二能级原子任意纯态的反馈稳定
Feedback-stabilization of an arbitrary pure state of a two-level atom
摘要：
利用单位效率零拍探测方法，将二能级原子的量子态坍缩到布洛赫球上的随机动点。最近，Hofmann、Mahler和Hess [Phys.Rev.A { \bf 57}，4877（1998）]表明，通过使相干驱动的一部分与零差光电流成比例，可以将状态稳定到球的下半部分上的任何点。在这里，我们重新分析他们的建议，使用随机主方程的技术，允许他们的结果以两种方式推广。首先，我们表明，任何点的上半部分或下半部分，但不是赤道，球可以稳定。其次，我们考虑非单位效率检测，并通过计算在布洛赫空间中的任何特定方向上可获得的最大纯度来量化反馈的有效性。
英文摘要：
Unit-efficiency homodyne detection of the resonance fluorescence of a two-level atom collapses the quantum state of the atom to a stochastically moving point on the Bloch sphere. Recently,Hofmann, Mahler, and Hess [Phys. Rev. A {\bf 57}, 4877 (1998)] showed that by making part of the coherent driving proportional to the homodyne photocurrent can stabilize the state to any point on the bottom half of the sphere. Here we reanalyze their proposal using the technique of stochastic master equations, allowing their results to be generalized in two ways. First, we show that any point on the upper or lower half, but not the equator, of the sphere may be stabilized. Second, we consider non-unit-efficiency detection, and quantify the effectiveness of the feedback by calculating the maximal purity obtainable in any particular direction in Bloch space.
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