Improved speed limits for cavity-qubit operations using conditional displacements (Part 1)

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 show that because displacements do not change the extent of states in phase space, they do not lead to additional decoherence. Furthermore, optimizing pulses based on conditional displacements is tractable because the simulations can be carried out in a displaced frame. We explore whether significantly faster pulses than the standard speed limit can be found with usual coupling strengths, thereby avoiding decoherence during logical gates.