Impact of chaos on the excited-state quantum phase transition of the Kerr parametric oscillator

TL;DR

This paper investigates how chaos affects the excited-state quantum phase transition in the Kerr parametric oscillator, revealing that chaos destroys the ESQPT and the associated cat states, impacting quantum technology applications.

Contribution

It demonstrates how chaos from drive and nonlinearities destroys the ESQPT and cat states in the Kerr oscillator, informing future design of nonlinear quantum systems.

Findings

Chaos destroys the ESQPT in the Kerr oscillator.

Chaos eliminates the cat-like quantum states.

Analysis guides design of advanced nonlinear quantum devices.

Abstract

The driven Kerr parametric oscillator, of interest to fundamental physics and quantum technologies, exhibits an excited state quantum phase transition (ESQPT) originating in an unstable classical periodic orbit. The main signature of this type of ESQPT is a singularity in the level density in the vicinity of the energy of the classical separatrix that divides the phase space into two distinct regions. The quantum states with energies below the separatrix are useful for quantum technologies, because they show a cat-like structure that protects them against local decoherence processes. In this work, we show how chaos arising from the interplay between the external drive and the nonlinearities of the system destroys the ESQPT and eventually eliminates the cat states. Our results demonstrate the importance of the analysis of theoretical models for the design of new parametric oscillators with ever larger nonlinearities.