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Journal of the Physical Society of Japan

Dynamics of Quantum Correlation in de Sitter Spacetime

Zhiming Huang, Zehua Tian

Published Aug 28, 2017• 9 citations
Publisher

Abstract

In this article, we investigate the dynamics of quantum correlation for two atoms interacting with massless scalar field in the background of de Sitter spacetime. We firstly derive the solving process of master equation that governs the system evolution with initial Werner state. Then we discuss the production, revival and decay of quantum correlation for three cases of different initial states: zero-correlation state, non zero-correlation separable state and maximally entangled state. We find that quantum correlation degrades as temperature and the two-atom distance increase. Compared with the sudden death and birth of entanglement, quantum correlation change more smoothly and thus is more robust to decoherence, which can remain stable for long time when two atoms are very close.

DOI
10.7566/jpsj.86.094003

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In this article, we investigate the dynamics of quantum correlation for two atoms interacting with massless scalar field in the background of de Sitter spacetime. We firstly derive the solving process of master equation that governs the system evolution with initial Werner state. Then we discuss the production, revival and decay of quantum correlation for three cases of different initial states: zero-correlation state, non zero-correlation separable state and maximally entangled state. We find that quantum correlation degrades as temperature and the two-atom distance increase. Compared with the sudden death and birth of entanglement, quantum correlation change more smoothly and thus is more robust to decoherence, which can remain stable for long time when two atoms are very close.
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We investigate the radiative processes of a quantum system composed by two identical two-level atoms in the de Sitter spacetime, interacting with a conformally coupled massless scalar field prepared in the de Sitter-invariant vacuum. We discuss the structure of the rate of variations of the atomic energy for two static atoms. Following a procedure developed by Dalibard, Dupont-Roc, and Cohen-Tannoudji, our intention is to identify in a quantitative way the contributions of vacuum fluctuations and the radiation reaction to the generation of quantum entanglement and to the degradation of entangled states. We find that when the distance between two atoms larger than the characteristic length scale, the rate of variation of atomic energy in the de Sitter-invariant vacuum behaves differently compared with that in the thermal Minkowski spacetime. In particular, the generation and degradation of quantum entanglement can be enhanced or inhibited, which are dependent not only on the specific entangled state but also on the distance between the atoms.
In this paper, we investigate the behaviors of quantum correlation quantified by trace norm measurement-induced nonlocality (TMIN) for two uniformly accelerated atoms coupled with electromagnetic vacuum fluctuation in the Minkowski vacuum. We firstly discuss the solving process of master equation that governs the system evolution based on the Pauli matrix presentation for two-qubit state. Similar to [Y. Q. Yang et al., Phys. Rev. A 94, 032337 (2016)], we analyze the degradation, creation, revival and enhancement of quantum correlation for different initial states and polarizations of two atoms, and the influence of interatomic separation and acceleration on quantum correlation. Compared with the entanglement dynamics discussed in [Y. Q. Yang et al., Phys. Rev. A 94, 032337 (2016)], it is found that quantum correlation exhibits better robustness than entanglement. This may be helpful for quantum information processing.
We review the results obtained by investigating, in the framework of the theory of open systems based on completely positive quantum dynamical semigroups, the time evolution of quantum entanglement of two different bimodal systems, each one interacting with a thermal environment. The first system is formed of the free massless bosonic mode of a stationary observer in a region that is asymptotically flat (Kruskal observer) or freely falling in Schwarzschild black hole, and the mode of a uniformly accelerated observer hovering outside the event horizon of black hole. For initial bimodal Gaussian squeezed thermal states of the system, we show that under the influence of Hawking radiation the quantum entanglement of the two modes is destroyed in a finite time, for non-zero values of the temperature of the thermal environment, i.e. the phenomenon of entanglement sudden death takes place. The second system consists of two bosonic modes associated with a scalar quantum field in de Sitter space, characterized by two regions that are causally disconnected and described using open universe coordinates on two open charts. The survival time of the entanglement of this bimodal system strongly depends on the competition between the contrary effects provided by the squeezing of the initial bimodal state, the curvature of de Sitter space, the mass parameter and the thermal environment. It is shown that the entanglement is minimized for values 1/2 and 3/2 of the mass parameter, corresponding to the conformally coupled scalar field and, respectively, minimally coupled massless field.
We consider the time evolution of quantum entanglement in the context of interactions between atoms and the electromagnetic field. We explore the influence of interatomic separation and the degree to which this can change the qualitative character of those dynamics, including entanglement generation, protection, and sudden death (SD). We find that the qualitative features of entanglement dynamics can be changed entirely in few-mode models when atomic spacing is varied, allowing for particular choices of configuration that are favorable for maintaining entanglement. We also examine the inaccuracies introduced by the use of common approximations: We characterize unexpected errors that result from using perturbative master equations as well as those that result from using the rotating-wave approximation (RWA). We find that in dissipative systems the errors introduced by these approximations can lead to an incorrect picture of late-time dynamics. Standard perturbative master equations using the RWA are constrained to predict that late-time SD occurs to only some initial states at zero temperature, but this is merely an artifact of those approximation and generally not correct. The same master equations predict that at finite temperature all states are separable asymptotically at late times and must undergo SD. In fact a proper accounting of environmentally-induced corrections to the steady state of the system shows that for low temperatures it is possible to have asymptotic entanglement in some cases. We derive a master equation for two atoms interacting with the free field without using the RWA and solve it to obtain the dynamics, including the effects of distance. From these dynamics we find that, in fact, all initial states of atoms separated by any positive distance undergo SD even at zero temperature, though there are sub-radiant states that can be quite long-lived for closely spaced atoms.
We investigate the dynamics of quantum correlations such as entanglement and quantum discord between two noninteracting atoms, each of which is trapped inside one of two coupled cavities. We find that the cavity decay can induce both entanglement and quantum discord between the two atoms when they are initially prepared in doubly excited state. The result shows the sudden death and sudden birth of entanglement and robustness of the quantum discord to sudden death. It is also found that the doubly excited state is responsible for the sudden death of entanglement. Moreover, the sudden death of entanglement can be controlled by the intercavity hopping rate.