Decoherence in Open Quantum Systems (original) (raw)
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Quantum decoherence in the theory of open systems
2007
In the framework of the Lindblad theory for open quantum systems, we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. It is found that the system manifests a quantum decoherence which is more and more significant in time. We calculate also the decoherence time scale and analyze the transition from quantum to classical behaviour of the considered system.
Quantum decoherence of the damped harmonic oscillator
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In the framework of the Lindblad theory for open quantum systems, we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. It is found that the system manifests a quantum decoherence which is more and more significant in time. We also calculate the decoherence time and show that it has the same scale as the time after which thermal fluctuations become comparable with quantum fluctuations.
Decoherence in quantum open systems revisited
2002
The following statements belonging to the folklore of the theory of environmental decoherence are shown to be incorrect: 1) linear coupling to harmonic oscillator bath is a universal model of decoherence, 2) chaotic environments are more efficient decoherers.
Fortschritte der Physik, 1999
In the framework of the Lindblad theory for open quantum systems, expressions for the density operator, von Neumann entropy and effective temperature of the damped harmonic oscillator are obtained. The entropy for a state characterized by a Wigner distribution function which is Gaussian in form is found to depend only on the variance of the distribution function. We give a series of inequalities, relating uncertainty to von Neumann entropy and linear entropy. We analyze the conditions for purity of states and show that for a special choice of the diffusion coefficients, the correlated coherent states (squeezed coherent states) are the only states which remain pure all the time during the evolution of the considered system. These states are also the most stable under evolution in the presence of the environment and play an important role in the description of environment induced decoherence.
Decoherence in composite quantum open systems: the effectiveness of unstable degrees of freedom
The effect induced by an environment on a composite quantum system is studied. The model considers the composite system as comprised by a subsystem A coupled to a subsystem B which is also coupled to an external environment. We study all possible four combinations of subsystems A and B made up with a harmonic oscillator and an upside down oscillator. We analyzed the decoherence suffered by subsystem A due to an effective environment composed by subsystem B and the external reservoir. In all the cases we found that subsystem A decoheres even though it interacts with the environment only through its sole coupling to B. However, the effectiveness of the diffusion depends on the unstable nature of subsystem A and B. Therefore, the role of this degree of freedom in the effective environment is analyzed in detail.
Quantum Decoherence at Finite Temperatures
We study measures of decoherence and thermalization of a quantum system S in the presence of a quantum environment (bath) E. The whole system is prepared in a canonical thermal state at a finite temperature. Applying perturbation theory with respect to the system-environment coupling strength, we find that under common Hamiltonian symmetries, up to first order in the coupling strength it is sufficient to consider the uncoupled system to predict decoherence and thermalization measures of S. This decoupling allows closed form expressions for perturbative expansions for the measures of decoherence and thermalization in terms of the free energies of S and of E. Numerical results for both coupled and decoupled systems with up to 40 quantum spins validate these findings.
Decoherence of an Open System under Continuous Quantum Measurement of Energy
International Journal of Theoretical Physics, 2009
We study continuous quantum measurements (CQM) of energy of an open quantum system by Lindblad master equation. It turns out that the time-dependence of decoherence is identified. We conclude that the CQM of energy accelerate quantum decoherence. Keywords Continuous quantum measurements • Decoherence • Master equation • Density matrix elements The simplest description of a measurement in quantum physics was provided by von Neumann [1]. When quantum measurement was first introduced to quantum mechanics, it was invariably treated by ignoring the time the measurement takes. However, it is not sufficient to describe continuously monitored system. Usually, one wants to understand what happens to the system while the measurement takes place continuously. This is the subject of continuous quantum measurement [2]. Recently, continuous or repeated measurements of quantum system has been actively discussed due to its implication in feedback control [3], metrology [4-7], quantum information [8], quantum computing [9-11] and its importance in understanding the quantum to classical transition [12-15]. When a quantum system is measured, its state is changed which may be described as decoherence. Decoherence is a basic idea in the theory of CQM which plays a decisive role in the dynamics of a system subject to repeated or continuous quantum measurement. The interest in decoherence is widespread, due to the fact that it is the main limiting factor for quantum information processing [16]. Sponsored by K.C. Wong Magna Fund in Ningbo University.
Decoherence and thermalization dynamics of a quantum oscillator
Journal of Optics B: Quantum and Semiclassical Optics, 2000
We introduce the quantitative measures characterizing the rates of decoherence and thermalization of quantum systems. We study the time evolution of these measures in the case of a quantum harmonic oscillator whose relaxation is described in the framework of the standard master equation, for various initial states (coherent, 'cat', squeezed and number). We establish the conditions under which the true decoherence measure can be approximated by the linear entropy 1 − Trρ 2. We show that at low temperatures and for highly excited initial states the decoherence process consists of three distinct stages with quite different time scales. In particular, the 'cat' states preserve 50% of the initial coherence for a long time interval which increases logarithmically with increase of the initial energy.
Decoherence and asymptotic entanglement in open quantum dynamics
Journal of Russian Laser Research, 2007
Within the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we determine the degree of quantum decoherence of a harmonic oscillator interacting with a thermal bath. It is found that the system manifests a quantum decoherence which is more and more significant in time. We also calculate the decoherence time and show that it has the same scale as the time after which thermal fluctuations become comparable with quantum fluctuations. We solve the master equation for two independent harmonic oscillators interacting with an environment in the asymptotic long-time regime. We give a description of the continuous-variable asymptotic entanglement in terms of the covariance matrix of quantum states of the considered system for an arbitrary Gaussian input state. Using the Peres-Simon necessary and sufficient condition for separability of two-mode Gaussian states, we show that the two noninteracting systems immersed in a common environment become asymptotically entangled for certain environments, so that in the long-time regime they manifest nonlocal quantum correlations.
Pure Decoherence in Quantum Systems
Open Systems & Information Dynamics, 2004
A popular model of decoherence based on the linear coupling to harmonic oscillator heat baths is analysed and shown to be inappropriate in the regime where decoherence dominates over energy dissipation, called pure decoherence regime. The similar mechanism essentially related to the energy conservation implies that, on the contrary to some recent conjectures [21], chaotic environments can be less efficient decoherers than regular ones. Finally, the elastic scattering mechanism is advocated as the simplest source of pure decoherence.