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Laser Physics Letters

Entanglement dynamic behavior of two driven coupled qubits

Jing Cheng, Xi Chen, Ji-Bing Liu, Yanxia Huang, Chuan-Jia Shan

Published Nov 30, 2018• 0 citations
Publisher

Abstract

Abstract We investigate the entanglement dynamic behavior of a system with two driven coupled qubits. The effects of the Rabi frequency ratio of nearest qubits, different initial states and different thermal boson number on quantum entanglement are addressed in detail. The results show that, whether the initial state is entangled or not, the two-qubit state will be in a stable entangled state when we select an appropriate parameter for the Rabi frequency ratio. Meanwhile, quantum sudden death and quantum sudden birth can happen in these systems. Increasing the noise strength can also put the system in a stable entanglement state. Hence steady-state entanglement can be obtained by adjusting the parameter of the Rabi frequency ratio and noise strength.

DOI
10.1088/1612-202x/aaf05f

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We analyze the dynamics of the entanglement in two independent non-Markovian channels. In particular, we focus on the entanglement dynamics as a function of the initial states and the channel parameters like the temperature and the ratio rrr between ω0ω_0ω0​ the characteristic frequency of the quantum system of interest, and ωcω_cωc​ the cut-off frequency of Ohmic reservoir. We give a stationary analysis of the concurrence and find that the dynamic of non-markovian entanglement concurrence Cρ(t)\mathcal{C}_ρ(t)Cρ​(t) at temperature kBT=0k_BT=0kB​T=0 is different from the kBT>0k_BT>0kB​T>0 case. We find that "entanglement sudden death" (ESD) depends on the initial state when kBT=0k_BT=0kB​T=0, otherwise the concurrence always disappear at finite time when kBT>0k_BT>0kB​T>0, which means that ESD must happen. The main result of this paper is that the non-Markovian entanglement dynamic is fundamentally different from the Markovian one. In the Markovian channel, entanglement decays exponentially and vanishes only asymptotically, but in the non-Markovian channel the concurrence Cρ(t)\mathcal{C}_ρ(t)Cρ​(t) oscillates, especially in the high temperature case. Then an open-loop controller adjusted by the temperature is proposed to control the entanglement and prolong the ESD time.
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We investigate the entanglement dynamical behavior of two coupled qubits via a Heisenberg XX interaction, which are connected with two independent finite temperature heat baths. By numerical simulations of the quantum master equation, it is found that the interesting phenomena of entanglement sudden death (ESD) as well as sudden birth (ESB) appear during the evolution process for particular initial states. We also show that two critical temperatures T 1 (determining that the quantum state is entangled or separable) and T 2 (where maximal stationary entanglement can be observed) exist, and stationary entanglement exhibits a non-monotonic behavior as a function of the finite temperature noise strength. These results enlarge the domain of the reasonable experimental temperature where stationary entanglement can be observable.
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