Energy cat states induced by a parity-breaking excited-state quantum phase transition

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 Schrödinger 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 wavefunction in 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.

15 pages, 14 figures. To appear in Phys. Rev. A

References in corpus (11)

• Thermalization and its mechanism for generic isolated quantum systems
• Generalized Thermalization in an Integrable Lattice System
• Excited state quantum phase transitions in many-body systems
• Excited-state quantum phase transitions
• Impact of Quantum Phase Transitions on Excited Level Dynamics
• Excited-state quantum phase transition in the Rabi model
• Generation of macroscopic superposition states in ring superlattices
• Excited-state quantum phase transitions in systems with two degrees of freedom: III. Interacting boson systems
• Approximated integrability of the Dicke model
• Quantum phase transitions of atom-molecule Bose mixtures in a double-well potential
• Chaos in a deformed Dicke model