Showing papers by "Qiongyi He published in 2009"
TL;DR: In this article, a dynamical approach to quantum memories using an oscillator-cavity model is proposed, which overcomes the known difficulties of achieving high quantum input-output fidelity with long storage times compared to the input signal duration.
Abstract: We propose a dynamical approach to quantum memories using an oscillator-cavity model This overcomes the known difficulties of achieving high quantum input-output fidelity with long storage times compared to the input signal duration We use a generic model of the memory response, which is applicable to any linear storage medium ranging from a superconducting device to an atomic medium The temporal switching or gating of the device may either be through a control field changing the coupling, or through a variable detuning approach, as in more recent quantum memory experiments An exact calculation of the temporal memory response to an external input is carried out This shows that there is a mode-matching criterion which determines the optimum input and output pulse time evolution This optimum pulse shape can be modified by changing the gate characteristics In addition, there is a critical coupling between the atoms and the cavity that allows high fidelity in the presence of long storage times The quantum fidelity is calculated both for the coherent state protocol, and for a completely arbitrary input state with a bounded total photon number We show how a dynamical quantum memory can surpass the relevant classical memory bound, while retaining long storage times
27 citations
TL;DR: It is shown that arbitrary functions of continuous variables, e.g., position and momentum, can be used to generate tests that distinguish quantum theory from local hidden variable theories, and that optimized functional inequalities are resistant to standard forms of decoherence.
Abstract: We show that arbitrary functions of continuous variables, e.g., position and momentum, can be used to generate tests that distinguish quantum theory from local hidden variable theories. By optimizing these functions, we obtain more robust violations of local causality than obtained previously. We analytically calculate the optimal function and include the effect of nonideal detectors and noise, revealing that optimized functional inequalities are resistant to standard forms of decoherence. These inequalities could allow a loophole-free Bell test with efficient homodyne detection.
26 citations
TL;DR: A digital approach to quantum memories is proposed using a single-mode oscillator-cavity model, in which the coupling is shaped in time to provide the optimum interface to a time-symmetric input pulse.
Abstract: We propose a dynamical approach to quantum memories using a synchronous oscillator-cavity model, in which the coupling is shaped in time to provide the optimum interface to a symmetric input pulse. This overcomes the known difficulties of achieving high quantum input-output fidelity with storage times long compared to the input signal duration. Our generic model is applicable to any linear storage medium ranging from a superconducting device to an atomic medium. We show that with temporal modulation of coupling and/or detuning, it is possible to mode-match to time-symmetric pulses that have identical pulse shapes on input and output.
6 citations
TL;DR: In this paper, a single-mode oscillator-cavity model is proposed for quantum memories, in which the coupling is shaped in time to provide the optimum interface to a time-symmetric input pulse.
Abstract: We propose a digital approach to quantum memories using a single-mode oscillator-cavity model, in which the coupling is shaped in time to provide the optimum interface to a time-symmetric input pulse. Our generic model is applicable to any linear storage medium ranging from a superconducting device to an atomic medium.
5 citations