arXiv subjects

Ousi Pan

Publications and source records attributed to Ousi Pan.

9 recordsLinked to original sources

arXiv2026

Balancing Power, Efficiency, and Constancy under Broken Time-Reversal Symmetry

We derive general trade-off relations among the power, efficiency, and constancy for two-terminal thermoelectric systems in the linear response regime. Constancy, which quantifies the steadiness of the heat engine, is measured by its fluctuations. The bounds of the efficiency, power and fluctuations are valid even when time-reversal symmetry is broken, revealing how such a symmetry breaking alters the fundamental constraints on steady-state energy conversion. Our results extend and refine previously established universal trade-offs, offering deeper insight into the performance limits in nonequilibrium thermodynamics. Guided by this bound, heat engines with broken time-reversal symmetry can be operated at near-Carnot efficiency while maintaining finite power output and fluctuations, enabling them to outperform their traditional counterparts.

cond-mat.stat-mech↗

arXiv2026

Fluctuation-Dissipation Limits in Quantum Thermoelectric Transport

As a fundamental measure of stability in nonequilibrium thermodynamics, fluctuations provide critical insight into the performance and reliability of heat engines. In this work, we establish universal fluctuation-dissipation bounds that directly link energy-current fluctuations to both the entropy production rate and steady-state transport currents. Our results are applicable to arbitrary temperature and chemical potential gradients and hold for all steady states within the framework of quantum scattering theory. These bounds remain robust even in regimes where quantum effects break classical thermodynamic uncertainty relations. We demonstrate their validity by using boxcar transmission functions and further derive constraints on the power output from the perspective of fluctuations and dissipation, offering a unified thermodynamic guideline for the design and evaluation of nanoscale and quantum thermal devices.

cond-mat.stat-mech↗

arXiv2025

Quantum Coherence as a Thermodynamic Resource Beyond the Classical Uncertainty Bound

Thermodynamic uncertainty relations (TURs) establish a fundamental trade-off between current precision and entropy production in nonequilibrium systems, yet the role of genuine quantum coherence in these bounds remains unresolved. Here we develop a general framework that explicitly incorporates quantum coherence into TURs for Markovian open quantum systems. By combining the quantum Cram\'er-Rao inequality with a Dyson series expansion of the parametrically deformed Lindblad dynamics, we derive a generalized TUR containing a coherence-sensitive correction that naturally separates classical and quantum contributions. The coherent term originates from the off-diagonal components of the nonequilibrium steady-state density matrix and systematically relaxes the classical precision-dissipation bound, allowing enhanced current precision without additional entropy production. Applying our theory to a three-level quantum maser, we demonstrate that steady-state coherence enables precision beyond the classical limit over a broad parameter regime while remaining consistent with the generalized bound. Our results identify quantum coherence as a genuine thermodynamic resource and provide a unified framework bridging classical and quantum uncertainty relations.

quant-ph↗

arXiv2025

Unlocking inaccessible performance of the quantum refrigerator with catalysts

Quantum thermal machines offer promising platforms for exploring the fundamental limits of thermodynamics at the microscopic scale. The previous study demonstrated that the incorporation of a catalyst can significantly enhance the performance of a heat engine by broadening its operational regime and achieving a more favorable trade-off between work output and efficiency. Building on this powerful framework and innovative idea, here we further extend the concept to a two-stroke quantum refrigerator that extracts heat from a cold reservoir via discrete strokes powered by external work. The working medium consists of two two-level systems (TLSs) and two heat reservoirs at different temperatures and is assisted by an auxiliary system acting as a catalyst. Remarkably, the catalyst remains unchanged after each cycle, ensuring that heat extraction is driven entirely by the work input. We show that the presence of the catalyst leads to two significant enhancements: it enables the coefficient of performance (COP) and cooling capacity to exceed the Otto bound and allows the refrigerator to operate in frequency and temperature regimes that are inaccessible without a catalyst. Furthermore, through a comparison with catalytic heat engines, our analysis reveals that two distinct permutation types are necessary to simultaneously enhance the COP and operational range of refrigerators, in contrast to heat engines for which a single permutation suffices. These results highlight the potential of catalytic mechanisms to broaden the operational capabilities of quantum thermal devices and to surpass conventional thermodynamic performance limits.

quant-ph↗

arXiv2025

Performance optimization of Nernst-based thermionic engines

In this paper, we examine the power and efficiency of the thermionic device utilizing the Nernst effect, with a specific focus on its potential application as an engine. The device operates by utilizing the vertical heat current to generate a horizontal particle current against the chemical potential. By considering the influence of a strong magnetic field, we derive analytical expressions for the current and heat flux. These expressions are dependent on the temperature and chemical potential of heat reservoirs, providing valuable insights into the device performance. The impact of driving temperatures on the performance of the thermionic engine has been assessed through numerical analysis. The research findings will guide the experimental design of Nernst-based thermionic engines.

cond-mat.stat-mech↗

arXiv2024

Hot-carrier photocatalysts with energy-selective contacts based on quantum wells and dots

In this paper, we simulate the function of hot-carrier photocatalysts (HCPCs) with quantum well and quantum dot energy-selective contacts (ESCs) in the water-splitting reaction. The transport equations for these ESCs are derived by using ballistic transport theory. The results indicate that thermalization loss from non-ideal ESCs is a primary factor diminishing the efficiency of HCPCs. The performance of HCPCs can be enhanced by optimizing the position of ESCs and the width of the extraction energy. Notably, HCPCs with quantum dot ESCs demonstrate superior performance compared to those with quantum well ESCs.

physics.app-ph↗

arXiv2024

The effect of space charge on photon-enhanced thermionic emission in the presence of the bidirectional discharge

The bidirectional space charge effects in photon-enhanced thermionic emission (PETE) devices are investigated systematically. First, we precisely determine the carrier concentrations and cathode temperatures by taking into account the electron recycling effect, energy balance constraints, and space charge effects arising from the concurrent discharge of the cathode and anode. Next, we analyze the impact of critical parameters, including anode properties and operating conditions, on the space charge barrier distribution and the overall performance of the device. The results demonstrate that the impact of reverse discharge on the net current becomes more pronounced when the PETE device operates at high anode temperatures, low anode work functions, and with a moderate solar concentration ratio and gap width. This discovery not only deepens our understanding of the bidirectional space charge effect, but also provides valuable guidance for the future optimization of PETE device performance.

physics.acc-ph↗

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↗

arXiv2022

Theoretical bound of the efficiency of learning

A unified thermodynamic formalism describing the efficiency of learning is proposed. First, we derive an inequality, which is more strength than Clausius's inequality, revealing the lower bound of the entropy-production rate of a subsystem. Second, the inequality is transformed to determine the general upper limit for the efficiency of learning. In particular, we exemplify the bound of the efficiency in nonequilibrium quantum-dot systems and networks of living cells. The framework provides a fundamental trade-off relationship between energy and information inheriting in stochastic thermodynamic processes.

cond-mat.stat-mech↗