The Kerr-cat qubit: the Delta variant*

In this talk, I will present the experimental discovery of remarkable degeneracies in the spectrum of a Kerr oscillator subjected to a squeezing drive [1]. We find that when the detuning of the drive over the Kerr frequency is an even number 2m, the oscillator displays m+1 parity-protected spectral degeneracies that are insensitive to the drive amplitude. These tunable degeneracies stem from the unusual destructive interference of tunnel paths in a classically forbidden region [2] used to stabilize the Kerr-cat qubit [3,4]. Exploiting this interference, we created a new protected cat qubit [5] whose bias coherence peaks at the degeneracy condition and increases with the number of degeneracies. Our results illustrate the relationship between degeneracies and noise protection in quantum systems.

[1] Venkatraman & Cortiñas et al, arXiv:2211.04605

[2] Marthaler & Dykman PRA 76, 010102(R)

[3] Puri et al, npj QI 3, 18

[4] Grimm & Frattini et al, Nature 584

[5]  Ruiz et al, PRA 107, 042407