arXiv 0810.50342008-10quant-phcond-mat.stat-mech

两量子比特开放系统与压缩热浴相互作用中的量子非破坏纠缠动力学

Entanglement Dynamics in Two-Qubit Open System Interacting with a Squeezed Thermal Bath via Quantum Nondemolition interaction

Subhashish Banerjee, V. Ravishankar, R. Srikanth

备注：: 17 pages, 9 figures, REVTeX4
发表信息：: European Physical Journal D 56, 277 (2010)
DOI：: 10.1140/epjd/e2009-00286-2

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摘要：

我们分析了两个量子比特系统与初始压缩热环境通过量子非破坏系统-储层相互作用相互作用的纠缠动力学，假设系统和储层最初是可分离的。我们比较和对比的情况下，量子位是相互接近的（“集体制度”）或远离（“本地化制度”）相对于环境的空间变化的两个量子位系统的消相干。突然死亡的纠缠（如并发量化）是发生在本地化的情况下，而不是在集体的情况下，纠缠往往“环下来”。这种相互作用的QND特性的结果是贝尔态的时间演化保真度永远不会低于$1/\sqrt{2}$，这一事实对于量子通信应用（如量子中继器）是有用的。使用一种新的量化的混合态纠缠，我们表明，有噪声制度，即使纠缠消失，状态仍然是可用于应用程序，如NMR量子计算，因为伪纯成分的存在。

英文摘要：

We analyze the dynamics of entanglement in a two-qubit system interacting with an initially squeezed thermal environment via a quantum nondemolition system-reservoir interaction, with the system and reservoir assumed to be initially separable. We compare and contrast the decoherence of the two-qubit system in the case where the qubits are mutually close-by (`collective regime') or distant (`localized regime') with respect to the spatial variation of the environment. Sudden death of entanglement (as quantified by concurrence) is shown to occur in the localized case rather than in the collective case, where entanglement tends to `ring down'. A consequence of the QND character of the interaction is that the time-evolved fidelity of a Bell state never falls below $1/\sqrt{2}$, a fact that is useful for quantum communication applications like a quantum repeater. Using a novel quantification of mixed state entanglement, we show that there are noise regimes where even though entanglement vanishes, the state is still available for applications like NMR quantum computation, because of the presence of a pseudo-pure component.

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