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Non-equilibrium steady states for a Harmonic oscillator interacting with several Boson systems - Currents and Entropy production rate -

Tomohiro Kanda

Published Jan 28, 2018• 0 citations
OpenAlex

Abstract

Non-equilibrium steady states (NESS) of Boson systems with different phases are investigated with the aid of the C^*-algebraic method. The system consists of sample and several free or pure-hopping bosonic reservoirs coupled with each other. Initially, the sample and reservoirs are uncoupled and in equilibrium with temperatures, local densities, and phases. At t=0, the reservoirs couple with each other through the sample. NESS are constructed as time limit of the composition of initial state and time evolution of coupled system. In NESS, Josephson currents and the mean entropy production rates are calculated. The mean entropy production rate does not depend on phase differences. As consequence, the currents provided to phase differences produces no entropy.

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•Jan 1, 2005•7 citations
Non-equilibrium steady states (NESS) of Boson systems with different phases are investigated with the aid of the C^*-algebraic method. The system consists of sample and several free or pure-hopping bosonic reservoirs coupled with each other. Initially, the sample and reservoirs are uncoupled and in equilibrium with temperatures, local densities, and phases. At t=0, the reservoirs couple with each other through the sample. NESS are constructed as time limit of the composition of initial state and time evolution of coupled system. In NESS, Josephson currents and the mean entropy production rates are calculated. The mean entropy production rate does not depend on phase differences. As consequence, the currents provided to phase differences produces no entropy.
Non-equilibrium steady states, in the sense of Ruelle [Commun. Math. Phys. 224, 3–16 (2001)], of Boson systems with Bose–Einstein condensation are investigated with the aid of the C*-algebraic method. The model consists of a quantum particle and several bosonic reservoirs. We show that the mean entropy production rate is strictly positive and independent of phase differences provided that the temperatures or the chemical potentials of reservoirs are different. Moreover, Josephson currents occur without entropy production, if the temperatures and the chemical potentials of reservoirs are identical.
The Markovian time evolution of the entropy production rate is studied as a measure of irreversibility generated in a bipartite quantum system consisting of two coupled bosonic modes immersed in a common thermal environment. The dynamics of the system is described in the framework of the formalism of the theory of open quantum systems based on completely positive quantum dynamical semigroups, for initial two-mode squeezed thermal states, squeezed vacuum states, thermal states and coherent states. We show that the rate of the entropy production of the initial state and nonequilibrium stationary state, and the time evolution of the rate of entropy production, strongly depend on the parameters of the initial Gaussian state (squeezing parameter and average thermal photon numbers), frequencies of modes, parameters characterising the thermal environment (temperature and dissipation coefficient), and the strength of coupling between the two modes. We also provide a comparison of the behaviour of entropy production rate and Rényi-2 mutual information present in the considered system.
This paper deals with some thermodynamical aspects of a class of models in non equilibrium quantum statistical mechanics (QSM) which are commonly used to describe the behaviour of infinite quantum systems perturbed by a time‐dependent periodic force. We are interested to the thermodynamical properties of the set of non‐equilibrium steady states (NESS) of the perturbed system. We extend the construction of the C‐Liouvillean originally introduce in [1] to our time‐dependent situation to define the C‐Liouvillean of Floquet KF. The NESS are thus described by zero‐resonance eigenvectors of KF*. We also give a time dependent version of the rate of entropy production [2] for the perturbed system based on the relative entropy as defined by Araki [3] in terms of the relative modular operator.
We investigate the link between the irreversibility generated by a stationary dissipative process and the correlations established within a composite quantum system. We provide two equivalent expressions for the entropy generated in the non-equilibrium steady state of coupled quantum harmonic oscillators that allow for a simple interpretation of the onset of irreversibility. We then unveil a quantitative relation between the entropy production rate and correlations, both total and quantum, built between the two oscillators. In the small-coupling limit, the entropy production rate is shown to be proportional to both the mutual information and the quantum correlations. We apply our results to the analysis of the optomechanical interaction between a nano-mechanical resonator and a cavity field, and show that the behavior of the entropy production captures the peculiar features of the model, such as sideband cooling and amplification.
Abstract This paper investigates the dynamics of current and quantum transport factor in a bosonic system consisting of a central system interacting with two reservoirs at different temperatures. We derive a master equation describing the time evolution of the density matrix of the system, accounting for the interactions and energy transfer between the components. We quantify the current, representing the flow of bosons through the system and analyse its dependence on the system's parameters and temperatures of the thermal reservoirs. In the steady state regime, we derived an expression for the quantum transport factor of the energy transfer process. Our analysis show that quantum effects, such as the dependence on temperature can significantly impact this factor. In particular, we observe that the transport factor of the quantum system is greater than the corresponding factor when the temperature goes to infinity, where the factor has an identical form with the Carnot efficiency of an ideal heat engine. We then derived the Fokker-Planck equation to find out the Glauber-Sudarsan P-representation. In the steady state of the equation, the probability distribution comes out to be in Gaussian form. We then calculated the entropic force for this probability distribution which gives the Hooke's law in the steady state, in agreement with the fact that our system is a harmonic oscillator.
The present thesis is concerned with the study of a quantum physical system composed of a small particle system (such as a spin chain) and several quantized massless boson fields (as photon gasses or phonon fields) at positive temperature. The setup serves as a simplified model for matter in interaction with thermal "radiation" from different sources. Hereby, questions concerning the dynamical and thermodynamic properties of particle-boson configurations far from thermal equilibrium are in the center of interest. We study a specific situation where the particle system is brought in contact with the boson systems (occasionally referred to as heat reservoirs) where the reservoirs are prepared close to thermal equilibrium states, each at a different temperature. We analyze the interacting time evolution of such an initial configuration and we show thermal relaxation of the system into a stationary state, i.e., we prove the existence of a time invariant state which is the unique limit state of the considered initial configurations evolving in time. As long as the reservoirs have been prepared at different temperatures, this stationary state features thermodynamic characteristics as stationary energy fluxes and a positive entropy production rate which distinguishes it from being a thermal equilibrium at any temperature. Therefore, we refer to it as non-equilibrium stationary state or simply NESS. The physical setup is phrased mathematically in the language of C*-algebras. The thesis gives an extended review of the application of operator algebraic theories to quantum statistical mechanics and introduces in detail the mathematical objects to describe matter in interaction with radiation. The C*-theory is adapted to the concrete setup. The algebraic description of the system is lifted into a Hilbert space framework. The appropriate Hilbert space representation is given by a bosonic Fock space over a suitable L2-space. The first part of the present work is concluded by the derivation of a spectral theory which connects the dynamical and thermodynamic features with spectral properties of a suitable generator, say K, of the time evolution in this Hilbert space setting. That way, the question about thermal relaxation becomes a spectral problem. The operator K is of Pauli-Fierz type. The spectral analysis of the generator K follows. This task is the core part of the work and it employs various kinds of functional analytic techniques. The operator K results from a perturbation of an operator L0 which describes the non-interacting particle-boson system. All spectral considerations are done in a perturbative regime, i.e., we assume that the strength of the coupling is sufficiently small. The extraction of dynamical features of the system from properties of K requires, in particular, the knowledge about the spectrum of K in the nearest vicinity of eigenvalues of the unperturbed operator L0. Since convergent Neumann series expansions only qualify to study the perturbed spectrum in the neighborhood of the unperturbed one on a scale of order of the coupling strength we need to apply a more refined tool, the Feshbach map. This technique allows the analysis of the spectrum on a smaller scale by transferring the analysis to a spectral subspace. The need of spectral information on arbitrary scales requires an iteration of the Feshbach map. This procedure leads to an operator-theoretic renormalization group. The reader is introduced to the Feshbach technique and the renormalization procedure based on it is discussed in full detail. Further, it is explained how the spectral information is extracted from the renormalization group flow. The present dissertation is an extension of two kinds of a recent research contribution by Jakšić and Pillet to a similar physical setup. Firstly, we consider the more delicate situation of bosonic heat reservoirs instead of fermionic ones, and secondly, the system can be studied uniformly for small reservoir temperatures. The adaption of the Feshbach map-based renormalization procedure by Bach, Chen, Fröhlich, and Sigal to concrete spectral problems in quantum statistical mechanics is a further novelty of this work.