arXiv subjects

Shanhe Su

Publications and source records attributed to Shanhe Su.

36 records · Page 2Linked to original sources

arXiv2024

Efficiency bounds for bipartite information-driven thermodynamic systems

This study introduces a novel approach to derive a lower bound for the entropy production rate of a subsystem by utilizing the Cauchy-Schwarz inequality. It extends to establishing comprehensive upper and lower bounds for the efficiency of two subsystems. These bounds are applicable to a wide range of Markovian stochastic processes, which enhances the accuracy in depicting the range of energy conversion efficiency between subsystems. Empirical validation is conducted using a two-quantum-dot system model, which serves to confirm the effectiveness of our inequality in refining the boundaries of efficiency.

cond-mat.stat-mech↗

arXiv2024

Breakthrough of a cross-century problematic issue:The perfect statements of the third law of thermodynamics

The third law of thermodynamics has been verified experimentally, but how to perfectly express such a law in theory has become a cross-century problematic issue. It is found from the recent researches that by introducing an innovative method, the Nernst equation can be obtained directly from the experimental data of chemical reactions at low temperatures without the need for artificial additional assumptions appearing in textbooks, so that the Nernst theorem should be replaced by the Nernst statement. The heat capacity statement proposed recently can be also obtained from the experimental data of the heat capacity at low temperatures. The heat capacity statement and the Nernst statement are proved to be mutually derivable and the two are equivalent. The unattainability statement of absolute zero temperature is only a coloration of the Nernst statement or the heat capacity statement. Simultaneously, the defects and deficiencies related to the contents of the third law of thermodynamics appearing in textbooks are pointed out and corrected. The results obtained show clearly that the Nernst theorem and the unattainability statement of absolute zero temperature should be withdrawn from the statements of the third law of thermodynamics. It is important to find that the Nernst statement and the heat capacity statement are two equivalent statements of the third law of thermodynamics, which can solve the centennial debate problems of the third law of thermodynamics and supply the perfect statements for the third law of thermodynamics.

cond-mat.stat-mech↗

arXiv2023

Theoretical bound of the efficiency of learning with coarse-graining

A thermodynamic formalism describing the efficiency of information learning is proposed, which is applicable for stochastic thermodynamic systems with multiple internal degree of freedom. The learning rate, entropy production rate (EPR), and entropy flow from the system to the environment under coarse-grained dynamics are derived. The Cauchy-Schwarz inequality has been applied to demonstrate the lower bound on the EPR of an internal state. The inequality of EPR is tighter than the Clausius inequality, leading to the derivative of the upper bound on the efficiency of learning. The results are verified in cellular networks with information processes.

cond-mat.stat-mech↗

arXiv2023

Performance improvement of a fractional quantum Stirling heat engine

To investigate the impact of fractional parameter on the thermodynamic behaviors of quantum systems, we incorporate fractional quantum mechanics into the cycle of a quantum Stirling heat engine and examine the influence of fractional parameter on the regeneration and efficiency. We propose a novel approach to control the thermodynamic cycle that leverages the fractional parameter structure and evaluates its effectiveness. Our findings reveal that by tuning the fractional parameter, the region of the cycle with the perfect regeneration and the Carnot efficiency can be expanded.

quant-ph↗

arXiv2022

On the equivalence of the Nernst theorem and its consequence

One general consequence of the Nernst theorem is derived, i.e., the various heat capacities of a thermodynamic system under different constraints approach zero as the temperature approaches absolute zero. The temperature dependence of the heat capacity of any thermodynamic system at ultra-low temperatures is revealed through this consequence. Moreover, the general form and the simplest expression of the heat capacities of thermodynamic systems at ultra-low temperatures are deduced. Some significant discussion and results are given. One new research method is provided by using this consequence. Finally, the equivalence between the Nernst theorem and its consequence is rigorously proved, so that this consequence may be referred to another description of the third law of thermodynamics.

cond-mat.stat-mech↗

arXiv2022

The roles of quantum coherence in thermodynamic processes

Quantum coherence associated with the superpositions of two different sets of eigenbasis vectors has been regarded as essential in thermodynamics. It is found that coherent factors can be determined by writing observables as an expansion in the basis vectors of the systemic density operator and Hamiltonian. We reveal the roles of coherence in finite-time thermodynamic processes, such as the spin precession and the spontaneous emission of a photon. Results show that the work in the spin precession and the heat in the spontaneous emission process are mainly generated by coherence.

quant-ph↗

arXiv2022

Finite-time quantum measurement cooling beyond the Carnot limit

We proposed the finite-time cycle model of a measurement-based quantum cooler, where invasive measurement provides the power to drive the cooling cycle. Such a cooler may be regarded as an alternative thought experiment of Mawell's demon. The measurement-feedback information is capable of moving heat from the cold to hot bath without any work input and even making the maximum coefficient of performance larger than the Carnot limit. The causes that this seemingly paradoxical result does not violate the laws of thermodynamics can be clearly explained through the derivation of a generalized Clausius inequality including the mutual information.

quant-ph↗

arXiv2021

The optimum configuration design of a nanostructured thermoelectric device with resonance tunneling

A nanostructured thermoelectric device is designed by connecting a double-barrier resonant tunneling heterostructure to two electron reservoirs. Based on Landauers equation and Fermi-Dirac statistics, the exact solution of the heat flow is calculated. The maximum power output and efficiency are calculated through the optimizations of several key parameters. The optimum characteristic curve of the performance is obtained. The reasonably working region of the device is determined, the selection criteria of main parameters are provided, and the optimum configuration of the device is drawn. Results show that the heterojunction becomes a perfect energy filter by appropriately regulating the chemical potentials of electron reservoirs and optimally choosing the widths of barrier and quantum well and the nanostructured thermoelectric device with resonance tunneling may obtain simultaneously a large power output and a high efficiency.

cond-mat.mes-hall↗

arXiv2021

Thermal divergences of quantum measurement engine

A quantum engine fueled by quantum measurement is proposed. Under the finite-time adiabatic driving regime, the conversion of heat to work is realized without the compression and expansion of the resonance frequency. The work output, quantum heat, and efficiency are derived, highlighting the important role of the thermal divergence recently reappearing in open quantum systems. The key problem of how the measurement basis can be optimized to enhance the performance is solved by connecting the thermal divergence to the nonequilibrium free energy and entropy. The spin-engine architecture offers a comprehensive platform for future investigations of extracting work from quantum measurement.

quant-ph↗

arXiv2021

The reverse flow and amplification of heat in a quantum-dot system

We demonstrate that when a quantum dot is embedded between the two reservoirs described by different statistical distribution functions, the reverse flow and amplification of heat can be realized by regulating the energy levels of the quantum dot and the chemical potentials of two reservoirs. The reverse heat flow and amplification coefficient of the quantum device are calculated. The novelty of this device is that the reverse flow of heat does not need externally driving force and this seemingly paradoxical phenomenon does not violate the laws of thermodynamics. It is further expounded that the quantum device has some practical applications. For example, the device can work as a micro/nano cooler. Moreover, the performance characteristics of the cooler are revealed for different distribution functions. The coefficients of performance of the cooler operated at different conditions are calculated and the optimum selection criteria of key parameters are supplied.

cond-mat.mes-hall↗

arXiv2021

Suppressing coherence effects in quantum-measurement based engines

The recent advances in the study of thermodynamics of microscopic processes have driven the search for new developments in energy converters utilizing quantum effects. We here propose a universal framework to describe the thermodynamics of a quantum engine fueled by quantum projective measurements. Standard quantum thermal machines operating in a finite-time regime with a driven Hamiltonian that does not commute in different times have the performance decreased by the presence of coherence, which is associated with a larger entropy production and irreversibility degree. However, we show that replacing the standard hot thermal reservoir by a projective measurement operation with general basis in the Bloch sphere and controlling the basis angles suitably could improve the performance of the quantum engine as well as decrease the entropy change during the measurement process. Our results go in direction of a generalization of quantum thermal machine models where the fuel comes from general sources beyond the standard thermal reservoir.

quant-ph↗

arXiv2020

Stochastic Floquet quantum heat engines and stochastic efficiencies

Based on the notion of quantum trajectory, we present a stochastic theoretical framework for Floquet quantum heat engines. As an application, the large deviation functions of two types of stochastic efficiencies for a two-level Floquet quantum heat engine are investigated. We find that the statistics of one efficiency agree well with the predictions of the universal theory of efficiency fluctuations developed by Verley et al. [Phys. Rev. E {\bf 90}, 052145 (2014)], whereas the statistics of the other efficiency do not. The reason for this discrepancy is attributed to the lack of fluctuation theorems for the latter type of efficiency.

cond-mat.stat-mech↗

arXiv2020

Thermal rectification and negative differential thermal conductivity based on a parallel-coupled double quantum-dot

We investigate the heat flow transport properties of a parallel-coupled double quantum-dot system connected to two reservoirs with a temperature bias in the Coulomb blockade regime. We demonstrate that the effects of thermal rectification and negative differential thermal conductance (NDTC) exist in this system and analyze the influences of energy level difference and Coulomb interaction on the thermal rectification and NDTC. We find that this system can achieve a high thermal rectification ratio and NDTC when the asymmetry factor of the system is enhanced.

cond-mat.mes-hall↗

arXiv2020

Nonequilibrium free energy and information flow of a double quantum-dot system with Coulomb coupling

We build a double quantum-dot system with Coulomb coupling and aim at studying the connections among the entropy production, free energy, and information flow. By utilizing the concepts in stochastic thermodynamics and graph theory analysis, the Clausius and nonequilibrium free energy inequalities are built to interpret the local second law of thermodynamics for subsystems. A fundamental set of cycle fluxes and affinities is identified to decompose the two inequalities by using Schnakenberg's network theory. The results show that the thermodynamic irreversibility has the energy-related and information-related contributions. A global cycle associated with the feedback-induced information flow would pump electrons against the bias voltage, which implements a Maxwell Demon.

cond-mat.stat-mech↗

arXiv2020

Coherence induced work in quantum heat engines with Larmor precession

The impacts of quantum coherence on nonequilibrium thermodynamics become observable by dividing the heat and work into the conventional diagonal part and the other part relaying on the superpositions and the time derivative of Hamiltonian. Specializing to exactly-solvable dynamics of Larmor precession, we build a quantum Otto heat engine employing magnetic-driven atomic rotations. The coherence induced by the population transition guarantees the positive work output when the control protocol is time dependent. The time-dependent control of a quantum heat engine implements the correspondence between the classical and quantum adiabatic theorems for microscopic heat machines.

quant-ph↗

arXiv2019

Thermodynamic coupling rule for far-from-equilibrium systems

The energy conversion efficiency of far-from-equilibrium systems is generally limited by irreversible thermodynamic fluxes that make contact with different heat baths. For complex systems, the states of the maximum efficiency and the minimum entropy production are usually not equivalent. Here we show that the proper adjustments of the interaction between the energy and matter currents offer some important criteria for the performance characterizations of thermal agents, regardless of the system types and transition protocols. The universal thermodynamic coupling rule plays a critical role in irreversible processes. A double quantum dot system is applied to demonstrate that the performances of heat engines or refrigrators can be enhanced by suitably adjusting the coupling strength between thermodynamic fluxes.

quant-ph↗

arXiv2018

Quantum coherence thermal transistors

Coherent control of self-contained quantum systems offers the possibility to fabricate smallest thermal transistors. The steady coherence created by the delocalization of electronic excited states arouses nonlinear heat transports in non-equilibrium environment. Applying this result to a three-level quantum system, we show that quantum coherence gives rise to negative differential thermal resistances, making the thermal transistor suitable for thermal amplification. The results show that quantum coherence facilitates efficient thermal signal processing and can open a new field in the application of quantum thermal management devices.

quant-ph↗

arXiv2014

Hybrid photovoltaic and electron-tunneling converters

Photon impingement is capable of liberating electrons in semiconductors. When the electron transport is primarily governed by temperature gradients, high irreversibilities will result, thus lowering converters' efficiencies. A fundamental study in the absence of photovoltaics\cite{1} has achieved the reduction of these irreversibilities by considering entropy changes due to electron flows. Here we present an unreported mechanism that integrates photovoltaic conversion and electron tunneling. Photon-excited electrons that occupy energy levels beyond windowed limits are first imprisoned inside the cathode, then given opportunities to rapidly re-thermalize, and eventually allowed to enter the tunnel. Energies wasted by both the irreversibility and the recombination are minimized with respect to the transmission energy and the transmission window that characterize the tunnel. Upon application of this mechanism to high-concentration solar cells, the proposed hybrid model outperforms others. It further provides a guide for elevating efficiencies in future photon-to-electron converters typified by third-generation photovoltaic systems.

cond-mat.mtrl-sci↗