arXiv subjects

Jizhou He

Publications and source records attributed to Jizhou He.

17 recordsLinked to original sources

arXiv2024

Giant enhancement of the transverse magneto-optical Kerr effect in etchless bismuth-substituted yttrium iron garnet empowered by quasi-bound states in the continuum

Here, we propose an etchless bismuth-substituted yttrium iron garnet layer assisted by a one-dimensional resonant grating waveguide to enhance transverse magneto-optical Kerr effect (TMOKE) via the excitation of quasi-bound state in the continuum. The TMOKE amplitude can be tailored by manipulating the perturbation parameter, and it can reach as high as 1.978, approaching the theoretical maximum value of 2. Additionally, a single-mode temporal coupled-mode theory is employed to further reveal the underlying physical mechanism. It is found that TMOKE is strongly related to the line width of the quasi-BIC resonance and local field enhancement, which are pivotal factors in the design and optimization of photonic devices. As a potential application, we design and numerically demonstrate a refractive index sensor based on the resonantly enhanced TMOKE, with the optimal sensitivity of 110.66 nm/RIU and the corresponding maximum figure of merit of 299.3 RIU$^{-1}$. Our work provides a simple and efficient approach for enhancing TMOKE based on an easy-to-fabricate platform, laying the groundwork for exploring and developing magneto-optical devices such as sensors, magnetic storage devices, and nonreciprocal photonic devices.

physics.optics↗

arXiv2023

Thermodynamics and Fluctuations in Quantum Heat Engines under Reservoir Squeezing

We investigate the thermodynamics and fluctuations of a finite-time quantum Otto engine alternatively driven by a hot squeezed and a cold thermal reservoir. We show that reservoir squeezing significantly enhances the performance by increasing the thermodynamic efficiency and the power, and enables higher stability by decreasing the relative power fluctuations and speeding up the convergence of quantum efficiency to its most probable value. These results are explained by our theoretical analysis that incorporates the effect of reservoir squeezing on the irreversibility associated with quantum friction and coherence due to finite time. An experimental scheme for realizing this quantum heat engine is proposed using a single-electron spin pertaining to a trapped 40Ca$^+$ ion. We provide a general framework for reliably studying the finite-time quantum heat engine and derive important insights into the novel thermodynamic behaviors beyond the classical thermal machines.

quant-ph↗

arXiv2023

Enhancing Faraday and Kerr rotations based on toroidal dipole mode in an all-dielectric magneto-optical metasurface

The magneto-optical Faraday and Kerr effects are widely used in modern optical devices. In this letter, we propose an all-dielectric metasurface composed of perforated magneto-optical thin films, which can support the highly confined toroidal dipole resonance and provide full overlap between the localized electromagnetic field and the thin film, and consequently enhance the magneto-optical effects to an unprecedented degree. The numerical results based on finite element method show that the Faraday and Kerr rotations can reach -13.59${\deg}$ and 8.19${\deg}$ in the vicinity of toroidal dipole resonance, which are 21.2 and 32.8 times stronger than those in the equivalent thickness of thin films, respectively. In addition, we design an environment refractive index sensor based on the resonantly enhanced Faraday and Kerr rotations, with sensitivities of 62.96 nm/RIU and 73.16 nm/RIU, and the corresponding maximum figures of merit 132.22${\deg}$/RIU and 429.45${\deg}$/RIU, respectively. This work provides a new strategy for enhancing the magneto-optical effects at nanoscale, and paves the way for the research and development of magneto-optical metadevices such as sensors, memories, and circuits.

physics.optics↗

arXiv2022

Quantum Otto engine with quantum correlations

We theoretically prose and investigate a photo-Otto engine that is working with a single-mode radiation field inside an optical cavity and alternatively driven by a hot and a cold reservoir, where the hot reservoir is realized by sending one of a pair of correlated two-level atoms to pass through the optical cavity, and the cold one is made of a collection of noninteracting boson modes. In terms of the quantum discord of the pair of atoms, we derive the analytical expressions for the performance parameters (power and efficiency) and stability measure (coefficient of variation for power). We show that quantum discord boosts the performance and efficiency of the quantum engine, and even may change the operation mode. We also demonstrate that quantum discord improves the stability of machine by decreasing the coefficient of variation for power which satisfies the generalized thermodynamic uncertainty relation. Finally, we find that these results can be transferred to another photo-Otto engine model, where the optical cavity is alternatively coupled to a hot thermal bosonic bath and to a beam of pairs of the two correlated atoms that play the role of a cold reservoir.

quant-ph↗

arXiv2022

Finite-time quantum Otto engine with a squeezed thermal bath: Role of quantum coherence and squeezing in the performance and fluctuations

We consider a finite-time quantum Otto heat engine that consists of two isochoric (thermal-contact) process, where the system is alternatively coupled to a hot squeezed and a cold thermal reservoir, and two unitary driven strokes, where the system is isolated from these two baths and its von Neumann entropy keeps constant. Both quantum inner friction and coherence are generated along the driven stroke and coherence cannot be fully erased after the finite-time hot isochore. Using full counting statistics, we present the probability distribution functions of heat injection and total work per cycle, which are dependent on the time duration along each process. With these, we derive the analytical expressions for the thermodynamic quantities of the two-level heat engine, such as total work, thermodynamic efficiency, entropy production, and work fluctuations, in which effects of coherence, squeezing, inner friction and finite-time heat exchange are included. We then numerically determine the thermodynamic quantities and the fluctuations using the parameters employed in the experimental implementation. Our results clarify the role of coherence and squeezing in the performance and fluctuations in the quantum Otto engines.

quant-ph↗

arXiv2022

Quantum heat engine based on trapped Bose gases: Its maximum efficiency can approach the Carnot value at finite power

It was reported that, if and only if the specific heat, correlation length, and dynamical exponents $α, ν$ and $z$, fulfill the condition $α-zν>0$, the phase transitions can enable a quantum heat engine to approach Carnot efficiency at finite power. We start our analysis via a different approach in which the effects of interaction and fluctuations on the Hamiltonian of a trapped dilute Bose gas belonging to the same universality as $XY$ model. Based on models of quantum Otto heat engines, we find the general expression of the efficiency which includes the correction due to interaction and fluctuations at the critical point, and show that, near the Bose-Einstein-condensation point with $α-zν<0$, energy fluctuations could enable attaintment of the Carnot efficiency with nonvanishing power. Such quantum heat engines can also be realized by changing the shape of the trap confining the ideal and weakly interacting Bose gas during the adiabatic processes of the cycle. These quantum heat engines working with the trapped Bose gases, which are based on techniques of cooling Bose condensates and could be realizable at present technology.

cond-mat.stat-mech↗

arXiv2022

Performance of quantum heat engines via adiabatic deformation of potential

We present a quantum Otto engine model consisting of two isochoric and two adiabatic strokes, where the adiabatic expansion or compression is realized by adiabatically changing the shape of the potential. Here we show that such an adiabatic deformation may alter operation mode and enhance machine performance by increasing output work and efficiency, even with the advantage of decreasing work fluctuations. If the heat engine operates under maximal power by optimizing the control parameter, the efficiency shows certain universal behavior.

quant-ph↗

arXiv2020

Power Fluctuations of An Irreversible Quantum Otto Engine

We derive the general probability distribution function of stochastic work for quantum Otto engines in which both the isochoric and driving processes are irreversible due to finite time duration. The time-dependent power fluctuations, average power, and thermodynamic efficiency are explicitly obtained for a complete cycle operating with an analytically solvable two-level system. We show that, there is a trade-off between efficiency (or power) and power fluctuations.

cond-mat.stat-mech↗

arXiv2020

Quantum refrigerators in finite-time cycle duration

We derive cooling rate and coefficient of performance as well as their variances for a quantum Otto engine proceeding in finite-time cycle period. This machine consists of two driven strokes, where the system isolated from the heat reservoir undergoes finite-time unitary transformation, and two isochoric steps, where the finite-time system-bath interaction durations take the system away from the equilibrium even at the respective ends of the two stages. We explicitly calculate the statistics of cooling rate and coefficient of performance for the machine operating with an analytically solvable two-level system. We clarify the role of finite-time durations of four processes on the machine performance. We show that there is the trade-off between the performance parameter and its corresponding variance, thereby indicating that the cooling rate or coefficient of performance can be enhanced, but at the cost of increasing the corresponding fluctuations.

cond-mat.stat-mech↗

arXiv2018

Efficiency and power of minimally nonlinear irreversible heat engines with broken time-reversal symmetry

We study the minimally nonlinear irreversible heat engines in which the time-reversal symmetry for the systems may b e broken. The expressions for the power and the efficiency are derived, in which the effects of the nonlinear terms due to dissipations are included. We show that, as within the linear responses, the minimally nonlinear irreversible heat engines enable attainment of Carnot efficiency at positive power. We also find that the Curzon-Ahlborn limit imposed on the efficiency at maximum power can be overcomed if the time-reversal symmetry is broken.

cond-mat.stat-mech↗

arXiv2014

Coefficient of performance under maximum $χ$ criterion in a two-level atomic system as a refrigerator

A two-level atomic system as a working substance is used to set up a refrigerator consisting of two quantum adiabatic and two isochoric processes (two constant-frequency processes $ω_a$ and $ω_b$ with $ω_a<ω_b$), during which the two-level system is in contact with two heat reservoirs at temperatures $T_h$ and $T_c (<T_h)$. Considering finite-time operation of two isochoric processes, we derive analytical expressions for cooling rate $R$ and coefficient of performance (COP) $\varepsilon$. The COP at maximum $χ(= \varepsilon R)$ figure of merit is numerically determined, and it is proved to be in nice agreement with the so-called Curzon and Ahlborn COP $\varepsilon_{CA}=\sqrt{1+\varepsilon_C}-1$, where $\varepsilon_C=T_c/(T_h-T_c)$ is the Carnot COP. In the high-temperature limit, the COP at maximum $χ$ figure of merit, $\varepsilon^*$, can be expressed analytically by $\varepsilon^* = \varepsilon_+ \equiv (\sqrt{9+8\varepsilon_C}-3)/2$, which was derived previously as the upper bound of optimal COP for the low-dissipation or minimally nonlinear irreversible refrigerators. Within context of irreversible thermodynamics, we prove that the value of $\varepsilon_{+}$ is also the upper bound of COP at maximum $χ$ figure of merit when we regard our model as a linear irreversible refrigerator.

cond-mat.stat-mech↗

arXiv2014

Efficiency at maximum power of a quantum Otto engine: Both within finite-time and irreversible thermodynamics

We consider the efficiency at maximum power of a quantum Otto engine, which uses a spin or a harmonic system as its working substance and works between two heat reservoirs at constant temperatures $T_h$ and $T_c$ $ (<T_h)$. Although the spin-$1/2$ system behaves quite differently from the harmonic system in that they obey two typical quantum statistics, the efficiencies at maximum power based on these two different kinds of quantum systems are bounded from the upper side by the same expression of the efficiency at maximum power: $η_{mp}\leqη_+\equiv η_C^2/[η_C-(1-η_C)\ln(1-η_C)]$, with $η_C=1-T_c/T_h$ the Carnot efficiency, which displays the same universality of the CA efficiency $η_{CA}=1-\sqrt{1-η_C}$ at small relative temperature difference. Within context of irreversible thermodynamics, we calculate the Onsager coefficients and, we show that the value of $η_{CA}$ is indeed the upper bound of EMP for the Otto engines working in the linear-response regime.

cond-mat.stat-mech↗

arXiv2014

A theoretical study on the performances of thermoelectric heat engine and refrigerator with two-dimensional electron reservoirs

Theoretical thermoelectric nanophysics models of low-dimensional electronic heat engine and refrigerator devices, comprising two-dimensional hot and cold reservoirs and an interconnecting filtered electron transport mechanism have been established. The models were used to numerically simulate and evaluate the thermoelectric performance and energy conversion efficiencies of these low-dimensional devices, based on three different types of electron transport momentum-dependent filters, referred to herein as: kx, ky and kr filters. Assuming the Fermi-Dirac distribution of electrons, expressions for key thermoelectric performance parameters were derived for the resonant transport processes, in which the transmission of electrons has been approximated as a Lorentzian resonance function. Optimizations were carried out and the corresponding optimized design parameters have been determined, including but not limited to the universal theoretical upper bound of the efficiency at maximum power for heat engines, and the maximum coefficient of performance for refrigerators. From the results, it was determined that kr filter delivers the best thermoelectric performance, followed by the kx filter, and then the ky filter. For refrigerators with any one of three filters, an optimum range for the full width at half maximum of the transport resonance was found to be <2kT .

cond-mat.mtrl-sci↗

arXiv2013

Coefficient of performance for a low-dissipation Carnot-like refrigerator with nonadiabatic dissipation

We study the coefficient of performance (COP) and its bounds of the Canot-like refrigerator working between two heat reservoirs at constant temperatures $T_h$ and $T_c$, under two optimization criteria $χ$ and $Ω$. In view of the fact that an "adiabatic" process takes finite time and is nonisentropic, the nonadiabatic dissipation and the finite time required for the "adiabatic" processes are taken into account. For given optimization criteria, we find that the lower and upper bounds of the COP are the same as the corresponding ones obtained from the previous idealized models where any adiabatic process undergoes instantaneously with constant entropy. When the dissipations of two "isothermal" and two "adiabatic" processes are symmetric, respectively, our theoretical predictions match the observed COP's of real refrigerators more closely than the ones derived in the previous models, providing a strong argument in favor of our approach.

cond-mat.stat-mech↗

arXiv2013

Quantum-mechanical engine models and their efficiencies

Based on quantum thermodynamic processes, we make a quantum-mechanical (QM) extension of the typical heat engine cycles, such as the Carnot, Brayton, Otto, and Diesel cycles, etc. The temperature is not included in these QM engine cycles, as lies in the fact that the concept of energy is well-defined in quantum mechanics, temperature \emph{a priori} is not. These QM engine cycles are implemented by an ideal or interacting system with an arbitrary number of particles confined in an arbitrary power-law trap. As a result, a relation between the quantum adiabatic exponent and trap exponent is found. The efficiency of a given QM engine cycle is similar to that of its classical counterpart, thereby identifying the universality of the efficiency.

cond-mat.stat-mech↗

arXiv2012

Efficiency at maximum power output of an irreversible Carnot-like cycle with internally dissipative friction

We investigate the efficiency at maximum power of an irreversible Carnot engine performing finite-time cycles between two reservoirs at temperatures $T_h$ and $T_c$ $(T_c<T_h)$, taking into account of internally dissipative friction in two "adiabatic" processes. In the frictionless case, the efficiencies at maximum power output are retrieved to be situated between $η_{_C}/$ and $η_{_C}/(2-η_{_C})$, with $η_{_C}=1-T_c/{T_h}$ being the Carnot efficiency. The strong limits of the dissipations in the hot and cold isothermal processes lead to the result that the efficiency at maximum power output approaches the values of $η_{_C}/$ and $η_{_C}/(2-η_{_C})$, respectively. When dissipations of two isothermal and two adiabatic processes are symmetric, respectively, the efficiency at maximum power output is founded to be bounded between 0 and the Curzon-Ahlborn (CA) efficiency $1-\sqrt{1-η{_C}}$, and the the CA efficiency is achieved in the absence of internally dissipative friction.

cond-mat.stat-mech↗

arXiv2012

Efficiency at maximum power output of quantum heat engines under finite-time operation

We study the efficiency at maximum power, $η_m$, of irreversible quantum Carnot engines (QCEs) that perform finite-time cycles between a hot and a cold reservoir at temperatures $T_h$ and $T_c$, respectively. For QCEs in the reversible limit (long cycle period, zero dissipation), $η_m$ becomes identical to Carnot efficiency $η_{_C}=1-\frac{T_c}{T_h}$. For QCE cycles in which nonadiabatic dissipation and time spent on two adiabats are included, the efficiency $η_m$ at maximum power output is bounded from above by $\frac{η_{_C}}{2-η_{_C}}$ and from below by $\frac{η_{_C}}2$. In the case of symmetric dissipation, the Curzon-Ahlborn efficiency $η_{_{CA}}=1-\sqrt{\frac{T_c}{T_h}}$ is recovered under the condition that the time allocation between the adiabats and the contact time with the reservoir satisfy a certain relation.

cond-mat.stat-mech↗