Fock State Generation and SWAP using a Rabi-Driven Qubit

Abstract: The deterministic generation and SWAP of Fock states in isolated high-Q modes form a core foundation for architectures in bosonic quantum computing. Conventionally, these operations necessitate strong coupling to a qubit, which inherently compromises the required cavity isolation. To address this trade-off, we introduce a tunable mechanism wherein a weakly coupled qubit, which preserves mode isolation, is driven to induce a strong interaction on demand. By leveraging a Rabi-driven, qubit-mediated sideband interaction, we realize on-demand Jaynes-Cummings coupling between a transmon and a long-lived cavity mode. Using a superconducting flute cavity with two high-Q modes, we deterministically demonstrate Fock state preparation up to n=5 at operation times of less than 2 microseconds per photon. We also demonstrate and characterize single-photon SWAP in approximately 2 microseconds. Finally, we adapt our SWAP method to generate a dual-rail Bell state. While current performance is constrained by baseline coherence rather than fundamental methodological limits, the protocol scales inherently to accommodate higher photon numbers and faster operational regimes. By enabling complex operations on modes that remain strictly weakly coupled to qubits, this approach establishes a robust pathway for advancing scalable bosonic quantum computing.