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arXiv 2104.14942quant-phastro-ph.COgr-qc
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四模压缩态:双场量子系统和辛群$\mathrm{Sp}(4,\mathbb{R})$

Four-mode squeezed states: two-field quantum systems and the symplectic group $\mathrm{Sp}(4,\mathbb{R})$

Thomas Colas, Julien Grain, Vincent Vennin

摘要:

我们构造了四模压缩态并研究了它们的物理性质。这些状态描述了两个线性耦合的量子标量场,这使得它们在物理上与宇宙学等各种背景相关。它们概括了通常的双模压缩状态的单场系统,与额外的转移的量子之间的字段。为了在Fock空间中建立它们,我们使用相空间的辛结构。为此,我们首先对辛群$\mathrm{Sp}(4,\mathbb{R})$及其李代数进行了教学分析,由此构造了四模压缩态并讨论了它们的结构。我们还研究了由两个场中的一个跟踪得到的约化单场系统。这一过程是更容易在相空间中,它激励使用的维格纳函数,我们介绍作为一种替代的描述状态。它允许我们讨论线性相互作用情况下的环境效应。特别是,我们发现,总是有一个范围内的相互作用耦合的消相干发生,而不影响系统的功率谱(因此可观的)。

英文摘要:

We construct the four-mode squeezed states and study their physical properties. These states describe two linearly-coupled quantum scalar fields, which makes them physically relevant in various contexts such as cosmology. They are shown to generalise the usual two-mode squeezed states of single-field systems, with additional transfers of quanta between the fields. To build them in the Fock space, we use the symplectic structure of the phase space. For this reason, we first present a pedagogical analysis of the symplectic group $\mathrm{Sp}(4,\mathbb{R})$ and its Lie algebra, from which we construct the four-mode squeezed states and discuss their structure. We also study the reduced single-field system obtained by tracing out one of the two fields. This procedure being easier in the phase space, it motivates the use of the Wigner function which we introduce as an alternative description of the state. It allows us to discuss environmental effects in the case of linear interactions. In particular, we find that there is always a range of interaction coupling for which decoherence occurs without substantially affecting the power spectra (hence the observables) of the system.

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