Fast Amplification and Rephasing of Entangled Cat States in a Qubit-Oscillator System

TL;DR

This paper introduces a method for rapidly creating and protecting large-amplitude entangled Schrödinger-cat states in a qubit-oscillator system with time-dependent coupling, effective even in deep-strong-coupling regimes.

Contribution

It presents a novel scheme for fast amplification and rephasing of entangled cat states, including protection against dephasing due to nonlinearity, in a qubit-oscillator system with variable coupling.

Findings

Effective generation of large-amplitude entangled cat states.

Protection scheme against dephasing from system nonlinearity.

Applicable across a wide range of coupling strengths, including deep-strong-coupling.

Abstract

We study a qubit-oscillator system, with a time-dependent coupling coefficient, and present a scheme for generating entangled Schr\"odinger-cat states with large mean photon numbers and also a scheme that protects the cat states against dephasing caused by the nonlinearity in the system. We focus on the case where the qubit frequency is small compared to the oscillator frequency. We first present the exact quantum state evolution in the limit of infinitesimal qubit frequency. We then analyze the first-order effect of the nonzero qubit frequency. Our scheme works for a wide range of coupling strength values, including the recently achieved deep-strong-coupling regime.