Quantum Heat Research Articles

Non-Markovian effects on the performance of a quantum Otto refrigerator

Quantum thermodynamics is an important infrastructure for developing and performing many tasks in quantum technologies. In this paper, we propose a model for constructing an Otto refrigerator thermal machine via an auxiliary system and Markovian reservoir. Moreover, the proposed model induces Markovian and/or non-Markovian regimes on refrigerant systems. By increasing the coupling strength between the refrigerant and auxiliary systems, non-Markovian behaviors arise in different thermodynamic quantities. In addition, the different amounts of quantum thermodynamics, namely work, heat and coefficient of performance, are investigated as a function of the initial frequency of the refrigerant system. Our results show that the memory effects between the open system and the environment can enhance the power of the proposed Otto refrigerator, particularly in the finite-time strokes of the refrigerator, under some specific circumstances.

Single-atom quantum heat engine based on electromagnetically induced transparency

Single-atom quantum heat engine based on electromagnetically induced transparency

Spectral asymptotics of elliptic operators on manifolds

The study of spectral properties of natural geometric elliptic partial differential operators acting on smooth sections of vector bundles over Riemannian manifolds is a central theme in global analysis, differential geometry and mathematical physics. Instead of studying the spectrum of a differential operator [Formula: see text] directly one usually studies its spectral functions, that is, spectral traces of some functions of the operator, such as the spectral zeta function [Formula: see text] and the heat trace [Formula: see text]. The kernel [Formula: see text] of the heat semigroup [Formula: see text], called the heat kernel, plays a major role in quantum field theory and quantum gravity, index theorems, non-commutative geometry, integrable systems and financial mathematics. We review some recent progress in the study of spectral asymptotics. We study more general spectral functions, such as [Formula: see text], that we call quantum heat traces. Also, we define new invariants of differential operators that depend not only on the eigenvalues but also on the eigenfunctions, and, therefore, contain much more information about the geometry of the manifold. Furthermore, we study some new invariants, such as [Formula: see text], that contain relative spectral information of two differential operators. Finally, we show how the convolution of the semigroups of two different operators can be computed by using purely algebraic methods.

Optimal performance of voltage-probe quantum heat engines

Optimal performance of voltage-probe quantum heat engines

Thermodynamics and fluctuations in finite-time quantum heat engines under reservoir squeezing

Thermodynamics and fluctuations in finite-time quantum heat engines under reservoir squeezing

Guiding the Driving Factors on Plasma Super-Photothermal S-Scheme Core-Shell Nanoreactor to Enhance Photothermal Catalytic H2 Evolution and Selective CO2 Reduction.

Light-induced heat has a non-negligible role in photocatalytic reactions. However, it is still challenging to design highly efficient catalysts that can make use of light and thermal energy synergistically. Herein, the study proposes a plasma super-photothermal S-scheme heterojunction core-shell nanoreactor based on manipulation of the driving factors, which consists of α-Fe2 O3 encapsulated by g-C3 N4 modified with gold quantum dots. α-Fe2 O3 can promote carrier spatial separation while also acting as a thermal core to radiate heat to the shell, while Au quantum dots transfer energetic electrons and heat to g-C3 N4 via surface plasmon resonance. Consequently, the catalytic activity of Au/α-Fe2 O3 @g-C3 N4 is significantly improved by internal and external double hot spots, and it shows an H2 evolution rate of 5762.35µmol h-1 g-1 , and the selectivity of CO2 conversion to CH4 is 91.2%. This work provides an effective strategy to design new plasma photothermal catalysts for the solar-to-fuel transition.

Quantum Heat Engine with Level Degeneracy for Oscillator-shaped Potential Well

Quantum Heat Engine with Level Degeneracy for Oscillator-shaped Potential Well

Simulation of optimal work extraction for quantum systems with work storage

The capacity to extract work from a quantum heat machine is not only of practical value but also lies at the heart of understanding quantum thermodynamics. In this paper, we investigate optimal work extraction for quantum systems with work storage, where extracting work is completed by a unitary evolution on the composite system. We consider the physical requirement of energy conservation both strictly and on average. For both, we construct their corresponding unitaries and propose variational quantum algorithms for optimal work extraction. We show that maximal work extraction in general can be feasible when energy conservation is satisfied on average. We demonstrate with numeral simulations using a continuous-variable work storage. Our work show an implementation of a variational quantum computing approach for simulating work extraction in quantum systems.

Wigner Equations for Phonons Transport and Quantum Heat Flux

Starting from the quantum Liouville equation for the density operator and applying the Weyl quantization, Wigner equations for the acoustic, optical and Z phonons are deduced. The equations are valid for any solid, including 2D crystals like graphene. With the use of Moyal’s calculus and its properties, the pseudo-differential operators are expanded up to the second order in ħ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbar $$\\end{document}. An energy transport model is obtained by using the moment method with closure relations based on a quantum version of the Maximum Entropy Principle by employing a relaxation time approximation for the production terms of energy and energy flux. An explicit form of the thermal conductivity with quantum correction up to ħ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbar ^2$$\\end{document} order is obtained under a long-time scaling for the most relevant phonon branches.

Highly efficient quantum heat engine operating at maximum power in the α-T3 lattice

The α−T3 lattice, an interpolation of graphene's honeycomb lattice and the dice lattice, has drawn a lot of attention. Herein, the thermoelectric properties of the α−T3 lattice based junction are investigated. The parameter φ and the gate voltage Vg can be utilized for adjusting thermoelectric properties. Without the mass term Δ, the efficiency at maximum power η is relatively low, similar to two-dimensional graphene. When Δ is introduced, the initially flat band warps and disperses, resulting in a band gap between the distorted flat band and the conduction (valence) band. In this case, the maximum power and η are both greatly enhanced and are adjustable by Vg and φ. With high output power, η can be higher than 0.3 Carnot efficiency. As a result, it is suggested that the α−T3 lattice will be utilized to create a highly efficient quantum heat engine.

Wave-particle duality in a quantum heat engine

Wave-particle duality in a quantum heat engine

Quantum heat valve and entanglement in superconducting LC resonators

Quantum superconducting circuit with flexible coupler has been a powerful platform for designing quantum thermal machines. In this Letter, we employ the tunable coupling of two superconducting resonators to realize a heat valve by modulating magnetic flux using a superconducting quantum interference device. It is shown that a heat valve can be realized in a wide parameter range. We find a consistent relation between the heat current and quantum entanglement, which indicates the dominant role of entanglement on the heat valve. It provides an insightful understanding of quantum features in quantum heat machines.

Learning coherences from nonequilibrium fluctuations in a quantum heat engine

Learning coherences from nonequilibrium fluctuations in a quantum heat engine

Quantum dissipation and the virial theorem

In this note, we study the celebrated virial theorem for dissipative systems, both classical and quantum. The classical formulation is discussed and an intriguing effect of the random force (noise) is made explicit in the context of the virial theorem. Subsequently, we derive a generalized virial theorem for a dissipative quantum oscillator, i.e. a quantum oscillator coupled with a quantum heat bath. Such a heat bath is modelled as an infinite collection of independent harmonic oscillators with a certain distribution of initial conditions. In this situation, the non-Markovian nature of the quantum noise leads to novel bath-induced terms in the virial theorem. We also consider the case of an electrical circuit with thermal noise and analyze the role of non-Markovian quantum noise in the context of the virial theorem.

Universal Scaling Bounds on a Quantum Heat Current.

In this Letter, we derive new bounds on a heat current flowing into a quantum L-particle system coupled with a Markovian environment. By assuming that a system Hamiltonian and a system-environment interaction Hamiltonian are extensive in L, we prove that the absolute value of the heat current scales at most as Θ(L^{3}) in a limit of large L. Furthermore, we present an example of noninteracting particles globally coupled with a thermal bath, for which this bound is saturated in terms of scaling. However, the construction of such a system requires many-body interactions induced by the environment, which may be difficult to realize with the existing technology. To consider more feasible cases, we consider a class of the system where any nondiagonal elements of the noise operator (derived from the system-environment interaction Hamiltonian) become zero in the system energy basis, if the energy difference exceeds a certain value ΔE. Then, for ΔE=Θ(L^{0}), we derive another scaling bound Θ(L^{2}) on the absolute value of the heat current, and the so-called superradiance belongs to a class for which this bound is saturated. Our results are useful for evaluating the best achievable performance of quantum-enhanced thermodynamic devices, including far-reaching applications such as quantum heat engines, quantum refrigerators, and quantum batteries.

Quantum heat machines enabled by twisted geometry

In this paper, we analyze the operation of an Otto cycle heat machine driven by a non-interacting two-dimensional electron gas on a twisted geometry. We show that due to both the energy quantization on this structure and the adiabatic transformation of the number of complete twists per unit length of a helicoid, the machine performance in terms of output work, efficiency, and operation mode can be altered. We consider the deformations as in a spring, which is either compressed or stretched from its resting position. The realization of classically inconceivable Otto machines, with an incompressible sample, can be realized as well. The energy-level spacing of the system is the quantity that is being either compressed or stretched. These features are due to the existence of an effective geometry-induced quantum potential which is of pure quantum-mechanical origin.

Relativistic quantum heat engine with the presence of minimal length

The presence of a minimal length has a significant effect on relativistic physical systems. This paper discusses how minimal length affects the efficiency of a relativistic quantum heat engine. The working substance chosen is a Dirac particle trapped in a one-dimensional infinite potential well. In this paper, we calculate the efficiency of a quantum heat engine in three thermodynamic cycles, namely the Carnot, Otto, and Brayton cycles. The engine efficiency is calculated analytically and numerically. In this research, the minimal length is a correction factor for the relativistic energy. The result is that the minimal length could increase or decrease the efficiency of the relativistic quantum heat engine on the small potential width according to the particle mass, the expansion parameter, and the thermodynamic cycle.

Efficiency and thermodynamic uncertainty relations of a dynamical quantum heat engine

In the quest for high-performance quantum thermal machines, looking for an optimal thermodynamic efficiency is only part of the issue. Indeed, at the level of quantum devices, fluctuations become extremely relevant and need to be taken into account. In this paper we study the thermodynamic uncertainty relations for a quantum thermal machine with a quantum harmonic oscillator as a working medium, connected to two thermal baths, one of which is dynamically coupled. We show that parameters can be found such that the machine operates both as a quantum engine or refrigerator, with both sizeable efficiency and small fluctuations.

Model-free optimization of power/efficiency tradeoffs in quantum thermal machines using reinforcement learning.

A quantum thermal machine is an open quantum system that enables the conversion between heat and work at the micro or nano-scale. Optimally controlling such out-of-equilibrium systems is a crucial yet challenging task with applications to quantum technologies and devices. We introduce a general model-free framework based on reinforcement learning to identify out-of-equilibrium thermodynamic cycles that are Pareto optimal tradeoffs between power and efficiency for quantum heat engines and refrigerators. The method does not require any knowledge of the quantum thermal machine, nor of the system model, nor of the quantum state. Instead, it only observes the heat fluxes, so it is both applicable to simulations and experimental devices. We test our method on a model of an experimentally realistic refrigerator based on a superconducting qubit, and on a heat engine based on a quantum harmonic oscillator. In both cases, we identify the Pareto-front representing optimal power-efficiency tradeoffs, and the corresponding cycles. Such solutions outperform previous proposals made in the literature, such as optimized Otto cycles, reducing quantum friction.

Thermodynamics of one and two-qubit nonequilibrium heat engines running between squeezed thermal reservoirs

Quantum heat engines form an active field of research due to their potential applications. There are several phenomena that are unique to the quantum regime, some of which are known to give these engines an edge over their classical counterparts. In this work, we focus on the study of one and two-qubit finite-time Otto engines interacting with squeezed thermal baths, and discuss their important distinctions as well as the advantage of using the two-qubit engine. In particular, the two-qubit engine offers an interesting study of the interplay between the degree of squeezing and that of the coherence between the two qubits. We find that the two-qubit engine generally yields higher power than its one-qubit counterpart. The effective temperature of the squeezed baths can be calculated both for the one and two-qubit engines, and they tend to show an exponential growth with increase in squeezing parameters $r_h$ and $r_c$. It is also observed that by tuning the squeezing parameters, the machine can be made to work either in the engine or in the refrigerator mode. Additional effects due to the change in the inter-qubit separation have been studied.