arXiv subjects

Jincan Chen

Publications and source records attributed to Jincan Chen.

At least 37 records · Page 2Linked to original sources

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

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

Thermometry based on Coulomb-coupled quantum dots

A theoretical proposal that Coulomb-coupled quantum dots can be used as quantum probes to determine the temperature of a sample (i.e., an electronic reservoir) is proposed. Through the regulation of the positive or negative voltage bias in the thermometer, we are able to judge whether the temperature of the sample is higher or lower than that of the reference heat reservoir in the measure environment and to determine the precise temperature of the sample by using a particularly simple temperature-voltage bias relationship in the reversible condition. One outstanding characteristic of the thermometer is that when the sample is at low temperatures, a small temperature change will lead to a large voltage bias change. It means that the proposed thermometer has a high sensitivity when low-temperature samples are measured.

cond-mat.mes-hall↗

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↗

arXiv2017

Coulomb-coupled quantum-dot thermal transistors

A quantum-dot thermal transistor consisting of three Coulomb-coupled quantum dots coupled to respective electronic reservoirs by tunnel contacts is established. The heat flows through the collector and emitter can be controlled by the temperature of the base. It is found that a small change in the base heat flow can induce a large heat flow change in the collector and emitter. The huge amplification factor can be obtained by optimizing the Coulomb interaction between the collector and the emitter or by decreasing the energy-dependent tunneling rate at the base. The proposed quantum-dot thermal transistor may open up potential applications in low-temperature solid-state thermal circuits at the nanoscale.

physics.app-ph↗

arXiv2017

Resonant current in coupled inertial Brownian particles with delayed-feedback control

The transport of a walker in rocking feedback-controlled ratchets are investigated. The walker consists of two coupled "feet" that allow the interchange of the order of the particles while the walker moves. In the underdamped case, the deterministic dynamics of the walker in a tilted asymmetric ratchet with an external periodic force is considered. It is found that the delayed feedback ratchets with a switching-on-and-off dependence of the states of the system can lead to the absolute negative mobility (ANM). In such a novel phenomenon the particles move against the bias. Moreover, the walker can acquire a series of resonant steps for different values of the current. Remarkably, it is interesting to find that the resonant current of the walker are induced by the phase locked motion that corresponds to the synchronization of the motion with the change in the frequency of the external driving. These resonant steps can be well predicted in terms of time-space symmetry analysis, which is in good agreement with dynamics simulations. The transport performances can be optimized and furthermore controlled by suitably adjusting the parameters of the delayed-feedback ratchets.

cond-mat.stat-mech↗

arXiv2016

The internal energy expression of a long-range interaction complex system and its statistical physical properties

Considering the interactions of two arbitrary particles, we obtain an internal energy expression of the complex system having long-range interactions. Based on the postulate of "equal-probability principle" for all microstates, the probability distribution function of the system is derived, and consequently, some main statistical physical properties of the system are revealed. It is important to find that the properties of a long-range interaction system are very closely dependent on the interaction coefficient and particle number.

cond-mat.stat-mech↗

arXiv2015

A statistical theory of complex systems

Based on the probability distribution observed in complex systems and an assumption that the probability distributions of complex systems satisfy a new generalized multiplication, it is proved that the statistical theory of complex systems can be established in the analogous extensive framework.

cond-mat.stat-mech↗

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↗

arXiv2013

Conditional statistical properties of the complex systems having long-range interactions

A new concept of the available force is proposed to investigate the performance of the complex systems having long-range interactions. Since the covariance of average velocity in double time interval and available force equals zero, it is possible to calculate the conditional probability distribution function (CPDF) within the systems. It is found that the asymmetric CPDF of the velocity between two adjacent time intervals can be derived from the symmetrical CPDF between the available force and the double time interval velocity. Two typical currency exchange databases, i.e., EUR/USD and GBP/USD, which collect the minutely opening exchange prices from 1 January 1999 to 31 December 2011, are adopted as examples. It is found that the analytical CPDF needs only six parameters for an arbitrary system. By calculating the CPDF in the currency exchange databases, it is shown that the results are well fitted by our analytical expression. The analytical CPDF can be also used to calculate the conditional expectation and the conditional variance of velocity. Interestingly, the two databases show that the conditional expectation of the velocity between two adjacent time intervals is not monotonic, while the conditional variance tends to monotonic. All of these results are well described by our theory. It is worthwhile to note that the analytical CPDF is a general expression. It is valid not only for current exchange systems but also for any complex systems having long-range interactions and/or long-duration memory.

cond-mat.stat-mech↗

arXiv2013

The available force in long-range interaction complex systems and its statistical physical properties

A new concept of the available force in long-range interaction complex systems is proposed. The relationship between the available force in different time intervals and the interaction parameters of complex systems is described. It is found that when the interaction parameters satisfy a determined condition, the trajectory that the velocity is divergent but the displacement is convergent can be well described and that the long-range interaction, anomalous diffusion, and q-Gaussian type distribution of complex systems can also be well described by the interaction parameters in different cases. In addition, by utilizing the velocity of time series randomly and analyzing its probability distribution of displacement, it is explained that when there exists the long-range interaction in complex systems, the fat-tail distributions will exhibit. The results obtained show that the relationship between the available force and the interaction parameters may be used to investigate the statistical physical properties in long-range interaction complex systems.

cond-mat.stat-mech↗