Energy cat states induced by a parity-breaking excited-state quantum phase transition
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2022
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Corps, Angel L.
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Amer Physical Soc
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Abstract
We show that excited-state quantum phase transitions (ESQPTs) in a system in which the parity symmetry is broken can be used to engineer an energy cat state???a Schr??dinger cat state involving a quantum superposition of both different positions and energies. By means of a generalization of the Rabi model, we show that adding a parity-breaking term annihilates the ground-state quantum phase transition between normal and superradiant phases, and induces the formation of three excited-state phases, all of them identified by means of an observable with two eigenvalues. In one of these phases, level crossings are observed in the thermodynamic limit. These allow us to separate a wave function into two parts: one, with lower energy, trapped within one region of the spectrum, and a second one, with higher energy, trapped within another. Finally, we show that a generalized microcanonical ensemble, including two different average energies, is required to properly describe equilibrium states in this situation. Our results illustrate yet another physical consequence of ESQPTs.
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©2022 American Physical Society. We gratefully thank F. Pérez-Bernal and J. Dukelsky for insightful discussions. This work has been supported by the Spanish Grant No. PGC-2018-094180-B-I00 funded by Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación MCIN/AEI/10.13039/501100011033 and FEDER "A Way of Making Europe." A.L.C. acknowledges financial support from "la Caixa" Foundation (Grant No. 100010434) through the fellowship LCF/BQ/DR21/11880024.