32,803 research outputs found

    Optimal transfer of an unknown state via a bipartite operation

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    A fundamental task in quantum information science is to transfer an unknown state from particle AA to particle BB (often in remote space locations) by using a bipartite quantum operation EAB\mathcal{E}^{AB}. We suggest the power of EAB\mathcal{E}^{AB} for quantum state transfer (QST) to be the maximal average probability of QST over the initial states of particle BB and the identifications of the state vectors between AA and BB. We find the QST power of a bipartite quantum operations satisfies four desired properties between two dd-dimensional Hilbert spaces. When AA and BB are qubits, the analytical expressions of the QST power is given. In particular, we obtain the exact results of the QST power for a general two-qubit unitary transformation.Comment: 6 pages, 1 figur

    Localization of Macroscopic Object Induced by the Factorization of Internal Adiabatic Motion

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    To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of interference, we invoke the adiabatic quantum entanglement between its collective states(such as that of the center-of-mass (C.M)) and its inner states based on our recent investigation. Under the adiabatic limit that motion of C.M dose not excite the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled state with correlation between adiabatic inner states and quasi-classical motion configurations of the C.M. Since the adiabatic inner states are factorized with respect to each parts composing the macroscopic object, this adiabatic separation can induce the quantum decoherence. This observation thus provides us with a possible solution to the Schroedinger cat paradoxComment: Revtex4,23 pages,1figur

    Magneto-Optical Stern-Gerlach Effect in Atomic Ensemble

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    We study the birefringence of the quantized polarized light in a magneto-optically manipulated atomic ensemble as a generalized Stern-Gerlach Effect of light. To explain this engineered birefringence microscopically, we derive an effective Shr\"odinger equation for the spatial motion of two orthogonally polarized components, which behave as a spin with an effective magnetic moment leading to a Stern-Gerlach split in an nonuniform magnetic field. We show that electromagnetic induced transparency (EIT) mechanism can enhance the magneto-optical Stern-Gerlach effect of light in the presence of a control field with a transverse spatial profile and a inhomogeneous magnetic field.Comment: 7 pages, 5 figure
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