The Experts below are selected from a list of 62277 Experts worldwide ranked by ideXlab platform
Jincan Chen - One of the best experts on this subject based on the ideXlab platform.
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performance analysis of an irreversible quantum heat engine working with Harmonic Oscillators
Physical Review E, 2003Co-Authors: Bihong Lin, Jincan ChenAbstract:The cycle model of a regenerative quantum heat engine working with many noninteracting Harmonic Oscillators is established. The cycle consists of two isothermal and two constant-frequency processes. The performance of the cycle is investigated, based on the quantum master equation and semigroup approach. The inherent regenerative losses in the two constant-frequency processes are calculated. The expressions of several important performance parameters such as the efficiency, power output, and rate of the entropy production are derived for several interesting cases. Especially, the optimal performance of the cycle in high-temperature limit is discussed in detail. The maximum power output and the corresponding parameters are calculated. The optimal region of the efficiency and the optimal ranges of the temperatures of the working substance in the two isothermal processes are determined.
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The optimal performance of a quantum refrigeration cycle working with Harmonic Oscillators
Journal of Physics D, 2003Co-Authors: Jincan ChenAbstract:The cycle model of a quantum refrigeration cycle working with many non-interacting Harmonic Oscillators and consisting of two isothermal and two constant-frequency processes is established. Based on the quantum master equation and semi-group approach, the general performance of the cycle is investigated. Expressions for some important performance parameters, such as the coefficient of performance, cooling rate, power input, and rate of the entropy production, are derived. Several interesting cases are discussed and, especially, the optimal performance of the cycle at high temperatures is discussed in detail. Some important characteristic curves of the cycle, such as the cooling rate versus coefficient of performance curves, the power input versus coefficient of performance curves, the cooling rate versus power input curves, and so on, are presented. The maximum cooling rate and the corresponding coefficient of performance are calculated. Other optimal performances are also analysed. The results obtained here are compared with those of an Ericsson or Stirling refrigeration cycle using an ideal gas as the working substance. Finally, the optimal performance of a Harmonic quantum Carnot refrigeration cycle at high temperatures is derived easily.
M A Rajabpour - One of the best experts on this subject based on the ideXlab platform.
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bipartite entanglement entropy of the excited states of free fermions and Harmonic Oscillators
Physical Review B, 2019Co-Authors: Arash Jafarizadeh, M A RajabpourAbstract:We study general entanglement properties of the excited states of the one-dimensional translational invariant free fermions and coupled Harmonic Oscillators. In particular, using the integrals of motion, we prove that these Hamiltonians independent of the gap (mass) have infinite excited states that can be described by conformal field theories with integer or half-integer central charges. In the case of free fermions, we also show that because of the huge degeneracy in the spectrum, even a gapless Hamiltonian can have excited states with an area law. Finally, we study the universal average entanglement entropy over eigenstates of the Hamiltonian of the free fermions introduced recently in Vidmar et al. [Phys. Rev. Lett. 119, 020601 (2017)]. In particular, using a duality relation, we map the average bipartite entanglement entropy over all the exponential numbers of eigenstates of a generic free fermion Hamiltonian to the problem of the calculation of the average multibipartite entanglement entropy over a single eigenstate of the $\mathit{XX}$ chain. This relation can be useful for experimental measurement of the universal average entanglement entropy. Part of our conclusions can be extended to the quantum spin chains that are associated with the free fermions via Jordan-Wigner transformation.
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entanglement dynamics in short and long range Harmonic Oscillators
Physical Review B, 2014Co-Authors: Ghasemi M Nezhadhaghighi, M A RajabpourAbstract:We study the time evolution of the entanglement entropy in the short- and long-range-coupled Harmonic Oscillators that have well-defined continuum limit field theories. We first introduce a method to calculate the entanglement evolution in generic coupled Harmonic Oscillators after quantum quench. Then we study the entanglement evolution after quantum quench in Harmonic systems in which the couplings decay effectively as $1/{r}^{d+\ensuremath{\alpha}}$ with the distance $r$. After quenching the mass from a nonzero value to zero we calculate numerically the time evolution of von Neumann and R\'enyi entropies. We show that for $1l\ensuremath{\alpha}l2$ we have a linear growth of entanglement and then saturation independent of the initial state. For $0l\ensuremath{\alpha}l1$ depending on the initial state we can have logarithmic growth or just fluctuation of entanglement. We also calculate the mutual information dynamics of two separated individual Harmonic Oscillators. Our findings suggest that in our system there is no particular connection between having a linear growth of entanglement after quantum quench and having a maximum group velocity or generalized Lieb-Robinson bound.
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quantum entanglement entropy and classical mutual information in long range Harmonic Oscillators
Physical Review B, 2013Co-Authors: Ghasemi M Nezhadhaghighi, M A RajabpourAbstract:We study different aspects of quantum von Neumann and R\'enyi entanglement entropy of one-dimensional long-range Harmonic Oscillators that can be described by well-defined nonlocal field theories. We show that the entanglement entropy of one interval with respect to the rest changes logarithmically with the number of Oscillators inside the subsystem. This is true also in the presence of different boundary conditions. We show that the coefficients of the logarithms coming from different boundary conditions can be reduced to just two different universal coefficients. We also study the effect of the mass and temperature on the entanglement entropy of the system in different situations. The universality of our results is also confirmed by changing different parameters in the coupled Harmonic Oscillators. We also show that more general interactions coming from general singular Toeplitz matrices can be decomposed to our long-range Harmonic Oscillators. Despite the long-range nature of the couplings, we show that the area law is valid in two dimensions and the universal logarithmic terms appear if we consider subregions with sharp corners. Finally, we study analytically different aspects of the mutual information such as its logarithmic dependence to the subsystem, effect of mass, and influence of the boundary. We also generalize our results in this case to general singular Toeplitz matrices and higher dimensions.
Peter Salamon - One of the best experts on this subject based on the ideXlab platform.
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thermodynamical analysis of a quantum heat engine based on Harmonic Oscillators
Physical Review E, 2016Co-Authors: Andrea Insinga, Bjarne Andresen, Peter SalamonAbstract:Many models of heat engines have been studied with the tools of finite-time thermodynamics and an ensemble of independent quantum systems as the working fluid. Because of their convenient analytical properties, Harmonic Oscillators are the most frequently used example of a quantum system. We analyze different thermodynamical aspects with the final aim of the optimization of the performance of the engine in terms of the mechanical power provided during a finite-time Otto cycle. The heat exchange mechanism between the working fluid and the thermal reservoirs is provided by the Lindblad formalism. We describe an analytical method to find the limit cycle and give conditions for a stable limit cycle to exist. We explore the power production landscape as the duration of the four branches of the cycle are varied for short times, intermediate times, and special frictionless times. For short times we find a periodic structure with atolls of purely dissipative operation surrounding islands of divergent behavior where, rather than tending to a limit cycle, the working fluid accumulates more and more energy. For frictionless times the periodic structure is gone and we come very close to the global optimal operation. The global optimum is found and interestingly comes with a particular value of the cycle time.
Ghasemi M Nezhadhaghighi - One of the best experts on this subject based on the ideXlab platform.
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entanglement dynamics in short and long range Harmonic Oscillators
Physical Review B, 2014Co-Authors: Ghasemi M Nezhadhaghighi, M A RajabpourAbstract:We study the time evolution of the entanglement entropy in the short- and long-range-coupled Harmonic Oscillators that have well-defined continuum limit field theories. We first introduce a method to calculate the entanglement evolution in generic coupled Harmonic Oscillators after quantum quench. Then we study the entanglement evolution after quantum quench in Harmonic systems in which the couplings decay effectively as $1/{r}^{d+\ensuremath{\alpha}}$ with the distance $r$. After quenching the mass from a nonzero value to zero we calculate numerically the time evolution of von Neumann and R\'enyi entropies. We show that for $1l\ensuremath{\alpha}l2$ we have a linear growth of entanglement and then saturation independent of the initial state. For $0l\ensuremath{\alpha}l1$ depending on the initial state we can have logarithmic growth or just fluctuation of entanglement. We also calculate the mutual information dynamics of two separated individual Harmonic Oscillators. Our findings suggest that in our system there is no particular connection between having a linear growth of entanglement after quantum quench and having a maximum group velocity or generalized Lieb-Robinson bound.
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quantum entanglement entropy and classical mutual information in long range Harmonic Oscillators
Physical Review B, 2013Co-Authors: Ghasemi M Nezhadhaghighi, M A RajabpourAbstract:We study different aspects of quantum von Neumann and R\'enyi entanglement entropy of one-dimensional long-range Harmonic Oscillators that can be described by well-defined nonlocal field theories. We show that the entanglement entropy of one interval with respect to the rest changes logarithmically with the number of Oscillators inside the subsystem. This is true also in the presence of different boundary conditions. We show that the coefficients of the logarithms coming from different boundary conditions can be reduced to just two different universal coefficients. We also study the effect of the mass and temperature on the entanglement entropy of the system in different situations. The universality of our results is also confirmed by changing different parameters in the coupled Harmonic Oscillators. We also show that more general interactions coming from general singular Toeplitz matrices can be decomposed to our long-range Harmonic Oscillators. Despite the long-range nature of the couplings, we show that the area law is valid in two dimensions and the universal logarithmic terms appear if we consider subregions with sharp corners. Finally, we study analytically different aspects of the mutual information such as its logarithmic dependence to the subsystem, effect of mass, and influence of the boundary. We also generalize our results in this case to general singular Toeplitz matrices and higher dimensions.
Stefano Olla - One of the best experts on this subject based on the ideXlab platform.
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kinetic limit for a chain of Harmonic Oscillators with a point langevin thermostat
Journal of Functional Analysis, 2020Co-Authors: Tomasz Komorowski, Stefano OllaAbstract:Abstract We consider an infinite chain of coupled Harmonic Oscillators whose Hamiltonian dynamics is perturbed by a random exchange of momentum between particles such that total energy and momentum are conserved, modeling collision between atoms. This random exchange is rarefied in the limit, that corresponds to the hypothesis that in the macroscopic unit time only a finite number of collisions takes place (the Boltzmann-Grad limit). Furthermore, the system is in contact with a Langevin thermostat at temperature T through a single particle. We prove that, after the hyperbolic space-time rescaling, the Wigner distribution, describing the energy density of phonons in space-frequency domain, converges to a positive energy density function W ( t , y , k ) that evolves according to a linear kinetic equation, with the interface condition at y = 0 that corresponds to reflection, transmission and absorption of phonons caused by the presence of the thermostat. The paper extends the results of [15] , where a Harmonic chain (with no inter-particle scattering) in contact with a Langevin thermostat has been considered.
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High frequency limit for a chain of Harmonic Oscillators with a point Langevin thermostat
Archive for Rational Mechanics and Analysis, 2020Co-Authors: Tomasz Komorowski, Stefano Olla, Lenya Ryzhik, Herbert SpohnAbstract:We consider an infinite chain of coupled Harmonic Oscillators with a Langevin thermostat at the origin. In the high frequency limit, we establish the reflection-transmission coefficients for the wave energy for the scattering of the thermostat. To our surprise, even though the thermostat fluctuations are time-dependent, the scattering does not couple wave energy at various frequencies.
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Kinetic limit for a chain of Harmonic Oscillators with a point Langevin thermostat
Journal of Functional Analysis, 2020Co-Authors: Tomasz Komorowski, Stefano OllaAbstract:We consider an infinite chain of coupled Harmonic Oscillators with a Langevin thermostat attached at the origin and energy, momentum and volume conserving noise that models the collisions between atoms. The noise is rarefied in the limit, that corresponds to the hypothesis that in the macroscopic unit time only a finite number of collisions takes place (Boltzmann-Grad limit). We prove that, after the hyperbolic space-time rescaling, the Wigner distribution, describing the energy density of phonons in space-frequency domain, converges to a positive energy density function W (t, y, k) that evolves according to a linear kinetic equation, with the interface condition at y = 0 that corresponds to reflection, transmission and absorption of phonons. The paper extends the results of [3], where a thermostatted Harmonic chain (with no inter-particle scattering) has been considered.
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superdiffusion of energy in a chain of Harmonic Oscillators with noise
Communications in Mathematical Physics, 2015Co-Authors: Milton Jara, Tomasz Komorowski, Stefano OllaAbstract:We consider a one dimensional infinite chain of Harmonic Oscillators whose dynamics is perturbed by a stochastic term conserving energy and momentum. We prove that in the unpinned case the macroscopic evolution of the energy converges to the solution of the fractional diffusion equation \({\partial_t u = -|\Delta|^{3/4}u}\). For a pinned system we prove that its energy evolves diffusively, generalizing some results of Basile and Olla (J. Stat. Phys. 155(6):1126–1142, 2014).
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SUPERDIFFUSION OF ENERGY IN A CHAIN OF Harmonic Oscillators WITH NOISE
Communications in Mathematical Physics, 2015Co-Authors: Milton Jara, Tomasz Komorowski, Stefano OllaAbstract:We consider a one dimensional infinite chain of Harmonic Oscillators whose dynamics is perturbed by a stochastic term conserving energy and momentum. We prove that in the unpinned case the macroscopic evolution of the energy converges to the solution of the fractional diffusion equation ∂ t u = −|∆| 3/4 u. For a pinned system we prove that its energy evolves diffusively, generalizing some results of [4].
