Schrödinger cat in a Kerr-free SNAIL-terminated resonator

Schrödinger cat states offer variety of application in quantum information processing [1]. Schrödinger cat states were normally observed in 3D cavity with permanent Kerr nonlinearity [2] or concurrent squeezing drive [1]. However, the nonlinearity from the ancillary qubit may induce the collapse of the cat states. Here, we demonstrate a method to generate Schrödinger cat states in a coplanar SNAIL-terminated resonator biased at Kerr-free point. To manipulate and stabilize the non-classical superposition of microwave coherent states, we apply a pulse to tune the Kerr coefficient fastly. Through this strategy, multi-component Schrödinger cat states can be implanted and maintained passively without additional microwave signal. Wigner function measurement on the cat state via an ancillary transmon qubit verifies the fidelity and evolution processes of the non-classical states of microwave field. Our result shows the potential of a scalable 2D structure for the continuous-variable quantum computing based on Schrödinger cats.

[1]. A. Grimm et al., Stabilization and operation of a Kerr-cat qubit, Nature 584, 205-209 (2020).
[2]. G. Kirchmair et al., Observation of quantum state collapse and revival due to the single-photon Kerr effect, Nature 495, 205–209 (2013).