开放量子系统纯态系综的不等式：优选系综是那些物理上可实现的系综
Inequivalence of pure state ensembles for open quantum systems: the preferred ensembles are those that are physically realizable
摘要：
处于稳态的开放量子系统$\hatρ_{ss}$可以用纯态$\hatρ_{ss}=\sum_{k}\wp_{k}\ket{ψ_k} \bra{ψ_k}$的加权系综以无限多种方式表示。物理上可实现的系综是这样一种系综，即对环境的某些连续测量将使系统坍缩成纯态$\ket{ψ(t)}$，随机演化使得$\ket{ψ(t)} = \ket{ψ_{k}}$等于$\wp_{k}$的时间比例。一些，但不是所有的，合奏是公关。这构成了首选合奏事实，与公关合奏是首选合奏。给出了一个系综为PR的充要条件，并通过原子激光相干态系综不为PR的例子说明了这种方法。
英文摘要：
An open quantum system in steady state $\hatρ_{ss}$ can be represented by a weighted ensemble of pure states $\hatρ_{ss}=\sum_{k}\wp_{k}\ket{ψ_k} \bra{ψ_k}$ in infinitely many ways. A physically realizable (PR) ensemble is one for which some continuous measurement of the environment will collapse the system into a pure state $\ket{ψ(t)}$, stochastically evolving such that the proportion of time for which $\ket{ψ(t)} = \ket{ψ_{k}}$ equals $\wp_{k}$. Some, but not all, ensembles are PR. This constitutes the preferred ensemble fact, with the PR ensembles being the preferred ensembles. We present the necessary and sufficient conditions for a given ensemble to be PR, and illustrate the method by showing that the coherent state ensemble is not PR for an atom laser.
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