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arXiv:0905.1107 · Journal of Physics A Mathematical and Theoretical

Temperature effects on a network of dissipative quantum harmonic oscillators: collective damping and dispersion processes

M. A. de Ponte, Salomon Sylvain Mizrahi, M. H. Y. Moussa

Published Aug 24, 2009• 10 citations
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Abstract

In this article we extend the results presented in Ref. [Phys. Rev. A 76, 032101 (2007)] to treat quantitatively the effects of reservoirs at finite temperature in a bosonic dissipative network: a chain of coupled harmonic oscillators whichever its topology, i.e., whichever the way the oscillators are coupled together, the strength of their couplings and their natural frequencies. Starting with the case where distinct reservoirs are considered, each one coupled to a corresponding oscillator, we also analyze the case where a common reservoir is assigned to the whole network. Master equations are derived for both situations and both regimes of weak and strong coupling strengths between the network oscillators. Solutions of these master equations are presented through the normal ordered characteristic function. We also present a technique to estimate the decoherence time of network states by computing separately the effects of diffusion and the attenuation of the interference terms of the Wigner function. A detailed analysis of the diffusion mechanism is also presented through the evolution of the Wigner function. The interesting collective diffusion effects are discussed and applied to the analysis of decoherence of a class of network states. Finally, the entropy and the entanglement of a pure bipartite system are discussed.

DOI
10.1088/1751-8113/42/36/365304

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In this article we extend the results presented in Ref. [Phys. Rev. A 76, 032101 (2007)] to treat quantitatively the effects of reservoirs at finite temperature in a bosonic dissipative network: a chain of coupled harmonic oscillators whichever its topology, i.e., whichever the way the oscillators are coupled together, the strength of their couplings and their natural frequencies. Starting with the case where distinct reservoirs are considered, each one coupled to a corresponding oscillator, we also analyze the case where a common reservoir is assigned to the whole network. Master equations are derived for both situations and both regimes of weak and strong coupling strengths between the network oscillators. Solutions of these master equations are presented through the normal ordered characteristic function. We also present a technique to estimate the decoherence time of network states by computing separately the effects of diffusion and the attenuation of the interference terms of the Wigner function. A detailed analysis of the diffusion mechanism is also presented through the evolution of the Wigner function. The interesting collective diffusion effects are discussed and applied to the analysis of decoherence of a class of network states. Finally, the entropy and the entanglement of a pure bipartite system are discussed.
We present a general treatment of a bosonic dissipative network: a chain of coupled dissipative harmonic oscillators whatever its topology---i.e., whichever the way the oscillators are coupled together, the strength of their couplings, and their natural frequencies. Starting with a general more realistic scenario where each oscillator is coupled to its own reservoir, we also discuss the case where all the network oscillators are coupled to a common reservoir. We obtain the master equation governing the dynamic of the network states and the associated evolution equation of the Glauber-Sudarshan PPP function. With these instruments we briefly show how to analyze the decoherence and the evolution of the linear entropy of general states of the network. We also show how to obtain the master equation for the case of distinct reservoirs from that of a common one.
We analyze the behavior of a damped quantum harmonic oscillator immersed in a heat bath with a nonlinear coupling. For this purpose, we construct a generalized master equation (GME) for the reduced density of the oscillator. We specialize the results for a quadratic coupling in the presence of a bosonic reservoir and an Ohmic dissipation model, analyzing the evolution equation for the mean value of the oscillator coordinate. In the asymptotic case we obtain a gain-loss master equation whose transition rates are polynomials in the number of quanta. No explicit solutions other than the equilibrium one can be written, since the standard methods do not apply. The equilibrium solution is investigated and the eigenvalues of the corresponding spectral problem are numerically computed to study the effect of the nonlinearity on the evolution of the system. By means of the Wigner transformation of the GME, we extract a third-order partial derivative equation that represents the semiclassical evolution of the damped oscillator. In the classical limit this is a nonlinear Fokker-Planck equation.
In this work we analyze the coherence dynamics and estimate decoherence times of quantum states in a network where a central dissipative oscillator is coupled with $N\ensuremath{-}1$ peripheral noninteracting dissipative oscillators. The results obtained here are compared with those in part I of this work where a symmetric network was considered. This comparison helps us to understand the influence of the topology of a network on the coherence dynamics of quantum superposition states. As in part I, master equations are derived for regimes of both weak and strong coupling between the oscillators. Decoherence times of particular states of the network are computed and the results are analyzed in the light of state swap and recurrence processes of reduced states of the network. The linear entropies of the joint and reduced systems are also analyzed.
In this work we analyze the coherence dynamics and estimate decoherence times of quantum states in a network composed of NNN coupled dissipative quantum oscillators. We assume a symmetric network where all oscillators are coupled to each other with the same coupling strength. Master equations are derived for regimes of both weak and strong coupling between the oscillators. The strong coupling regime is characterized by the coupling strength between the oscillators or by the number of oscillators in the network. The decoherence times of particular states of the network are computed and the results are clarified by analyzing the processes of state swap and recurrence of reduced states of the network together with the linear entropies of the joint and reduced systems.
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We study the quantum dynamics of an open network of two-level systems which is coupled to a correlated common environment represented by a bosonic field in a thermal equilibrium state. Extensive numerical simulations of the full second-order time-convolutionless quantum master equation for the density matrix of various types of networks are performed, in order to investigate dissipation and decoherence processes and, in particular, their dependence on the spatial separation of the network sites and on the speed of the bosonic field modes. In the limit of an infinite speed the influence of the environment disappears due to the emergence of a decoherence-free subspace, while the limit of zero speed corresponds to the case in which the network sites are coupled to independent reservoirs, a case which is much easier to treat numerically. The main result of the paper is a general intuitive criterion which states that the simpler model of independent reservoirs can be used as long as the network relaxation time is smaller than the time it takes for the modes to travel the minimal distance between the network sites.