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 Chin. Phys. B, 2014, Vol. 23(12): 120305    DOI: 10.1088/1674-1056/23/12/120305
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# Preparation of optimal entropy squeezing state of atomic qubit inside the cavity via two-photon process and manipulation of atomic qubit outside the cavity

Zhou Bing-Ju, Peng Zhao-Hui, Jia Chun-Xia, Jiang Chun-Lei, Liu Xiao-Juan
College of Physics and Electronic Science, Hunan University of Science and Technology, Xiangtan 411201, China
Abstract  Considering two atomic qubits initially in Bell states, we send one qubit into a vacuum cavity with two-photon resonance and leave the other one outside. Using quantum information entropy squeezing theory, the time evolutions of the entropy squeezing factor of the atomic qubit inside the cavity are discussed for two cases, i.e., before and after rotation and measurement of the atomic qubit outside the cavity. It is shown that the atomic qubit inside the cavity has no entropy squeezing phenomenon and is always in a decoherent state before the operating atomic qubit outside the cavity. However, the periodical entropy squeezing phenomenon emerges and the optimal entropy squeezing state can be prepared for the atomic qubit inside the cavity by adjusting the rotation angle, choosing the interaction time between the atomic qubit and the cavity, controlling the probability amplitudes of subsystem states. Its physical essence is cutting the entanglement between the atomic qubit and its environment, causing the atomic qubit inside the cavity to change from the initial decoherent state into maximum coherent superposition state, which is a possible way of recovering the coherence of a single atomic qubit in the noise environment.
Keywords:  atomic qubit      rotation operation      optimal entropy squeezing state      two-photon process
Received:  15 May 2014      Revised:  13 June 2014      Accepted manuscript online:
 PACS: 03.65.Ud (Entanglement and quantum nonlocality) 03.67.-a (Quantum information) 42.50.Pq (Cavity quantum electrodynamics; micromasers)
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 11374096 and 11405052).
Corresponding Authors:  Liu Xiao-Juan     E-mail:  lxjdx1987@163.com