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Mozyrsky, Dmitry; Privman, Vladimir

doi:10.1023/a:1023042014131

Cited by 82 publications

(166 citation statements)

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“…This time dependence can involve an oscillatory behavior corresponding to the initial regime of approximately coherent evolution, with frequencies de- * Electronic address: tolkunov@clarkson.edu † Electronic address: privman@clarkson.edu ‡ Electronic address: paravind@wpi.edu termined by the energy gaps of the system (which can be shifted by the noise). At the same time, there will be irreversible, decay-type time dependencies manifest for larger time scales, which can in many cases be identified with processes such as relaxation, thermalization, pure decoherence, etc., that represent irreversible noiseinduced behaviors [7,8,9,10,11,12,13,14,15,16].One, by no means unique, way to quantify the degree of loss of coherence is by the decay of the absolute values of off-diagonal elements of the reduced density matrix. This definition is only meaningful at relatively late stages of the dynamics, when the density matrix has already become nearly diagonal in a basis favored by external and internal interactions, and by environmental influences, e.g., for thermalization, the energy basis.…”

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Decoherence of a measure of entanglement

2005

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We demonstrate by an explicit model calculation that the decay of entanglement of two two-state systems (two qubits) is governed by the product of the factors that measure the degree of decoherence of each of the qubits, subject to independent sources of quantum noise. This demonstrates an important physical property that separated open quantum systems can evolve quantum mechanically on time scales larger than the times for which they remain entangled. Entanglement of quantum-mechanical states, referring to the nonlocal quantum correlations between subsystems, is one of the key resources in the field of quantum information science. Many protocols in quantum communication and quantum computation are based on entangled states [1]. When one considers practical applications of entanglement, the coupling of the quantum system and its subsystems to the environment, resulting in decoherence, should be taken into account. It is known [2,3] that entanglement cannot be restored by local operations and classical communications once it has been lost, so understanding of the dynamics of decoherence of entanglement is of importance in many applications.There are two basic issues in the physics of the loss of entanglement by decoherence, that, while intuitively suggestive, thus far have allowed little quantitative, modelbased understanding. To define them, let us refer to two subsystems, S (1) and S (2) , of the combined system, S. The first property of interest is the expectation that when the systems are separated in that they are subject to independent sources of noise, e.g., when they are spatially far apart, then the decoherence of entanglement is faster [4,5,6] than the loss of coherence in the quantummechanical behavior of each of the subsystems. Thus, the subsystems can for some time still behave approximately in a coherent quantum-mechanical manner, but without correlation with each other.In order to define the second property of interest, let us point out that the definition of "decoherence" of an open quantum system is not unique. One has to consider the overall time-dependent behavior of the reduced density matrix of the system, obtained for a model of the environmental modes, which are the source of noise and are traced over. This time dependence can involve an oscillatory behavior corresponding to the initial regime of approximately coherent evolution, with frequencies de- * Electronic address: tolkunov@clarkson.edu † Electronic address: privman@clarkson.edu ‡ Electronic address: paravind@wpi.edu termined by the energy gaps of the system (which can be shifted by the noise). At the same time, there will be irreversible, decay-type time dependencies manifest for larger time scales, which can in many cases be identified with processes such as relaxation, thermalization, pure decoherence, etc., that represent irreversible noiseinduced behaviors [7,8,9,10,11,12,13,14,15,16].One, by no means unique, way to quantify the degree of loss of coherence is by the decay of the absolute values of off-diagonal elements of the re...

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“…Each spin interacts with a bosonic bath of modes H r B = k ω r k b r † k b r k , which has been widely used [8,12,14] as a model of quantum noise (we set = 1). The interaction between the quantum systems and the environment is taken in the form…”

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Decoherence of a measure of entanglement

2005

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“…(61) is, apart a factor 2, equal to that of the vacuum contribution to the decoherence function (20). This result appears to give a strong indication that it is just the buildup of correlations among the various momenta that compose the wave packet and the corresponding associated transverse photons that leads to vacuum decoherence in our system.…”

Section: A Field Structure Dynamicsmentioning

confidence: 65%

“…Now, we calculate the average of the operatorâ † k,jâ k,j using the trace in the coherent states basis, that for a generic operatorÂ has the form [20] TrÂ…”

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Loss of coherence and dressing in QED

Bellomo

Petruccione

2006

Phys. Rev. A

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The dynamics of a free charged particle, initially described by a coherent wave packet, interacting with an environment, i.e. the electromagnetic field characterized by a temperature T , is studied. Using the dipole approximation the exact expressions for the evolution of the reduced density matrix both in momentum and configuration space and the vacuum and the thermal contribution to decoherence, are obtained. The time behaviour of the coherence lengths in the two representations are given. Through the analysis of the dynamic of the field structure associated to the particle the vacuum contribution is shown to be linked to the birth of correlations between the single momentum components of the particle wave packet and the virtual photons of the dressing cloud.

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Dynamic Decoupling Quantum Control Methods

Cong

2014

Control of Quantum Systems

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Since the birth of quantum mechanics in the twentieth century, it has achieved great success in many ways as a fundamental theory of natural sciences. With the development of science, the combination of quantum mechanics, classical information theory, and computing technology led to the emergence of quantum information theory and quantum theory of computation. A series of topics based on quantum information technology have been proposed, and the realization of quantum computers (Feynman, 1982) is one of the important research areas. Coherence and entanglement are essential for quantum computation and quantum information processing, but decoherence destroys the coherence of the quantum superposition states in the process of evolution and results in the reduction or even the erosion of the entanglement between subsystems. In order to maintain quantum coherence, quantum error-correcting codes a dynamic coupling scheme (Viola and Lloyd, 1998) (originally known as quantum bang-bang (BB) control) were proposed. Quantum error-correcting codes and quantum error-avoiding codes need to introduce a lot of redundant information, and also add a certain symmetry assumptions between the system and the environment. Compared with these two methods, BB control does not require the introduction of redundant qubits. The BB control scheme makes use of coherent averaging effects (Haeberlen and Waugh, 1968) and uses twin-born tailored powerful pulses to average out the effect of the unwanted Hamiltonian. After the quantum dynamical decoupling scheme was proposed by Viola and Lloyd in 1998, it was used to suppress the decoherence for one qubit. In recent years, the BB control schemes for phase decoherence in thê-, V-, and Ξ-configurations in three-level atoms have been studied (Liu et al., 2005a,b), and the BB control scheme for amplitude decoherence was designed by Cao, Liu, and Bai (2008). The BB control scheme to suppress phase decoherence in a four-level atom system in the Ξ-configuration is discussed in

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Cited by 82 publications

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Decoherence of a measure of entanglement

Decoherence of a measure of entanglement

Loss of coherence and dressing in QED

Dynamic Decoupling Quantum Control Methods

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