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11.
We study decoherence in a simple quantum mechanical model using two approaches. Firstly, we follow the conventional approach to decoherence where one is interested in solving the reduced density matrix from the perturbative master equation. Secondly, we consider our novel correlator approach to decoherence where entropy is generated by neglecting observationally inaccessible correlators. We show that both methods can accurately predict decoherence time scales. However, the perturbative master equation generically suffers from instabilities which prevents us to reliably calculate the system’s total entropy increase. We also discuss the relevance of the results in our quantum mechanical model for interacting field theories. 相似文献
12.
We investigate the effects of three-site interactions on the pairwise entanglement in a three-qubit Heisenberg XX model. We find the three-site interactions only in favor of the thermal entanglement and benefit the teleportation between the next-to-nearest neighbor qubits. In addition, we also study the stationary entangled state in the model with intrinsic decoherence taken into account. The influence of different types of three-site interactions on the stationary entangled state is then examined. 相似文献
13.
We present a detailed account of the technical aspects of stochastic quantum molecular dynamics, an approach introduced recently by the authors [H. Appel, M. Di Ventra, Phys. Rev. B 80 (2009) 212303] to describe coupled electron-ion dynamics in open quantum systems. As example applications of the method we consider both finite systems with and without ionic motion, as well as describe its applicability to extended systems in the limit of classical ions. The latter formulation allows the study of important phenomena such as decoherence and energy relaxation in bulk systems and surfaces in the presence of time-dependent fields. 相似文献
14.
Kamil Walczak 《Central European Journal of Physics》2006,4(2):241-253
In this work we study the effect of decoherence on elastic and polaronic transport via discrete quantum states. Calculations
are performed with the help of a nonperturbative computational scheme, based on Green’s function theory within the framework
of polaron transformation (GFT-PT), where the many-body electron-phonon interaction problem is mapped exactly into a single-electron
multi-channel scattering problem. In particular, the influence of dephasing and relaxation processes on the shape of the electrical
current and shot noise curves is discussed in detail under linear and nonlinear transport conditions. 相似文献
15.
能级间同时存在衰变和跃迁时的消相干特性 总被引:4,自引:0,他引:4
二能级原子在量子信息中可视为量子位.本文基于约化密度矩阵理论,利用量子纯态和混合态分析方法,针对二能级原子能级间同时存在衰变和跃迁的情况,研究原子消相干特性. 相似文献
16.
Vinay Ambegaokar 《Journal of statistical physics》2006,125(5-6):1183-1192
The time development of the reduced density matrix for a quantum oscillator damped by coupling it to an ohmic environment
is calculated via an identity of the Debye-Waller form. Results obtained some years ago by Hakim and the author in the free-particle
limit(10) are thus recovered. The evolution of a free particle in a prepared initial state is examined, and a previously published
exchange(5,9) is illuminated with figures showing no decoherence without dissipation.
PACS number: 03.75.Ss 相似文献
17.
G. Benenti S. Felloni G. Strini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):389-396
We study the stability under quantum noise effects of the quantum privacy amplification protocol for the purification of entanglement
in quantum cryptography. We assume that the E91 protocol is used by two communicating parties (Alice and Bob) and that the
eavesdropper Eve uses the isotropic Bužek-Hillery quantum copying machine to extract information.
Entanglement purification is then operated by Alice and Bob by means of the quantum privacy amplification protocol and we
present a systematic numerical study of the impact of all possible
single-qubit noise channels on this protocol. We find that both the qualitative behavior of the fidelity of the purified state
as a function of the number of purification steps and
the maximum level of noise that can be tolerated by the protocol strongly depend on the specific noise channel. These results
provide valuable information for experimental implementations of the quantum privacy amplification protocol. 相似文献
18.
The properties of some complex many body systems can be modeled by introducing in the dissipative dynamics of each single component a set of kinetic constraints that depend on the state of the neighbor systems. Here, we characterize this kind of dynamics for two quantum systems whose independent dissipative evolutions are defined by a Lindblad equation. The constraints are introduced through a set of projectors that restrict the action of each single dissipative Lindblad channel to the state of the other system. Conditions that guarantee a classical interpretation of the kinetic constraints are found. The generation and evolution of entanglement is studied for two optical qubits systems. Classically constrained dissipation leads to a stationary state whose degree of entanglement depends on the initial state. Nevertheless, independently of the initial conditions, a maximal entangled state is generated when both systems are subjected to the action of local Hamiltonian fields that do not commutate with the constraints. The underlying physical mechanism is analyzed in detail. 相似文献
19.
The effect of anisotropy for fluctuations of electric currents in magnetic field is addressed within framework of quantum measurements theory. It is shown that for free fermions in uniform magnetic field the anisotropy is of the same sign as one expects for chiral magnetic effect and is related to triangle anomaly. The corresponding decoherence functional contains anomalous off-diagonal terms leading to correlation of fluctuations between observables of opposite P-parity. 相似文献
20.
The phonon induced mechanisms of relaxation/decoherence in quantum dots are analysed. A non-perturbative technique - a modification of the Davydov transformation appropriate to the localised particles is applied for solving the electron-phonon eigenvalue problem in a quantum dot at magnetic field presence. The decay rates for polaron relaxation via the anharmonicity induced channel are analysed in details. In particular, it is indicated that previous, of perturbative type, estimations of the anharminicity induced relaxation rates were too severe and after including the coherence effects they are of, at least, one order longer. The process of exciton dressing with phonons is also analysed as the unavoidable source of picosecond scale decoherence in optically driven nanostructures. A break-down of an instant Pauli spin blocking mechanism and a large enhancement of the Fröhlich constant for confined electrons are also addressed. 相似文献