arXiv:2406.03389 · Science Advances

Hot Schrödinger cat states

Ian Yang, Thomas E. G. Agrenius, Vasilisa Usova, Oriol Romero‐Isart, Gerhard Kirchmair

Published Apr 4, 2025• 11 citations

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 nonclassical state originating from a mixed state, using 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" Schrödinger cat states for an initial purity as low as 0.06. This corresponds to a cavity mode temperature of up to 1.8 kelvin, 60 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.

DOI: 10.1126/sciadv.adr4492

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