whose charges (the total spin components) entail SU(2) symmetry. We discover analytically and numerically that noncommuting charges introduce an unexpected factor into the non-Abelian ETH. The factor depends on the symmetry group’s Casimir operator and enables the non-Abelian ETH’s self-consistency. Away from the thermodynamic limit, this factor may affect deviations from thermodynamic behaviors.

[1] Majidy, Braasch, Lasek, Upadhyaya, Kalev, and Yunger Halpern, ‘‘Noncommuting conserved charges in quantum thermodynamics and beyond’’, Nat Rev Phys 5, 689–698 (2023)

Maximilian Lock

Atominstitut, TU Wien

The emergence of the second law of thermodynamics in isolated quantum systems

According to the second law of thermodynamics, the entropy of an isolated system increases over time. Isolated quantum systems, however, evolve unitarily, and therefore the von Neumann entropy is constant. While it is known that certain observables appear to equilibrate (on average) in an isolated quantum system, the question remains open: in what sense does the entropy of an isolated quantum system increase over time?

The conflict between reversible microscopic, and irreversible macroscopic behaviour in classical systems (the so-called Loschmidt paradox) has been solved using notions of coarse-graining, and an interpretation of thermodynamic laws as averages. We extend this analysis to isolated quantum systems, building upon the theory of equilibration-on-average to investigate entropies that are defined with respect to observables and recover a variant of the second law – the entropy (relative to an equilibrating observable) for isolated quantum systems tends towards its equilibrium value. Entropy fluctuations appear as shadows of the underlying reversible evolution, decreasing in magnitude as the system-size increases, and the second law of thermodynamics emerges. We find that this irreversibiliy doesn’t require the kind of coarse-graining suggested by von Neumann, later formalised into the so-called observational entropy. We illustrate our analytic results by applying them to simulations of dynamics in the Ising model.

Ivana Lucena

UFPB

Thermodynamic uncertainty relations in mesoscopic devices

Thermodynamic uncertainty relations in mesoscopic devices

Jinghao Lyu

University of California, Davis

Efficient Quantum Work Reservoirs at the Nanoscale

When reformulated as a resource theory, thermodynamics can analyze system behaviors in the single-shot regime. In this, the work required to implement state transitions is bounded by $\alpha$-Renyi divergences and so differs in identifying efficient operations compared to stochastic thermodynamics. Thus, a detailed understanding of the difference between stochastic thermodynamics and resource-theoretic thermodynamics is needed. To this end, we study reversibility in the single-shot regime, generalizing the two-level work reservoirs used there to multi-level work reservoirs. This achieves reversibility in any transition in the single-shot regime. Building on this, we systematically explore multi-level work reservoirs in the nondissipation regime with and without catalysts. The resource-theoretic results show that two-level work reservoirs undershoot Landauer’s bound, misleadingly implying energy dissipation during computation. In contrast, we demonstrate that multi-level work reservoirs achieve Landauer’s bound and produce zero entropy.

José Antonio Marín Guzmán

University of Maryland, College Park

Criteria for useful autonomous quantum-thermodynamic machines

Quantum thermodynamicists have been designing quantum machines for decades, and experimentalists have realized such machines recently. Examples include engines, refrigerators, clocks, and batteries. These machines offer fundamental insights but are impractical: running the devices usually requires substantial control and energy. Autonomous quantum machines offer hope for practicality. They operate without time-dependent external control, extracting free energy from, e.g., temperature gradients in their environments. Autonomous quantum refrigerators have recently been realized with trapped ions and superconducting qubits, and one was competitive with previous state-of-the-art cooling protocols. Motivated by the recent surge in autonomous quantum machines, we propose to give the subfield direction. In the spirit of making quantum thermodynamics practical, we posit criteria analogous to DiVincenzo’s criteria for quantum computing. We expect these criteria to be necessary for realizing useful autonomous quantum machines. We illustrate the criteria with diverse machines and diverse platforms (Rydberg atoms, superconducting qubits, trapped ions, molecules, etc.). The criteria are intended to foment and guide the development of useful quantum thermal machines.

Reference: Marín Guzmán, Erker, Gasparinetti, Huber, and Yunger Halpern, arXiv:2307.08739 (2023).

Paweł Mazurek

University of Gdansk

Nonreciprocal Quantum Batteries

Nonreciprocity, arising from the breaking of time-reversal symmetry, has become a fundamental tool in diverse quantum technology applications. It enables directional flow of signals and efficient noise suppression, constituting a key element in the architecture of current quantum information and computing systems. We explore its potential in optimizing the charging dynamics of a quantum battery. By introducing nonreciprocity through reservoir engineering during the charging process, we induce a directed energy flow from the quantum charger to the battery, resulting in a substantial increase in energy accumulation. Despite local dissipation, the nonreciprocal approach demonstrates a fourfold increase in battery energy compared to conventional charger-battery systems. This effect is observed in the stationary limit and remains applicable even in overdamped coupling regimes, eliminating the need for precise temporal control over evolution parameters. Our result can be extended to a chiral network of quantum nodes, serving as a multi-cell quantum battery system to enhance storage capacity. The proposed approach is straightforward to implement using current state-of-the-art quantum circuits, both in photonics and superconducting quantum systems. In a broader context, the concept of nonreciprocal charging has significant implications for sensing, energy capture, and storage technologies or studying quantum thermodynamics.

Paul Menczel

RIKEN

Unravelings of time-local quantum master equations

The quantum jump method provides access to both the theoretical analysis and the numerical simulation of fluctuating variables in transport processes. It originally applies to processes that can be described by a quantum master equation in Lindblad form. When studying strong coupling or non-Markovian effects, one often encounters time-local quantum master equations that deviate from the Lindblad form. Here, we compare approaches that extend the quantum jump method to such master equations. We discuss the numerical stability of these approaches and whether their quantum jump trajectories can be related to the fluctuations of the physical system. We demonstrate our findings by the example of the pseudomode framework, where the dynamics of the Caldeira-Leggett model is reproduced by a non-positive master equation, and derive the optimal quantum jump unraveling in this scenario.

Jonathan Miller

UMBC

Quantum Information Scrambling in nonlinearly coupled oscillators

In its modern phrasing, quantum chaos refers to the exponentially fast scrambling of information through quantum many-body systems. A natural question arises: does this notion also apply to less complex scenarios? To this end, we explore nonlinear scrambling of quantum information in a family of models of two-coupled harmonic oscillators. In particular, we numerically explore signatures of quantum chaos in these models using the Out-of-Time-Ordered Correlator. Our results exhibit the early time exponential increase of this correlation function, from which we can deduce the quantum Lyapunov exponents that characterize quantum chaos in these models.

Nathan Myers

Virginia Tech

Unifying Collisional Models and the Monte Carlo Metropolis Method: Algorithms for Dynamics of Open Quantum Systems

Classical systems placed in contact with a thermal bath will inevitably equilibrate to a thermal state at the bath temperature. The same is not generally true for open quantum systems, which place additional conditions on the structure of the bath and system-bath interaction if thermalization is to occur. Collisional models, or repeated interaction schemes, are a category of microscopic open quantum system models that have seen growing use in studying quantum thermalization, in which the bath is modeled as a large ensemble of identical ancilla systems that sequentially interact with the system. We demonstrate that, when each bath ancilla is prepared in a thermal state with a discrete spectrum that matches the energy eigenstate transitions of the system, the system dynamics generated by the collisional model framework are identical to those generated under the Metropolis algorithm. This equivalence holds not just in the steady state regime, but also in the transient regime. As the Metropolis scheme does not require explicitly modeling the system-bath interaction, this allows it to be used as a computationally efficient alternative for simulating collisional model dynamics.

Carlos Neto

Federal University of Paraíba

Investigation of Landauer’s principle in a qubit erasure protocol at finite temperature

More than sixty years ago, Landauer’s principle demonstrated a fundamental link between information theory and classical thermodynamics. The principle states that any irreversible informational process that occurs in a system is inevitably accompanied by the dissipation of heat into the environment. The principle was experimentally verified in the last decade with many different systems, including a trapped colloidal particle, a single atom, and a micromechanical oscillator. However, an absolute quantum version of the idea is still under debate and has attracted researchers from many different areas. Specifically, we have witnessed a renewed interest in this topic since the recent emergence of the area of quantum thermodynamics. In the present work, we propose a quantum information erasure protocol and analyze its implications in light of Landauer’s principle. The protocol relies on the use of the degeneracy in the degrees of freedom of a structured qubit-like reservoir to erase a given information stored in a qubit memory. In this perspective, we can explicitly calculate the change in the von Neumann entropy of the system, along with the heat dissipated to the degrees of freedom of the environment. Also, we provide an experimental testbed for the protocol based on an all-optical circuit with only linear optical devices. In this case, the polarization degree of freedom encodes the information to be erased in the memory, and the path degree of freedom plays the role of the reservoir. Likewise, a quantum circuit model is provided so that the steps of the erasure can be reproduced in other quantum platforms. As such, the model provides a simple and practical architecture for the realization of tests of the Landauer principle in a quantum-mechanical scenario.

Maicol Ochoa

University of Maryland CP

Quantum thermodynamics of lossy polaritons under time-periodic driving

Exciton polaritons are hybrid light-matter states with unique properties modified by their coupling strength, relaxation rates, and external forces. These systems are, therefore, interesting for investigating hybrid state formation and quantum control and for their potential impact on modern quantum information technologies and materials. This work presents a dynamic and thermodynamic model for lossy polaritons under periodic-in-time driving, obtaining the polariton’s density-matrix quantum master equation and deriving the dissipative time propagator. We analyze the stationary state for this system in terms of the coupling strength, damping rates, anharmonicity, and driving force and frequency by characterizing the maximum power, irreversible heat, and overall thermodynamic efficiency. We also investigate how exciton-phonon entanglement, polariton coherence, and spectral density determine the thermodynamic properties of the system. The results of our investigations indicate that strong coupling and anharmonicity are detrimental to the total energy stored in the polariton, while they may have a positive impact on the off-resonance performance of the process. We also find that exciton saturation and interference can limit the polariton’s total energy. Moreover, we find a rapid increase in the system entanglement with coupling strength, but this maximum shifts from the point of maximum energy absorption upon driving.

Hamza Patwa

Quantum Biology Laboratory, Howard University

Single-photon superradiance in cylindrically symmetric collectives of two-level systems at thermal equilibrium

Single-photon superradiance is a coherent phenomenon that results from many identical quantum systems absorbing and/or emitting single photons collectively at a higher rate (\Gamma_j) than any one system can individually (\gamma). This phenomenon has been studied analytically in idealized continuous distributions of two-level systems (TLSs), as well as numerically in photosynthetic nanotubes and cytoskeletal architectures. Modeling the tryptophan molecule—an aromatic amino acid strongly fluorescent in the ultraviolet—as a TLS, we numerically analyze a variety of tryptophan network architectures with different transition dipole moment geometries by diagonalizing a non-Hermitian effective Hamiltonian derived from a Lindblad master equation, describing the interaction of the network with the electromagnetic field. This Hamiltonian has complex eigenvalues, which give us the energies or Lamb shifts (real part) and decay rates (imaginary part) of the collective system. For cylindrically symmetric architectures of such transition dipole moments, we observe the existence of bright superradiant states (i.e., with large decay rates \Gamma_j » \gamma). Specifically, for an architecture consisting of identical rings of TLSs equally spaced along the z-axis, transition dipoles oriented parallel to the z-axis (parallel dipole, or PD, arrangement) give rise to superradiant states in the high-energy portion of the spectrum. The brightest superradiant state in this case has a collective decay rate over 2000\gamma. However, if the dipoles are oriented in the x-y plane tangent to the ring (tangent dipole, or TD, arrangement), the superradiant states are not even half as bright (the brightest superradiant state having a collective decay rate of less than 1000\gamma), but they are in the low-energy portion of the spectrum. In the thermal Gibbs ensemble, a spectrum with smaller decay rates would not necessarily have a smaller thermal average than a spectrum with large decay rates, since each decay rate is weighted by a Boltzmann factor that depends on the negative of the energy. Thus, decay rates at lower energies have higher Boltzmann factors, which can still lead to a high thermal average. High thermal averages imply that those transition dipole geometries would be favorable for cylindrically symmetric biological structures to optimize superradiant effects for certain observables while in equilibrium with a thermal bath. To test this, we analyzed several biological structures with tryptophan networks of this kind (microtubules, actin filaments, and amyloid fibrils), and we indeed find that the thermal average of the quantum yield—defined as the ratio of the thermal average of the radiative decay rate to the sum of the thermal averages of the radiative decay rate and the non-radiative decay rate—only dampens by ~3-5% when thermal noise increases from zero to five times that of room temperature. The TD and PD cases show the extremal cases of how cylindrical transition dipole geometries affect the superradiant states and their thermal average, and provide insight into how biological systems may exploit these properties. Cycles of nonequilibrium pumping and thermalization in such tryptophan mega-networks could play a pivotal role in operating quantum thermodynamic engines in cellular environments, as we begin to track the evolution of von Neumann entropy in these structures over time.

Kacper Prech

University of Basel

Quantum Thermodynamics of Continuous Measurement and Feedback

Quantum coherence plays an important role in thermodynamics of quantum systems, in particular under measurement and feedback. Recently, a novel Quantum Fokker Planck Master Equation (QFPME) has been derived for systems under continuous measurement and feedback [1]. This formalism captures the joint time-evolution of a system and a detector with finite bandwidth. Starting from the QFPME, we derive expressions for work, heat, and measurement-induced energy changes, providing insight into the thermodynamics of continuous feedback protocols under finite bandwidth. We illustrate our results on a feedback-controlled coherently driven qubit, which implements a continuous version of a discrete measurement-driven engine [2]. Our work provides a novel approach to investigating the thermodynamics of continuously measured and controlled quantum systems under experimentally relevant circumstances.

Eugenia Pyurbeeva

Hebrew University of Jerusalem

Direct entropy measurements in electronic nanodevices

Entropy has a unique role amongst thermodynamic variables in the connection it provides between the macroscopic averaged quantities, such as volume, temperature, or magnetisation, and microscopic dynamics. This connection is particularly informative and powerful in small systems with few degrees of freedom, in which the value of entropy allows one to deduce their internal dynamics, such as energy level structures and degeneracies, number of localisation sites and quantum effects. However, as the size of a system decreases, the standard approach to measuring entropy, based on heat flows and its thermodynamic definition dS=dQ/T, becomes progressively more unfeasible, as it requires measuring microscopic heat flows. In order to solve this problem, in recent years several alternative methods have been proposed for measuring entropy in nanodevices, utilising electrical measurements: those of charge state[1] or charge transport[2,3]. The entropy measurement approach — finding the absolute values of entropy differences between the charge states and deducing the dynamics from them, offers a novel and powerful tool of exploring quantum states and has been used in a wide variety of nanoscale systems[3-6], from single molecules to exotic quasiparticles. We give a overview of electronic entropy measurement methods from a theoretical viewpoint and show that they can be incorporated within a single thermodynamic framework for treating nanoscale systems exchanging particles with thermal baths[7], as well as a brief report on the current state of experiments in the field[8]. Direct electronic measurements of thermodynamic parameters offer a pathway to harnessing the well-developed experimental techniques of nanoelectronics for studying quantum thermodynamics. Molecular devices have the potential to be pivotal for this application, due to the endless possibilities of engineering their qualities to enhance particular effects, such as entanglement, high spin values, multiple localisation points, interference paths, or electron-mechanical coupling. Finally, we discuss our plans for the future, as well as open questions standing in the path of its realisation.

Harini Radhakrishnan

University of Tennessee-Knoxville

The Two Body Density Matrix of a Luttinger Liquid

The n-body reduced density matrix (n-RDM) characterizes higher order correlations in an interacting many-body system. This quantity can be used to compute any n-body observable without direct access to the full wavefunction, and is experimentally measurable. Analytically, the problem of computing higher order density matrices becomes increasingly challenging as the number of local operators grows. However, within the Tomonaga Luttinger liquid regime, bosonization provides access to correlation functions by representing them as exponentials of bosonic field operators that are analytically tractable, even in finite size systems. We outline the derivation of the exact 2-RDM from bosonization and map to the J-V model of interacting, spinless fermions in one dimension, where the low-energy sector is describable by Tomonaga Luttinger liquid theory. Finally, we demonstrate the use of our result by computing observables such as the lattice energy, structure factor, and n-particle entanglement.

Rohit Kishan Ray

Institute for Basic Science

No-signaling and the Fourth Law of Thermodynamics

The steepest entropy ascent (SEA) formalism, which describes the evolution of an out-of-equilibrium system using local entropy production maximization ansatz, has been recently dubbed as the fourth law of thermodynamics (FLT). It has found application in many systems of interest which include but are not limited to quantum devices, superconducting systems, quantum algorithms, chemical kinematics and so on. One unique feature of this formalism lies in the fact that it is highly nonlinear. Thus, a valid question raises, whether in there is a supraluminal communication (signaling) between two non-interacting parts of a composite in such a theory. As ample literature exists to hint at a positive response to the above question, we show that the non-linearity in SEA/FLT does not pose the signaling problem. In the process, we also broaden the definition of signaling. This result in itself provides a theoretical validity to the plethora of new research involving many-body interactions under SEA.

Tom Rivlin

TU Wien

Equilibration of objective observables in a dynamical model of quantum measurements

The challenge of understanding quantum measurement persists as a fundamental issue in modern physics. Particularly, the abrupt and energy-non-conserving collapse of the wave function appears to contradict classical thermodynamic laws. The contradiction can be resolved by considering measurement itself to be an entropy-increasing process, driven by the second law of thermodynamics. A recent proposal on this theme, dubbed the Measurement-Equilibration Hypothesis, builds on the Quantum Darwinism framework derived to explain the emergence of the classical world, asserting that measurement outcomes emerge objectively from unitary dynamics via closed-system equilibration. In this talk, I will introduce the set of objectifying observables that best objectively encode the measurement statistics of a system in this hypothesis. I will also show results quantifying the probability that an observer will obtain an incorrect measurement outcome, and that objectifying observables readily equilibrate on average for a reasonable class of Hamiltonians. Numerical results will also be presented showing that the error only approaches zero with increasing environment size when the environment is coarse-grained into so-called observer systems, suggesting that coarse-graining is required for the emergence of objectivity.

Reece Robertson

UMBC

Performance of Simon’s algorithm in the NISQ era

Simon’s algorithm was one of the first to demonstrate a divergence in complexity between the quantum and classical computational paradigms. The algorithm, however, assumes access to noise-free qubits—a dream which has not yet been realized. In our work we use Simon’s algorithm to benchmark the error rates of devices currently available in the ““quantum cloud””. As a main result we obtain an objective comparison between the different physical platforms. It is observed that the error scales linearly on IonQ trapped ion computers, while IBM superconducting computers experience a superlinear jump in error at the 8-12 qubit range. However, all computers show significant error (≥ 25%) at large scales. This indicates the extent of improvement needed in quantum hardware and error mitigation before algorithms like Simon’s can be run with advantage at large scales.

Alberto Rosal

University of Rochester

Quantum Speed Limits Based on Schatten Norms: Universality and Tightness

We present two families of quantum speed limits (QSLs) for finite-dimensional quantum systems undergoing a general physical process. These QSLs were obtained using Schatten α-norms, firstly exploiting the geometric features of the space of quantum states, and secondly employing the Holder’s inequality for matrix norms. In particular, for the case of single-qubit states, we find that the geometric QSL is independent of the Schatten norm chosen, thus revealing a universality behavior of such quantifiers. Furthermore, we provide a comparison of these quantum speed limits with existing paradigmatic QSLs in literature, thus showing that the latter results represent particular cases of a general class of QSLs related to Schatten α-norms. Noteworthy, we address necessary and sufficient conditions for the tightness of the quantum speed limit that mostly depends on the populations and quantum coherences of the evolved single-qubit state, and also present a geometric interpretation for these set of conditions. Finally, we compare the two QSL obtained for the dynamics of single-qubit states, also presenting an inequality between them that has a clear geometrical meaning.

Dominik Šafránek

Institute for Basic Science

Work Extraction from unknown quantum sources

The usual notion of how much can be extracted from a quantum system is based on ergotropy, which requires full knowledge of the initial state. However, to know that one either has to perform a full quantum tomography, which is nearly impossible to do on large quantum systems, or to create the state itself, which consumes at least as much energy than can be extracted. This seems as highly impractical, especially when the source is externally given to us. We show how to extract energy from unknown states, that we characterized only by a single, coarse measurement, thus circumventing the need to perform a full quantum tomography.

Rishav Sagar

University of Gdansk

Boosting Microscopic Refrigeration with Catalysts

We consider a two stroke refrigerator in the microscopic regime. The refrigerator is modelled in two discrete strokes to take out heat from cold bath by using the provided work. We introduce an additional auxilliary system called catalyst such that the state of the catalyst remains unchanged after the completion of a thermodynamic cycle. By setting up a well-defined thermodynamic framework, we can demonstrate the enhancement in coefficient of performance gained by introducing a catalyst. We then propose applications of introducing catalysts in thermal machines and explore their potential impact on upcoming quantum technologies.

Tanmay Saha

The Institute of Mathematical Sciences

Quantum homogenization in non-Markovian collisional model

Collisional models are a category of microscopic framework designed to study open quantum systems. The framework involves a system sequentially interacting with a bath comprised of identically prepared units. In this regard, quantum homogenization is a process where the system state approaches the identically prepared state of bath unit in the asymptotic limit. Here, we study the homogenization process for a single qubit in the non-Markovian collisional model framework generated via additional bath-bath interaction. With partial swap operation as both system-bath and bath-bath unitary, we numerically demonstrate that homogenization is achieved irrespective of the initial states of the system or bath units. This is reminiscent of the Markovian scenario, where partial swap is the unique operation for a universal quantum homogenizer. On the other hand, we observe that the rate of homogenization is slower than its Markovian counter part. Interestingly, a different choice of bath-bath unitary speeds up the homogenization process but loses the universality, being dependent on the initial states of the bath units.

Kiera Salice

University of Houston

On the Origin of Classicality: Robust Quantification and Experimental Verification of Quantum Darwinism

Quantum Darwinism is a physical framework that explains the emergence of our classical experience from the quantum substrate. In this poster, we outline a comprehensive experimental implementation of the foundational ideas of Quantum Darwinism including the emergence of branching structures and the emergence of classicality through information-theoretic quantities such as, the mutual information, quantum discord and the Holevo quantity. Additionally, we propose a class of local observables as a novel quantifier for probing quantum-to-classical transitions. This quantity constitutes an experimentally efficient method of observing the emergence of classicality. We provide both a mathematical proof and experimental verification for this quantity. This work further positions Quantum Darwinism as a leading theory in addressing the elusive quantum-to-classical transition.

Pratik Sathe

Los Alamos National Laboratory

Operator based quantum thermodynamic uncertainty relations

The Heisenberg uncertainty principle links the uncertainties of the position and momentum of a particle, and it has an important footprint on the quantum behavior of a physical system. Motivated by this principle, we propose that thermodynamic currents associated with work, heat, and internal energy are described by well-defined Hermitian operators or observables. First, we show that, in principle, it is possible to perform single-point measurements to compute their average rates.These rates or currents differ from their classical counterparts due to the non-commutativity of the corresponding operators. Using the Robertson-Schr\odinger uncertainty relations, we then obtain various thermodynamic uncertainty relationships between them. In particular, we connect the fluctuations in heat rate and thermodynamic power with those in internal energy. We further illustrate this approach by applying it to quantum batteries, where we derive an energy-power uncertainty relationship and show how measurements affect the fluctuations.

Lodovico Scarpa

University of Oxford

Observable Thermalization in Isolated Quantum Systems

I will present my research on the thermalization of observables in isolated quantum systems. Progress in this field is essential to understanding the emergence of irreversibility from the underlying unitary dynamics, as well as to determine the applicability and limitations of thermodynamics and statistical mechanics. Together with my collaborators, I have been developing a new approach called “Observable Thermalization”, which is based on a maximum entropy principle. This framework has already led to genuinely novel predictions, including in Many-Body Localized systems. Moreover, we have been able to use it to determine the equilibrium value (diagonal ensemble) of observables without the need to know the energy eigenstates. We found strong numerical support for the framework’s predictions for one-body and two-body observables in 7 different spin-1/2 XYZ-type 1D Hamiltonians (covering integrable to quantum chaotic) for 5 different initial states and with system sizes up to L=20. In particular, we are able to predict the equilibrium value of the whole eigenvalue probability distribution of one and two-body observables with a remarkable degree of accuracy. For one-body observables, the distance between the exact and predicted distributions is always less than $10^{-9}$, while for two-body observables it is less than $10^{-3}$ in 90% of cases. Our results mark significant progress towards a fully predictive theory of thermalization in isolated quantum systems and open interesting questions about observable-specific thermodynamic quantities.

Annie Schwartz

University of Rochester

Effects of Dispersive Time Dependent Drives in Superconducting Circuits

Dispersive interactions between systems far from resonance with each other play a key role in superconducting circuits. Notwithstanding, various aspects still remain largely unexplored, particularly concerning the interplay between dispersive and time-dependent driven dynamics. In this poster we discuss our ongoing study of indirect time-dependent driving through dispersive media. We show how a dispersive resonator acts as a filter, both damping the overall intensity of a time-dependent drive and introducing additional tones at different frequencies. We will then use this to provide realistic guidelines on how to design perfect Rabi oscillations in superconducting circuits via indirect drive, taking into account dispersive and AC Stark shifts.

Tingzhang Shi

Peking University

Negative Excess Work Anomaly and 1/N Absence of the Anomaly

Consider a piston system undergoing an adiabatic compressing process. For a canonical ensemble, if the driving speed is finite, the adiabatic work done during the compression is always larger than that of a quasi-static process. However, the excess work could be negative for a micro-canonical initial state. In this work, we study the micro-canonical excess work distribution of three different piston systems: classical non-relativistic piston, classical relativistic system, and quantum non-relativistic piston. We find that the excess work could be negative for the micro-canonical initial state, which is an anomaly. Moreover, we observe a 1/N absence of anomaly in the classical piston system: when compressing the length of the container to 1/N times the initial length, the negative excess work anomaly disappears. The integer phenomenon in a classical system is quite interesting. This 1/N phenomenon is recovered in the low-speed limit of the relativistic piston system. However, it disappears in the quantum piston systems.

Joseph Smiga

University of Rochester

Quantifying information in measurement back-action

Oftentimes, experiments will take multiple measurements of a system with the assumption that it resets each time. This is not done because it is reflective of the real world, but because it often makes calculations more manageable. This is a particular problem for quantum systems in which measurement back-action plays a major role in the dynamics of the system. This work considers the case in which the system is not reset between measurements. We develop various calculable information-theoretic measures to understand the effects of correlations between repeated measurements and observations. Examples are used to illustrate these methods.

Jeongrak Son

Nanyang Technological University

A hierarchy of thermal processes collapses under catalysis

With the advent of quantum technology, there has been significant growth in the need to understand the performance of quantum devices when they operate in a thermal environment. A systematic approach for studying devices in such settings is to consider the maximal set of operations that are feasible under thermodynamic constraints and other practical limitations. If only energy preservation is imposed, this maximal set of operations is defined as the thermal operations. Due to their all-encompassing characterization, thermal operations are particularly effective in establishing the fundamental limits of thermodynamic performances. The flip side of this generality is the difficulty of directly implementing some of the allowed operations. Hence, the study of simpler subclasses of thermal operations has been proposed, mostly motivated by the ubiquitous presence of specific operations, such as the Jaynes-Cummings interaction. It is hoped, then, that mixing and combining such mainstream operations might allow recovery of the full processing power characterized by thermal operations. This optimism was initially inspired by the concept of universality in quantum computation, where it is known that smaller gate sets (such as 2-local gates) can indeed decompose any difficult global operations. However, the existence of a strict hierarchy between thermal operations and simpler operations is found. After this inability to fully emulate thermal operations became known, further studies on simpler operations lost some of its momentum and remain relatively understudied.

In this work, we report an unexpected method that fully collapses this hierarchy. As concrete examples, two variations of simpler operations are considered. The first set is motivated by experimental setups, where it is natural to manipulate only two levels of the system at a time. The other set assumes fully Markovian thermal baths, which is equivalent to any process that can be described using Lindblad equations having the Gibbs state as a fixed-point. We demonstrate that catalysts, defined as auxiliary states participating in the process but returning to their original state at the end, unify thermal operations and both of the above subclasses. In particular, we adapt results from the quantum control theory to establish that catalysts thermalized to the ambient temperature are sufficient to enhance simpler operations to be as powerful as thermal operations without catalysts. Building on this result, we show that the closure of gaps in the hierarchy persists upon allowing arbitrary catalyst states for all sets of operations.

Conceptually speaking, what we demonstrate is that the notion of catalysis is a fully adequate method of encompassing all forms of non-Markovianity in thermal processes. In other words, catalysts can function as a generic and temporary memory for the operations. Furthermore, the fact that this process is catalytic implies that this non-Markovianity needs not be an additional resource which requires replenishing; instead, it can be reused indefinitely. Our work shows that non-Markovianity in the form of catalysis is the key bridging factor between experiment-friendly protocols (such as Jaynes-Cummings like thermal processes, or master equations) and the bottom-line-approach of thermal operations.

Akira Sone

University of Massachusetts Boston

Physical Advantage and Limitation of Quantum Generative Models

The main objective of the generative models is to train the generator to produce data with high accuracy and substantial diversity from a vast amount of unlabeled data, which are associated with the quality. While the quantum generative models are expected to outperform their classical counterparts, a comprehensive understanding of their physical advantage and limitation with respect to the quality has remained an open problem. We propose a quality measure called quantum inception score, which can be defined by using Holevo information. This allows us to connect the quality of the quantum generative models to the classical capacity of the quantum channels. Also, the proposed metric leads us to demonstrate that the advantage in the quality is attributed to the presence of the quantum coherences, and further that entanglement significantly enables further enhancement of the quality. Finally, we employ the fluctuation theorem approach to demonstrate that the decoherence is the primary reason for the quality degradation.

Sachin Sonkar

Indian Institute of Science Education and Research(IISER) Mohali)

Spin-based quantum Otto engines and majorization

The concept of majorization is explored as a tool to characterize the performance of a quantum Otto engine in the quasistatic regime. For a working substance in the form of a single spin of arbitrary magnitude, majorization yields a necessary and sufficient condition for the operation of the Otto engine, provided the canonical distribution of the working medium at the hot reservoir is majorized by its canonical distribution at the cold reservoir. We extend our analysis for two scenarios: a three-level atom and a bipartite system consisting of spin 1/2 interacting with an arbitrary spin via an isotropic Heisenberg exchange interaction. For both these cases, we find that while a majorization condition implies positive work extraction, it only yields sufficient conditions for the engine operation. Finally, we study the local thermodynamics of spins in the case of the bipartite system and infer an upper bound on the quantum Otto efficiency using the majorization relation.

Shou-I Tang

University of Massachusetts Boston

Quantum Thermodynamic Speed Limit in Information Processing

We generalize the second law of thermodynamics involving the information processing of an autonomous Hamiltonian system in the extended quantum version of [Phys. Rev. X 3, 041003 (2013)] in more generic scenario that the system, bath and memory are correlated initially. We first propose that the total unitary has to have its partial transpose also be a unitary operator, so that the work source plays a role as a catalyst (See Sec. III). Second, by considering the quantum speed limit of the system and memory, we define an effective quantum speed limit, which we call quantum thermodynamic speed limit (See Eq. (51)), and derived its relation to the Landauer’s bound (See Eq. (56). Focusing on quantum Stein’s lemma, we also elucidate the operational meaning of the quantum thermodynamic speed limit by associating it with quantum hypothesis testing (See Eq. (60)).

Aria Tauraso

UMBC

Thermodynamics of an Entangled Photon Gas in an Engine Cycle

The photon gas is an extensively-studied and well-understood model with a variety of applications such as describing blackbody radiation or as the working medium for a heat engine. However, it is unclear whether quantum correlations in the photon gas would notably affect the behavior of the engine, which raises the question of if one could create a heat engine that exploits genuinely quantum information by using a photon gas comprised of entangled photon pairs. If such a gas is used as the working medium, it may be possible to exploit the quantum correlations in the gas as a resource. The results obtained for thermodynamic cycles with a gas of entangled photon pairs will be presented, whilst juxtaposing them with those of the traditional photon gas.

Gabriel Tellez

Universidad de los Andes

Fast thermal equilibration: a machine learning approach

We present a way to design driving protocols that are able to achieve fast thermal equilibration of a system of interest by using techniques inspired from machine learning training algorithms. For instance, imagine a brownian particle manipulated by optical tweezers. The force on the particle can be controlled and changed over time, resulting in a driving protocol that moves the particle from an initial to a final state. Once the driving protocol ends, the system will need some additional time to relax to thermal equilibrium. It is of interest to design driving protocols that shortcut the relaxation period, so that at the end of the protocol the system is in thermal equilibrium, or very close to it. Several works [1] have tackled this problem by reverse engineering methods which consist in imposing a given evolution for the probability density function of the system and from there deduce the form of the driving protocol potential. A new method is proposed here that can be applied to more complex systems where the reverse engineering method is not viable. We simulate the evolution of a large ensemble of trajectories keeping track of the gradients with respect to a parametrization of the driving protocol. The final probability density function is compared to the target one corresponding to equilibrium. Then, using machine learning libraries, the gradients are computed via backpropagation and the protocol is adjusted accordingly until the ideal protocol is found. Similar techniques were used to design optimal protocols for the work [2]. We illustrate the effectiveness of our approach with an example: a brownian particle subjected to a harmonic potential with stiffness κ(t) following a protocol found by our method. At the end of the protocol the system reaches equilibrium with a new final value of the stiffness twice of the initial one: κf = 2κi. The equilibration was achieved in one tenth of the natural relaxation time: tf = 0.1 trelax. In general, the ratios tf /trelax and κf /κi can be arbitrarily chosen.

[1] D. Guéry-Odelin, C. Jarzynski, C. A. Plata, A. Prados, E. Trizac, Driving rapidly while remaining in control: classical shortcuts from Hamiltonian to stochastic dynamics, Rep. Prog. Phys. 86, 035902 (2023) [2] M. Engel, J. A. Smith, M. P. Brenner, Optimal control of nonequilibrium systems through automatic differentiation, https://arxiv.org/abs/2201.00098 (2022)

Ludovico Tesser

Chalmers University of Technology

Thermodynamic constraint on out-of-equilibrium noise

For mesoscopic conductors in the tunneling regime it is possible to find an exact relation between the average current and its noise [1], as long as all temperatures are equal. However, this relation fails in arbitrary out-of-equilibrium conditions.

On this poster, I will present a study of the noise going along with a tunneling current in the presence of an arbitrary temperature bias, and compare it with the noise in the absence of a temperature bias [2]. We prove that these two noises are constrained by the nonequilibrium free energy differences required to establish or deplete the temperature bias. This result emerges when one considers the thermodynamic cycle of a fictitious experiment: First, when the system is at a uniform temperature, noise is measured. Then, after work is used to establish a temperature bias, a second noise measurement is performed. Finally, the system is brought back to the initial uniform temperature, closing the cycle and producing work in the process. These measurement outcomes and the used/produced work set up a thermodynamic constraint on noise, valid for weakly coupled mesoscopic conductors with arbitrarily strong interaction and under arbitrary nonequilibrium conditions.

Devvrat Tiwari

Indian Institute of Technology Jodhpur

Role of a Canonical Hamiltonian in the Non-Markovian Quantum Thermodynamics of the Central Spin Model under Strong Coupling

We provide the exact dynamics of a central spin interacting uniformly with a spin bath and derive the canonical Hamiltonian that dictates its dynamics. We study the thermodynamic quantities, particularly entropy production, heat, work, and the change in the internal energy of this model in the strong coupling regime. The maximum work that can be extracted from the system is studied using ergotropy. Further, we explore the role of the canonical Hamiltonian in calculating the thermodynamic quantities in the strong coupling regime. This analysis provides a general picture of the strong coupling non-Markovian quantum thermodynamics.

Devjyoti Tripathy

UMBC

Quantum speed limited chaos

The quantum speed limit (QSL) characterizes the maximal rate of quantum evolution. As such, it appears obvious that the QSL can also be exploited to estimate the change in observables. In this work, we derive a QSL for Out-of-time Ordered Correlators (OTOCs), which in chaotic dynamics are described by the quantum Lyapunov exponents. For such dynamics, we express the QSL as a function of these Lyapunov exponents, which highlights the significance of the QSL also in chaotic systems. Our results are illustrated for several instances of two-dimensional Bose-Hubbard lattices.

Jake Xuereb

Atominstitut, TU Wien

The Role of Knowledge in Quantum Thermodynamics

In classical thermodynamics and statistical mechanics, the knowledge an agent possesses of a system they wish to manipulate plays a central role. If an ideal gas is in a piston and the agent is only able to access coarse-grained quantities like pressure and volume, then this agent is known to be able to extract less work from this system than a demon possessing knowledge of the momenta of each particle in this gas. In quantum thermodynamics we are lacking an analogous understanding of the role of knowledge. In particular;

i) What resources (control, memory, correlations…) must an agent spend to acquire knowledge of a quantum state? ii) How does the knowledge of the agent limit their ability to transform the state of the system?

In this work we answer these questions by developing a thermodynamic framework that connects knowledge acquisition and state transformation. Our approach ties together and makes use of resource theory [1], von Neumann measurements with thermal probes [2] and optimal cloning machines [3,4].

We consider a setting where an agent is studying a quantum system in a fixed state which is unknown to them. The goal of the agent, who has access to a finite number of copies of this unknown state, is to interact with some of these copies to obtain an estimate of the unknown state and using the knowledge gained transform the remaining copies to achieve a goal (e.g. work extraction). The agent is able to estimate this state in a sequential scenario where they correlate the unknown copies with ancillae one at a time, allowing them to obtain knowledge of the system by sampling the ancillae which act as a memory. We investigate the resources (no. of copies, rank of ancilla, thermality of ancilla, correlations) required for the agent to estimate the state of the system up to a given fidelity. Comparing this with a single-shot scenario using an optimal cloning machine which gives the best possible state estimate under the rules of quantum mechanics, we lower bound the cost of obtaining optimal knowledge of the state of the system.

We then illustrate these results by examining how the space of states the agent can transform the system into under the free operations of a resource theory (namely thermal operations and LOCC operations) changes depending on the thermodynamic resources invested to acquire this knowledge. The more knowledge, the lower the entropy of the estimated state and the more states the agent can transform the system to.

With this work we aim to connect state estimation to quantum thermodynamics in a novel way which can inform firstly how we think of agents in quantum theory and secondly what resources lie behind operations that are deemed to be free. As they are only free to agents possessing the knowledge to see these operations as free.

Whilst this work is not yet on the arXiv, we aim to upload it during QTD2024.

[1] - Quantum resource theories, E. Chitambar and G. Gour, Rev. Mod. Phys. 91, 025001 (2019) [2] - Ideal Projective Measurements Have Infinite Resource Cost, Y. Guryanova, N. Friis, M. Huber, Quantum 4, 222 (2020) [3] - Quantum Cloning, V. Scarani, S. Iblisdir, N. Gisin, A. Acin, Rev. Mod. Phys. 77, 1225 (2005) [4] - Asymptotic Quantum Cloning is State Estimation, J. Bae, A. Acin, Phys. Rev. Lett. 97, 030402 (2006)

Yuxin Wang

University of Maryland, College Park

Evidence for breaking of quantum detailed balance in non-Gaussian fluctuations of a driven-dissipative cavity

Understanding how to accurately describe fluctuations in driven-dissipative quantum systems is a question of fundamental interest with implications in formulating fluctuations relations. Such knowledge is also useful for designing control protocols that enable high-fidelity quantum operations. Here, we employ the Keldysh approach to quantum noise characterization to quantify frequency-dependent non-Gaussian fluctuations of a quantum system. Making use of a general mapping between a moment-generating function of quantum fluctuations and a Keldysh path integral, our approach allows an exact evaluation of the higher-order fluctuations. We demonstrate the utility of our approach through the paradigmatic example of photon shot noise fluctuations in a driven bosonic mode, where we analytically derive the leading-order non-Gaussian corrections to those frequency-dependent fluctuations, also known as the quantum bispectrum. Our results reveal distinctive nonclassical noise properties of the system, including an effective breaking of detailed balance by quantum fluctuations. The quantum bispectrum can be experimentally measured using existing noise spectroscopy protocols.

Maggie Williams

UMBC

The Stochastic Thermodynamics of Aging

High school biology traditionally attributes aging to DNA mutation, resulting in cellular dysfunction during self-replication. A novel perspective now arises, emphasizing the statistical interpretation of cell mutation. Healthy cells exhibit low entropy and high energy production, indicative of order. Conversely, mutating cells experience reduced efficiency, lower energy production, and increased entropy. Upon cell death, entropy reaches its maximum. The probabilistic nature of DNA prompts a shift toward understanding aging through statistical thermodynamics, enabling the formulation of a mathematical model. This research delves into the thermodynamics of biological processes, framing macroscopic aging as entropy’s function. The focus is on a three-state mechanical model akin to Maxwell’s demon, which reaches a periodic steady state with an incoming bitstream over time. The research introduces a time-dependent modification to the rotation rate of the demon, gradually decreasing until the demon’s ability to transcribe information becomes too inefficient, mimicking system ‘death’ analogous to cell demise. Solving the master equation analytically reveals a monotonically increasing entropy over time. This study bears significant implications, suggesting living systems operate statistically, allowing for the construction of probabilistic models to quantify their behavior.

Marek Winczewski

University of Gdańsk

Filtered Approximation to The Refined Weak Coupling Limit

The famous Davies-GKSL secular Markovian master equation is tremendously successful in approximating the evolution of open quantum systems in terms of just a few parameters. However, the fully-secular Davies-GKSL equation fails to accurately describe time scales short enough, i.e., comparable to the inverse of differences of frequencies present in the system of interest. A complementary approach that works well for short times but is not suitable after this short interval is known as the quasi-secular master equation. Still, both approaches fail to have any faithful dynamics in the intermediate time interval. Simultaneously, descriptions of dynamics that apply to the aforementioned ``grey zone’’ often are computationally much more complex than master equations or are mathematically not well-structured. The filtered approximation (FA) to the refined weak coupling limit has the simplistic spirit of the Davies-GKSL equation and allows capturing the dynamics in the intermediate time regime. At the same time, our non-Markovian equation yields completely positive dynamics. We exemplify the performance of the FA equation in the cases of the spin-boson system and qutrit-boson system in which two distant time scales appear, by comparing it with the numerically exact method of HEOM. Additionally, we benchmark the FA equation on the testbed of a damped quantum harmonic oscillator where we compare it to the exact solution of Heisenberg-Langevin equations.

Yuxin Wu

Peking University

Scaling relations for finite-time first-order phase transition

The theory of equilibrium phase transition, which traditionally does not involve time evolution, concerns only static quantities. In recent decades, owing to the development of nonequilibrium thermodynamics, there is a growing interest in nonequilibrium phase transition which concerns time evolution. It is well-known that in the absence of phase transitions, the excess work resulted from finite-rate quench is proportional to the quench rate $v$. The time evolution in a second-order phase transition can be understood via the Kibble-Zurek mechanism, and the scaling of work is related to the critical exponents. Nevertheless, the finite-time nonequilibrium thermodynamics of the first-order phase transition remains largely unexplored. We investigate the scaling relations of some thermodynamic quantities with the quench rate in the first-order phase transition. It is shown that the excess work scales as $v^{2/3}$ for small quench rate. Moreover, the delay time and the transition time scale as $v^{-1/3}$. Our study deepens the understanding about the nonequilibrium thermodynamics of the first-order phase transition.

André Hernandes Alves Malavazi

International Centre for Theory of Quantum Technologies (ICTQT) - University of Gdańsk

Unveiling Detuning Effects for Heat-Current Control in Quantum Thermal Devices

Navigating the intricacies of thermal management at the quantum scale is a challenge in the pursuit of advanced nanoscale technologies. To this extent, theoretical frameworks introducing minimal models mirroring the functionality of electronic current amplifiers and transistors, for instance, have been proposed. Different architectures of the subsystems composing a quantum thermal device can be considered, tacitly bringing drawbacks or advantages if properly engineered.This paper extends the prior research on thermotronics, studying a strongly coupled three-subsystem thermal device with a specific emphasis on a third excited level in the control subsystem. Our setup can be employed as a multipurpose device conditioned on the specific choice of internal parameters: heat switch, rectifier, stabilizer, and amplifier. The exploration of the detuned levels unveils a key role in the performance and working regime of the device. We observe a stable and strong amplification effect persisting over broad ranges of temperature. We conclude that considering a three-level system, as the one directly in contact with the control temperature, boosts output currents and the ability to operate our devices as a switch at various temperatures.

Zakaria Mzaouali

Institute of Theoretical and Applied Informatics, Polish Academy of Sciences

Efficiency Optimization in Quantum Computing: Balancing Thermodynamics and Computational Performance

We investigate the computational efficiency and thermodynamic cost of the D-Wave quantum annealer under reverse-annealing with and without pausing. Our experimental results demonstrate that the combination of reverse-annealing and pausing leads to improved computational efficiency while minimizing the thermodynamic cost compared to reverse-annealing alone. Moreover, we find that the magnetic field has a positive impact on the performance of the quantum annealer during reverse-annealing but becomes detrimental when pausing is involved. Our results provide strategies for optimizing the performance and energy consumption of quantum annealing systems employing reverse-annealing protocols.

Alexandria Udenkwo

Washington University in St. Louis

Characterizing the energy and efficiency of an entanglement fueled engine in a circuit QED processor

As the NISQ era of quantum technologies requires robust error correcting protocols, the role and limits of local measurement and feedback become incredibly important. To help elucidate the fundamental limits of quantum measurement and feedback, we investigate the thermodynamic consequences of such operations in the context of fueling an engine. Critical to the engine’s operation is the measurement observable not commuting with the system Hamiltonian, wherein a net change in the energy of the system is predicted to occur. In some cases, local measurement does not commute with the global Hamiltonian, leading to collapse of entanglement in a system. For our case, this collapse breaks the binding energy within the system, which gives an energy change that serves as the engine’s fuel. Hence, a cycle can be implemented to facilitate energy exchanges between the system and measurement apparatus. Understanding these energy flows is of importance for the implementation of error correction in quantum devices. We realize the engine using circuit-QED architecture, with a chain of three transmon qubits. We study the energy and entropy transfers between system and measurement apparatus as well as the efficiency of the engine, determined by the ratio of energy extracted and the entropy produced.

Sangyun Lee

University of Maryland & Korea Institute For Advanced Study

Detecting area laws for entanglement entropy via machine learning

Entropy is an important quantity in various research fields from information theory to quantum thermodynamics. Because of its importance, there are various efforts to estimate the entropy. However, it turned out that entropy is one of the thermodynamic quantities under the curse of dimensionality. In the case of quantum entropies, quantumness adds another layer of difficulty. In this talk, I present a novel method to estimate quantum entropies. We employ a deep neural network that has shown high performance with high dimensional data and combine the neural network with quantum circuits. Our method shows high accuracy with enough data. Because this method is based on a quantum entropy bound, our method can be used as a quantum-phase classifier even with a small data set. We verified our algorithm on a XXZ chain model. This research is accepted in physical review E.

Marcin Łobejko

University of Gdansk

Work and Fluctuations: Coherent vs. Incoherent Ergotropy Extraction

Extension of fluctuation theorems to a quantum domain presents a challenge that has been discussed by numerous authors, which typically requires the introduction of quasi-probabilities. In the study [1], I consider a similar path introducing a novel quasi-probability concept based on convolution operation; however, to recognize the purely quantum contributions, the framework is applied to work extraction via an explicit quantum battery defined by the ideal weight. Within this fully quantum setup, I study the difference between fluctuations in extraction of the coherent and incoherent part of the system’s ergotropy. It is revealed that while coherent extraction can diminish fluctuations in the weight, its absolute value must diverge as more work is extracted. Conversely, the opposite holds true for the extraction of incoherent ergotropy. These findings reveal the connections between three approaches to quantum fluctuations: work operator (W), two-point measurement (TPM), and the newly introduced quasi-probability (QP). Notably, based on these results, I was able to identify a purely quantum contribution that emerges for non-classical states of the battery, directly responsible for reducing work fluctuations (impossible to capture within the frameworks with implicit battery).

[1] Marcin Lobejko. Work and Fluctuations: Coherent vs. Incoherent Ergotropy Extraction. Quantum, 6:762, July 2022. ISSN 2521-327X. doi:10.22331/q-2022-07-14-762. URL https://doi.org/10.22331/q-2022-07-14-762

Sanghita Sengupta

Howard University

Exploring growth dynamics and critical phenomena in the agential decision-making behaviors of Physarum polycephalum

We investigate the growth dynamics and agential decision-making behaviors of Physarum polycephalum, a single-celled, multinucleate slime mold known for its remarkable problem-solving capabilities, despite lacking neuronal connections. Employing graph-theoretic methods with a special focus on edges connecting nodes (vertices), we analyze variations in network features across diverse biological strains and quantify parameters relative to the organism’s age (from sclerotia revival) and nutrient availability. Our exploration of the hierarchical network of tubular veins within Physarum polycephalum aims to unveil the mechanisms underpinning its information-processing capabilities. Additionally, we investigate mass sensing, morphological changes related to the area and perimeter of the organismic growth, and energy flow within the network to elucidate thermodynamic optimization principles, facilitating the analysis of how network structures at different scales of self-organization evolve in the course of hours for efficient energy and information transfer. Furthermore, our inquiry investigates critical phenomena in these network dynamics, with a focus on phase transitions and emergent critical behavior. This research enriches our understanding of the physical principles governing the emergence of complexity in aneural biological systems operating far from thermal equilibrium.

Cameron Witkowski

University of Toronto

On the Precise Link Between Energy and Information

We present a modified version of the Szilard engine, demonstrating that an explicit measurement procedure is entirely unnecessary for its operation. By considering our modified engine, we are able to provide a new interpretation of Landauer’s original argument for the cost of erasure. From this view, we demonstrate that a reset operation is strictly impossible in a dynamical system with only conservative forces. Then, we prove that approaching a reset yields an unavoidable instability at the reset point. Finally, we present an original proof of Landauer’s principle that is completely independent from the Second Law of thermodynamics.