Identification of quantum scars via phase-space localization measures

Abstract

There is no unique way to quantify the degree of delocalization of quantum states in unbounded continuous spaces. In this work, we explore a recently introduced localization measure that quantifies the portion of the classical phase space occupied by a quantum state. The measure is based on the $\alpha$-moments of the Husimi function and is known as the Rényi occupation of order $\alpha$. With this quantity and random pure states, we find a general expression to identify states that are maximally delocalized in phase space. Using this expression and the Dicke model, which is an interacting spin-boson model with an unbounded four-dimensional phase space, we show that the Rényi occupations with $\alpha >1$ are highly effective at revealing quantum scars. Furthermore, by analyzing the high moments ($\alpha >1$) of the Husimi function, we are able to identify qualitatively and quantitatively the unstable periodic orbits that scar some of the eigenstates of the model.

arXiv comment13 pages, 3 figures

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• Phenomenology of quantum eigenstates in mixed-type systems: lemon billiards with complex phase space structure
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