Hot Schr\"odinger Cat States

TL;DR

This paper demonstrates creating and measuring highly mixed, 'hot' Schr"odinger cat states in a microwave cavity, showing quantum superpositions can exist at much higher temperatures than previously possible.

Contribution

It introduces a method to generate and observe quantum superpositions from highly mixed states using unitary interactions, expanding the conditions under which quantum phenomena can be studied.

Findings

Successfully created superpositions with initial purity as low as 0.06

Achieved states corresponding to temperatures up to 1.8 Kelvin

Demonstrated the feasibility of observing quantum effects in hot, mixed states

Abstract

The observation of quantum phenomena often necessitates sufficiently pure states, a requirement that can be challenging to achieve. In this study, our goal is to prepare a non-classical state originating from a mixed state, utilizing dynamics that preserve the initial low purity of the state. We generate a quantum superposition of displaced thermal states within a microwave cavity using only unitary interactions with a transmon qubit. We measure the Wigner functions of these ``hot'' Schr\"odinger cat states for an initial purity as low as 0.06. This corresponds to a cavity mode temperature of up to 1.8 Kelvin, sixty times hotter than the cavity's physical environment. Our realization of highly mixed quantum superposition states could be implemented with other continuous-variable systems e.g. nanomechanical oscillators, for which ground-state cooling remains challenging.