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arXiv:1704.02811

Thermal Entanglement, Specific Heat and Quantum Discord in Open Quantum Systems Including Non-Markovian Processes

Behzad Lari, HASSAN HASSANABADI

Published Apr 10, 2017• 1 citation

Abstract

Entanglement (EN) is a determinative correlation in designation of quantum gates and quantum memories. All quantum operations which are assembled by quantum circuits, are exposed to environment. However, quantum discord (QD) as a new key of resource for quantum information theory is in spotlight of research. Therefore, the study of EN and QD in open quantum systems seems to be important. In this Brief Report, We derived a formula for specific heat of the principle system as a part of open quantum system (in special for Jaynes-Cumming regime), and we looked for relations between entanglement and specific heat which is important for designing of the quantum memory. We also studied the dynamics of thermal EN and QD in Jaynes-Cumming regime including the Non-Markovian processes via Born-Markove approximation and obtained a regions of temperature and coupling constant between parts of systems which the entanglement of formation had a stable behavior .It seems to be useful to design the quantum gates. We observed the negative and divergence specific heat (in contradiction with third law of thermodynamics) in low temperature because the state of open system is entangle. According to obtained results, we did not find out any violence oscillation in quantum discord and because entanglement decreases with respect time, fast response to inputs is crucial for assembling quantum circuits and quantum memory.

DOI: 10.48550/arxiv.1704.02811

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Entanglement (EN) is a determinative correlation in designation of quantum gates and quantum memories. All quantum operations which are assembled by quantum circuits, are exposed to environment. However, quantum discord (QD) as a new key of resource for quantum information theory is in spotlight of research. Therefore, the study of EN and QD in open quantum systems seems to be important. In this Brief Report, We derived a formula for specific heat of the principle system as a part of open quantum system (in special for Jaynes-Cumming regime), and we looked for relations between entanglement and specific heat which is important for designing of the quantum memory. We also studied the dynamics of thermal EN and QD in Jaynes-Cumming regime including the Non-Markovian processes via Born-Markove approximation and obtained a regions of temperature and coupling constant between parts of systems which the entanglement of formation had a stable behavior .It seems to be useful to design the quantum gates. We observed the negative and divergence specific heat (in contradiction with third law of thermodynamics) in low temperature because the state of open system is entangle. According to obtained results, we did not find out any violence oscillation in quantum discord and because entanglement decreases with respect time, fast response to inputs is crucial for assembling quantum circuits and quantum memory.

Dynamics of an open two-qubit system is investigated in the post-Markovian regime, where the environments have a short-term memory. Each qubit is coupled to separate environment which is held in its own temperature. The inter-qubit interaction is modeled by XY-Heisenberg model in the presence of spin-orbit interaction and inhomogeneous magnetic field. The dynamical behavior of entanglement and discord has been considered. The results show that, quantum discord is more robust than quantum entanglement, during the evolution. Also the asymmetric feature of quantum discord can be monitored by introducing the asymmetries due to inhomogeneity of magnetic field and temperature difference between the reservoirs. By employing proper parameters of the model, it is possible to maintain non-vanishing quantum correlation at high degree of temperature. The results can provide a useful recipe for studying of dynamical behavior of two-qubit systems such as trapped spin-electrons in coupled quantum dots.

By considering a double Jaynes—Cummings model, we investigate the dynamics of quantum correlations, such as the quantum discord and the entanglement, for two atoms in their respective noisy environments, and study the effect of the purity and the cavity temperature on the quantum correlations. The results show that the entanglement suffers sudden death and revival, however the quantum discord can still reveal the quantum correlations between the two atoms in the region where the entanglement is zero. Moreover, when the temperature of each cavity is high the entanglement dies out in a short time, but the quantum discord still survives for quite a long time. It means that the quantum discord is more resistant to environmental disturbance than the entanglement at higher temperatures.

Knowledge of the dynamical behavior of correlations with no classical counterpart, like entanglement, nonlocal correlations and quantum discord, in open quantum systems is of primary interest because of the possibility to exploit these correlations for quantum information tasks. Here we review some of the most recent results on the dynamics of correlations in bipartite systems embedded in non-Markovian environments that, with their memory effects, influence in a relevant way the system dynamics and appear to be more fundamental than the Markovian ones for practical purposes. Firstly, we review the phenomenon of entanglement revivals in a two-qubit system for both independent environments and a common environment. We then consider the dynamics of quantum discord in non-Markovian dephasing channel and briefly discuss the occurrence of revivals of quantum correlations in classical environments.

We show the special dynamic characteristic of Gaussian quantum discord, exhibited by two-mode Gaussian symmetric squeezed thermal states (STS) in continuous-variable (CV) systems with a common non-Markovian environment, is denitely dierent from Markov processes.We demonstrate that Gaussian quantum discord can be created whenever the information ow from environment back to the system.We also show that the rate of decrease for Gaussian quantum discord is related to the coupling constant.We discover that the initial value of Gaussian quantum discord is determined by the average number of thermal photons of the system.

In this paper, the density matrix is obtained using the non-Markovian master equation method for a system consisting of two-qubit modeling with the Heisenberg XXZ chain, which involves the Dzyaloshinskii–Moriya interaction and is exposed to the bosonic baths. Also, using the proposed formula for calculating the specific heat through the density matrix of the open quantum system, the specific heat is calculated. The quantum entanglement behavior with time and coupling constant is investigated. It is observed that the specific heat at low temperatures becomes negative when the system is exposed to the environment. The time behavior of quantum entanglement for this model showed that the entanglement decreases to zero with increasing time.

We study the dynamic of the Gaussian quantum discord in a continuous-variable system subject to a common non-Markovian environment with zero-temperature. By considering an initial two-mode Gaussian symmetric squeezed thermal state, we show that Gaussian discord has a very different dynamic characteristic in a non-Markovian evolution versus a Markov process, and can be created by the memory effect, which features non-Markovianity. We also study the relationship between Gaussian discord and the non-Markovian degree of the environment. The results may offer us an effective experimental method to get more quantum correlations.