Overcoming decoherence of cat-states formed in a cavity using squeezed-state inputs

TL;DR

This paper demonstrates that coupling a cavity system to a squeezed reservoir significantly prolongs the lifetime and enhances the quality of microwave cavity cat states, even under thermal noise, advancing quantum technology applications.

Contribution

It shows that squeezed reservoirs can lengthen cat state lifetimes and improve their coherence, providing a new method to mitigate decoherence in microwave quantum systems.

Findings

Squeezed states extend cat state lifetime.

Squeezing improves cat state quality in microwave cavities.

Thermal decoherence can be mitigated by reservoir squeezing.

Abstract

A cat-state is a superposition of two coherent states with amplitudes $\alpha_{0}$ and $-\alpha_{0}$. Recent experiments create cat states in a microwave cavity field using superconducting circuits. As with degenerate parametric oscillation (DPO) in an adiabatic and highly nonlinear limit, the states are formed in a signal cavity mode via a two-photon dissipative process induced by the down conversion of a pump field to generate pairs of signal photons. The damping of the signal and the presence of thermal fluctuations rapidly decoheres the state, and the effect on the dynamics is to either destroy the possibility of a cat state, or else to sharply reduce the lifetime and size of the cat-states that can be formed. In this paper, we study the effect on both the DPO and microwave systems of a squeezed reservoir coupled to the cavity. While the threshold nonlinearity is not altered, we show that the use of squeezed states significantly lengthens the lifetime of the cat states. This improves the feasibility of generating cat states of large amplitude and with a greater degree of quantum macroscopic coherence, which is necessary for many quantum technology applications. Using current experimental parameters for the microwave set-up, which requires a modified Hamiltonian, we further demonstrate how squeezed states enhance the quality of the cat states that could be formed in this regime. Squeezing also combats the significant decoherence due to thermal noise, which is relevant for microwave fields at finite temperature. By modeling a thermal squeezed reservoir, we show that the thermal decoherence of the dynamical cat states can be inhibited by a careful control of the squeezing of the reservoir. To signify the quality of the cat state, we consider different signatures including fringes and negativity, and the $C_{l_{1}}$ measure of quantum coherence.