Understanding the degradation of Kerr cat qubit's noise bias

The Kerr cat qubit has been experimentally demonstrated to achieve significant noise bias due to the large separation in phase space between its logical states. While the bit-flip time between cat states decreases inversely with photon number, the phase-flip time increases significantly. To establish high noise bias in a Kerr cat qubit, a nonlinear resonator is subjected to a strong drive in the gigahertz range. While for extremely high drive strength the nonlinear oscillator becomes chaotic and cat states cease to exist [1,2], it is less clear what limits the growth of the Kerr cat at more moderate drives. Although recent advances have explained the staircase-like increase in phase-flip time [3,4], a recent experiment revealed that this increase unexpectedly stops after reaching just ten photons [5]. Motivated by this observation, this talk will explore the limits of the Kerr cat qubit operating in the regime of this experiment.