Improved speed limits for cavity-qubit operations using conditional displacements (Part 2)*

It has been shown that universal control of an oscillator, realized here as a mode of a microwave cavity, can be achieved by coupling, in the strong-dispersive regime, the oscillator to an ancilla two-level system, such as a transmon [Heeres et al., 2017]. However, the rate of control appears to be limited by the interaction strength. In this two-part talk, we explore how displacements of the oscillator which are large on the scale of zero point fluctuations can generate an effective conditional displacement interaction [Campagne-Ibarcq et al., 2020], leading in turn to universal oscillator control with a speed limited by the oscillator drive strength rather than the strength of the oscillator-transmon coupling.

In this talk, we demonstrate how, even in the weak-dispersive regime, the conditional displacement gate can remain the generating gate of universal control. The advantage of working in this regime is that it minimizes unwanted nonlinearities and losses of the cavity due to the reverse Purcell effect. We also present practical pulse sequences that are robust against low-frequency transmon dephasing, as well as low-frequency amplitude drifts of the cavity drive.