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Titre: Nullity of quantum discord of two-qubit X-state systems Auteur:Li, Gao-Xiang; Yi, Zhen; Ficek, Zbigniew Sujet:Quantum Physics Description:
The conditions are established for nullity of quantum discord for mixed states of a general two-qubit system whose dynamical behaviour is given by an X-state form density matrix. It is found that quantum discord can vanish at a finite time even in the presence of correlations between qubits. The degeneracy of the populations of the combined states of the qubits and the multi-qubit quantum coherences are shown to be responsible for vanishing of the discord. We illustrate our considerations by examining the coherent-state Tavis-Cummings model in which two qubits interact dispersively with the cavity field. The disappearance of the discord is shown to be dependent on the initial atomic conditions that it may occur at a discrete instance or periodically at discrete instances redistributed over whole range of the evolution time. The nullity of the discord is interpreted as resulting from equal preparation of the spin anti-correlated and spin correlated product states in superposition~states. Comment: 5 pages, 3 figures
1101.4983 (ARXIV ID)
Titre: Ground-state cooling of a mechanical resonator by single- and two-phonon processes Auteur:Zhu, Jia-Pei; Li, Gao-Xiang Sujet:Articles Description:
A scheme for ground-state cooling of a mechanical resonator by single- and two-phonon processes is analyzed. The mechanical resonator is coupled to two coupled quantum dots forming an effective Λ-type three-level structure and connected with two normal metal leads. The quantum dots are driven by two light fields; by choosing appropriate parameters, the electron can be trapped in the dark state of the system, a superposition of the two ground states. When the single-phonon absorption and emission processes are dominant, under the weak (strong) driving field circumstances, the mechanical resonator is cooled through absorbing a phonon when the electron jumps from dark state to bright state (one of the dressed states) and then tunnels out of the two coupled dots. Net cooling of the resonator to its ground state is possible in the absence of the electron-phonon dephasing via single-phonon processes. When the two-phonon processes are tuned to be stronger than the single-phonon processes, the mechanical resonator can be cooled to its nonclassical state.
Fait partie de:
Journal of Applied Physics, 01 February 2012, Vol.111(3)
0021-8979 (ISSN); 1089-7550 (E-ISSN); 10.1063/1.3679541 (DOI)
Creation of pure multi-mode entangled states in a ring cavity
Li, Gao-Xiang, Ficek, Zbigniew
Optics communications, 2010, Vol.283(5), pp.814-821
[Revue évaluée par les pairs]
Titre: Polychromatic quadripartite entanglement from concurrent four-wave mixing in a three-level atomic system Auteur:Tan, Hua-Tang; Li, Gao-Xiang Sujet:Classical And Quantum Mechanics, General Physics Atomic And Molecular Physicsatoms ; Cavity Resonators ; Energy Levels ; Frequency Mixing ; Quantum Entanglement ; Quantum Mechanics ; Quantum States; Description:
In this paper, we investigate the generation of polychromatic quadripartite entanglement of continuous variables from a three-level Λ-type atomic system inside an optical quadruply resonant cavity. The atoms are driven by external lasers and simultaneously coupled to four cavity modes by means of multiply concurrent four-wave mixing interactions. The general master equation of the cavity field is derived explicitly. By solving the Gaussian-type master equation and using the negative-partial-transpose criterion for bipartite entanglement, we show that the genuine quadripartite entanglement of the field can be generated over a wide range of parameters. The entanglement properties of the four-mode field are discussed in detail. We find that the optimal quadripartite entanglement can be obtained when the cavity modes are tuned to be resonant with the Rabi sidebands of the driven atoms. Journal Article.
Fait partie de:
Physical Review A, 9/2010, Vol.82(3)
1050-2947 (ISSN); 1094-1622 (E-ISSN); http (DOI)