The Kerr-Cat Qubit: Stabilization, Readout, and Gates.

Superpositions of two opposite-phase coherent states in an oscillator, so-called Schrödinger-cat states, can be used to encode a qubit protected against phase-flip errors. Such a protected “cat qubit” has the potential to significantly reduce the overhead associated with quantum error correction. However, the practical operation of a cat qubit faces several challenges: Its basis states are highly excited states of the oscillator and need to be stabilized in order to maintain the protection. At the same time, the system has to be compatible with fast gates on the encoded qubit and a quantum non-demolition (QND) readout of the encoded information.

In this talk, we will present our recent experimental results on the stabilization of an error-protected cat qubit through the interplay between Kerr nonlinearity and single-mode squeezing in a superconducting microwave resonator. Our experiment demonstrates a full set of single-qubit gates and QND-readout on timescales significantly shorter than the relevant decoherence times.