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Shanhe Su

Publications and source records attributed to Shanhe Su.

At least 19 recordsLinked to original sources
arXiv2026

Versatile probe state preparation via generalized measurements for quantum sensing and thermometry

We investigate a probe state preparation protocol based on two non-selective generalized quantum measurements to enhance parameter estimation in single-qubit systems. By fine-tuning the measurement strengths, we demonstrate the ability to design a broad class of probe states, initially prepared in a thermal state, which can be optimized for specific estimation tasks. We apply this framework to characterize the decay rate and the temperature of a generalized amplitude damping channel. Our results show that the preparation protocol significantly modulates the quantum Fisher information for both parameters. Furthermore, we derive a general analytical relationship between the quantum Fisher information, thermodynamic susceptibilities, and Hamiltonian variance, valid even in the transient regime. This connection highlights the role of energy fluctuations and kinetic response in determining metrological precision. Finally, we briefly discuss a quantum circuit for experimental implementation using nuclear magnetic resonance techniques.

quant-ph↗
arXiv2026

Large Deviation Functions for Open Quantum Systems with a Strong Symmetry

In open quantum systems with strong symmetries, the global scaled cumulant generating function (SCGF) is generally nonanalytic, so the G\"artner-Ellis theorem cannot directly yield the genuine large-deviation rate function. To address this issue, we propose that the theorem remains valid within blocks of the systems' operator space: we first obtain local rate functions for each block via the theorem and then recover the global one by minimization. This approach is justified by the dissipative freezing phenomenon in such systems. We demonstrate the scheme in an analytical model and a three-spin model with XX interaction. In the latter, we find that the vanishing of a nonanalytic point in the global SCGF under dephasing appears as an avoided ``level'' crossing, and we quantify this behavior using a degenerate perturbation theory.

cond-mat.stat-mech↗
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

Non-monotonic Irreversibility in Polytropic Steering

The efficient manipulation of thermodynamic states within the finite time is fundamentally constrained by the intrinsic dissipative cost. While the slow-driving regime is well-characterized by a universal $1/\tau$-scaling of irreversibility, the physics governing fast, non-adiabatic transitions remains elusive. Here, we propose the polytropic steering protocols that provide an exact analytical bridge between the isothermal and adiabatic limits for Brownian particles far-from-equilibrium. We demonstrate that for any protocol duration $\tau$, the system can be precisely steered along a prescribed polytropic trajectory, revealing a striking non-monotonic dependence of irreversibility on the driving rate. Contrary to the near-equilibrium paradigm where faster driving necessitates higher energetic costs, we identify a most-irreversible timescale, beyond which dissipation is anomalously suppressed by rapid driving. By mapping these protocols onto a broad class of controllable thermodynamic cycle, we establish power-efficiency tradeoffs and position the polytropic index as a genuine thermodynamic control knob for the rational design of high-speed, high-performance microscopic thermal machines.

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

Geometric Bound for Trade-off Relation in Quantum Tricycle

We establish a finite-time quantum tricycle driven by an external field and investigate its thermodynamic performance in the slow-driving regime. By developing a perturbative expansion of heat with respect to operation time, we capture the dynamics of heat exchange processes beyond the quasistatic limit. Within a geometric framework, we derive fundamental bounds on trade-offs between the cooling rate, coefficient of performance, and dissipation, governed by the thermodynamic length and trajectory geometry in control space. Our findings unveil intrinsic limits to the performance of quantum thermal machines and highlight the role of geometry in shaping finite-time thermodynamics. This work advances the fundamental understanding of quantum thermodynamic processes and offers guiding principles for the design of next-generation quantum technologies.

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↗
arXiv2025

Thermodynamic uncertainty relations for multi-terminal systems with broken time-reversal symmetry

We investigate the thermodynamic uncertainty relations (TURs) in steady-state transport for a multi-terminal system consisting of two conducting terminals and N-2 probe terminals, within the linear response regime under broken time-reversal symmetry. We independently derive exact bounds on the TURs for the steady-state particle and heat currents under a strong constraint on the Onsager coefficients. Based on our proposed exact bounds, the analysis reveals that the bounds differ for particle and heat currents and are dependent on the system parameters. Furthermore, we demonstrate that under specific parameter conditions, the TURs of the particle and heat currents have a unified minimum value that depends solely on the number of terminals.

cond-mat.stat-mech↗
arXiv2025

Optimal neutralization of negative space charges in photon-enhanced thermionic emission devices under bidirectional discharge

In this study, we innovatively modeled photon-enhanced thermionic emission (PETE) devices, incorporating positive ion injection and bidirectional discharge's effects on the space charge barrier simultaneously. Compared to previous models, our model allows the positive ion distribution function to be compatible with scenarios in which the anode motive is either higher or lower than the cathode motive, and also adapts to significant anode discharge. Through numerical simulations and parametric analyses, we found that: (1) As the ratio of the positive ion increases, the capability for space charge neutralization becomes stronger. (2) The lower the electron affinity is, the smaller the ratio of positive ions are required. (3) When the anode temperature is higher or the anode work function is lower, the impact of reverse discharge on the net current density is more pronounced. Conversely, when the anode temperature is higher or the anode work function is greater, the ratio of positive ions required to achieve complete space charge neutralization increases. This study further elucidates the mechanisms and characteristics of space charge neutralization effects in PETE devices, providing a theoretical foundation for optimizing their design. Additionally, the accompanying theory and algorithm possess the potential to spark innovative research across diverse fields.

physics.acc-ph↗
arXiv2025

Centenary progress from the Nernst theorem to the Nernst statement

It is found from textbooks that there are the different versions of the schematic diagram related to the Nernst equation, and consequently, it leads to some discussion related to the Nernst equation and the discovery of other meaningful schematic diagrams never appearing in literature. It is also found that through the introduction of a new function, the schematic diagram of the Nernst equation in the isothermal process of any thermodynamic system can be generated in a unified way and that the Nernst equation can be re-obtained from the experimental data of low-temperature chemical reactions without any artificial additional assumptions. The results obtained here show clearly that the centenary progress from the Nernst theorem to the Nernst statement is completed.

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

Performance optimization of a finite-time quantum tricycle

We establish a finite-time external field-driven quantum tricycle model. Within the framework of slow driving perturbation, the perturbation expansion of heat in powers of time can be derived during the heat exchange processes. Employing the method of Lagrange multiplier, we optimize the cooling performance of the tricycle by considering the cooling rate and the figure of merit, which is the product of the coefficient of performance and cooling rate, as objective functions. Our findings reveal the optimal operating region of the tricycle, shedding light on its efficient performance.

quant-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↗
arXiv2024

Semi-Markov Processes in Open Quantum Systems. III. Large Deviations of First Passage Time Statistics

In a specific class of open quantum systems with finite and fixed numbers of collapsed quantum states, the semi-Markov process method is used to calculate the large deviations of the first passage time statistics. The core formula is an equation of poles, which is also applied in determining the scaled generating functions (SCGFs) of the counting statistics. For simple counting variables, the SCGFs of the first passage time statistics are derived by finding the largest modulus of the roots of this equation with respect to the $z$-transform parameter and then calculating its logarithm. The procedure is analogous to that of solving for the SCGFs of the counting statistics. However, for current-like variables, the method generally fails unless the equation of pole is simplified to a quadratic form. The fundamental reason for this lies in the nonuniqueness between the roots and the region of convergence for the joint transform. We illustrate these results via a resonantly driven two-level quantum system, where for several counting variables the solutions to the SCGFs of the first passage time are analytically obtained. Furthermore, we apply these functions to investigate quantum violations of the classical kinetic and thermodynamic uncertainty relations.

cond-mat.stat-mech↗