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Zhongguo kexue. Wulixue Lixue Tianwenxue

Adiabatic manipulation and decoherence dynamics of quantum correlations

Min Li, Wanfang Liu, Zheng Li

Published May 17, 2019• 0 citations
Publisher

Abstract

By adiabatically manipulating the Rabi frequency of the drive field, the quantum discord (QD) has been used to analyze the quantum correlation for two atoms of the ensemble under the electromagnetically induced transparency (EIT) mechanism. It is shown that, the quantum correlation of two atoms depends on the Rabi frequency of the drive field, the excitation mode, the photon number and the atom number of the ensemble. If more than half of atoms were excited, the ensemble can generate the maximum quantum correlation. Furthermore, we investigate the behavior of the quantum correlation under three decoherence channels respectively. It is found that the sudden death of the quantum correlation do not exist in any decoherence channel. Generated via the full excitation mode with a small mixed angle, the quantum correlation has a strong survival ability under the amplitude damping channel, but for a larger mixed angle, the survival ability is stronger under phase damping channel. The quantum correlation generated via the half excitation mode displays a strong survive ability for arbitrary mixed angle under the amplitude damping channel. By manipulating the Rabi frequency in this excitation mode, for an appropriate mixed angel, survivability of quantum correlation reverses under the phase damping channel and the depolarizing channel. But when the mixed angle reaches the critical value towards π/2 with the number of atoms increasing. For the low excitation mode with any mixed angle, the quantum correlation survives more easily under the amplitude damping channel, conversely, it survives more difficultly under the depolarizing channel.

DOI
10.1360/sspma2018-00326

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By adiabatically manipulating the Rabi frequency of the drive field, the quantum discord (QD) has been used to analyze the quantum correlation for two atoms of the ensemble under the electromagnetically induced transparency (EIT) mechanism. It is shown that, the quantum correlation of two atoms depends on the Rabi frequency of the drive field, the excitation mode, the photon number and the atom number of the ensemble. If more than half of atoms were excited, the ensemble can generate the maximum quantum correlation. Furthermore, we investigate the behavior of the quantum correlation under three decoherence channels respectively. It is found that the sudden death of the quantum correlation do not exist in any decoherence channel. Generated via the full excitation mode with a small mixed angle, the quantum correlation has a strong survival ability under the amplitude damping channel, but for a larger mixed angle, the survival ability is stronger under phase damping channel. The quantum correlation generated via the half excitation mode displays a strong survive ability for arbitrary mixed angle under the amplitude damping channel. By manipulating the Rabi frequency in this excitation mode, for an appropriate mixed angel, survivability of quantum correlation reverses under the phase damping channel and the depolarizing channel. But when the mixed angle reaches the critical value towards π/2 with the number of atoms increasing. For the low excitation mode with any mixed angle, the quantum correlation survives more easily under the amplitude damping channel, conversely, it survives more difficultly under the depolarizing channel.
We study the multipartite correlations of the multiatom dark states, which are characterized by the atomic squeezing beyond the pairwise entanglement. It is shown that, in the photon storage process with atomic ensemble via the electromagnetically induced transparency (EIT) mechanism, the atomic squeezing and the pairwise entanglement can be created by adiabatically manipulating the Rabi frequency of the classical light field on the atomic ensemble. We also consider the sudden death for the atomic squeezing and the pairwise entanglement under various decoherence channels. An optimal time for generating the greatest atomic squeezing and pairwise entanglement is obtained by studying in detail the competition between the adiabatic creation of quantum correlation in the atomic ensemble and the decoherence that we describe with three typical decoherence channels.
We calculate the dissipative dynamics of two-qubit quantum discord under Markovian environments. We analyze various dissipative channels such as dephasing, depolarizing, and generalized amplitude damping, assuming independent perturbation, in which each qubit is coupled to its own channel. Choosing initial conditions that manifest the so-called sudden death of entanglement, we compare the dynamics of entanglement with that of quantum discord. We show that in all cases where entanglement suddenly disappears, quantum discord vanishes only in the asymptotic limit, behaving similarly to individual decoherence of the qubits, even at finite temperatures. Hence, quantum discord is more robust than the entanglement against decoherence so that quantum algorithms based only on quantum discord correlations may be more robust than those based on entanglement.
We study the dynamics of quantum dissension for three qubit states in various dissipative channels such as amplitude damping, dephasing and depolarizing. Our study is solely based on Markovian environments where quantum channels are without memory and each qubit is coupled to its own environment. We start with mixed GHZ, mixed W, mixture of separable states, a mixed biseparable state, as the initial states and mostly observe that the decay of quantum dissension is asymptotic in contrast to sudden death of quantum entanglement in similar environments. This is a clear indication of the fact that quantum correlation in general is more robust against the effect of noise. However, for a given class of initial mixed states we find a temporary leap in quantum dissension for a certain interval of time. More precisely, we observe the revival of quantum correlation to happen for certain time period. This signifies that the measure of quantum correlation such as quantum discord, quantum dissension, defined from the information theoretic perspective is different from the correlation defined from the entanglement-separability paradigm and can increase under the effect of the local noise. We also study the effects of these channels on the monogamy score of each of these initial states. Interestingly, we find that for certain class of states and channels, there is change from negative values to positive values of the monogamy score with classical randomness as well as with time. This gives us an important insight in obtaining states which are freely sharable (polygamous state) from the states which are not freely sharable (monogamous). This is indeed a remarkable feature, as we can create monogamous states from polygamous states Monogamous states are considered to have more signatures of quantum ness and can be used for security purpose.
Quantum correlations between two or more different degrees of freedom of the same particle is sometimes referred to as intraparticle entanglement. In this work, we study these intra-particle correlations between two different degrees of freedom under various decoherence channels viz. amplitude damping, depolarising and phase damping channels. We observe a unique feature of the amplitude damping channel, wherein entanglement is shown to arise starting from separable states. In case of non maximally entangled input states, in addition to entanglement sudden death, the creation of entanglement is also observed, having an asymptotic decay over a long time. These counter-intuitive behaviours arise due to the subtle interplay of channel and input state parameters, and are not seen for interparticle entanglement without consideration of non-Markovian noise. It is also not observed for maximally entangled input states. Furthermore, investigation of entanglement evolution in phase damping and depolarizing channels shows its robustness against decoherence as compared to interparticle entanglement.
Abstract Quantum discord, an appropriate measure of quantum correlation, is analyzed in a two-mode Gaussian state of the cavity field evolved by a system of quantum beat laser. In the laser system, two arbitrary single-mode Gaussian states of the cavity fields and an external classical field couple to the atomic lasing medium. We calculate the time-dependent expression for the quantum discord both analytically and numerically, by following the reduced density matrix equation of the resulting cavity field. In this framework, we investigate the generation and control of Gaussian quantum discord in the two-mode Gaussian state of the cavity field at the output in terms of the purity and non-classicality of the two input cavity modes, the Rabi frequency of the classical driving field, the relative phase of the coupling parameters, and the damping rates of the cavity modes. The behaviour of quantum discord appears oscillatory due to the quantum beats in the output cavity field developed by the classical driving field in the medium as time passes. Moreover, we find that quantum discord switches on and off while adjusting the relative phase of the coupling parameters. Analysis of the analytical results agrees well with our numerical simulations.
In this paper, we investigate the quantum correlation of coupled qubits which are initially in maximally entangled mixed states in a squeezed vacuum reservoir. We compare and analyze the effects of squeezed parameters on quantum discord and quantum concurrence. The results show that in a squeezed vacuum reservoir, the quantum discord and quantum concurrence perform with completely opposite behaviors with the change of squeezed parameters. Quantum discord survives longer with the increase of squeezed amplitude parameter, but entanglement death is faster on the contrary. The results also indicate that the classical correlation of the system is smaller than quantum discord in a vacuum reservoir, while it is bigger than quantum discord in a squeezed vacuum reservoir. The quantum discord and classical correlation are more robust than quantum concurrence in the two reservoir environments, which indicates that the entanglement actually is easily affected by decoherence and quantum discord has a stronger ability to avoid decoherence in a squeezed vacuum reservoir.