Oral: Fast and High-Fidelity SNAP Gate for Cavities Controlled by Weakly Coupled Ancilla

Superconducting cavities with high quality factors, coupled to a nonlinear ancilla, present a promising platform for storing and manipulating quantum information. A commonly used control protocol for such systems is the selective number-dependent arbitrary phase (SNAP) gate, where the gate time is governed by the dispersive interaction between the cavity and the ancilla. This constraint poses challenges for controlling ultra-high-coherence cavities (10–100 ms relaxation times), as the lossier ancilla must be weakly coupled to avoid Purcell-limiting the cavity's coherence and to minimize backaction from ancilla bit flips. Here, we propose a novel method for achieving a high-fidelity SNAP gate with gate times shorter than those typically set by the bare dispersive shift. We present both numerical simulations and analytical derivations validating the effectiveness of our protocol. These results offer a pathway toward experimentally realizing high-fidelity control of cavity modes, particularly in systems with weakly coupled, high-coherence cavities.