部分极化部分退极化自旋1/2系统的集体不确定性
Collective Uncertainty in Partially-Polarized and Partially-Decohered Spin-1/2 Systems
摘要：
通常的做法是将大自旋系综建模为具有总角动量J = N x j的有效赝自旋，其中j是每个粒子的自旋。这种方法（至少是隐含地）将系综的量子态限制在所谓的对称希尔伯特空间。在这里，我们认为，对称状态下的典型的实验涉及大云的原子或离子的退相干类型一般不保存完好。特别是，对称状态下的退相干模型，作用相同，但本地的不同成员的合奏迅速退化。使用一种方法[Phys. Rev. A 78，052101（2008）]，不限于对称希尔伯特空间，我们探索潜在的陷阱，在设计和解释的实验自旋压缩和集体原子现象时，对称状态的属性扩展到系统，他们不适用。
英文摘要：
It has become common practice to model large spin ensembles as an effective pseudospin with total angular momentum J = N x j, where j is the spin per particle. Such approaches (at least implicitly) restrict the quantum state of the ensemble to the so-called symmetric Hilbert space. Here, we argue that symmetric states are not generally well-preserved under the type of decoherence typical of experiments involving large clouds of atoms or ions. In particular, symmetric states are rapidly degraded under models of decoherence that act identically but locally on the different members of the ensemble. Using an approach [Phys. Rev. A 78, 052101 (2008)] that is not limited to the symmetric Hilbert space, we explore potential pitfalls in the design and interpretation of experiments on spin-squeezing and collective atomic phenomena when the properties of the symmetric states are extended to systems where they do not apply.
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