Hot Schrödinger Cat States

The observation of quantum phenomena often necessitates sufficiently pure states, a requirement that can be challenging to achieve.

In this study, we prepare a non-classical state originating from a mixed state, utilising dynamics that preserve the initial purity of the state (i.e. without removing entropy or purifying the system with measurement). We generate a Schrödinger cat state within a circuit quantum electrodynamics setup [1], in which a transmon is coupled to a high coherence microwave cavity. We initialise the cavity with a thermal state of up to n_th=7.6(2) average photons, equalling a purity of 0.05 or a mode temperature of up to 1.8 Kelvin, which is sixty times hotter than its physical environment. Hot Schrödinger's cat states are deterministically prepared with two protocols [2,3]. Our realisation of non-pure but quantum coherent superposition states could guide the preparation of similar states in other continuous-variable quantum systems. Wigner function measurements confirm the quantum coherent nature of the prepared states through the observation of interference fringes and Wigner negativities.

References:

1. M. Reagor et al., Phys. Rev. B, 94 (2016) 014506

2. Z. Leghtas et al., Phys. Rev. A, 87 (2013) 042315

3. A. Eickbusch et al., Nat. Phys. 18 (2022) 1464-1469