Quantum information processing using multimode cavities

Multimode superconducting microwave cavities provide a hardware efficient means of engineering a large Hilbert space with high coherence, suitable for quantum simulations and information processing. Coupling to a superconducting transmon circuit results in random access control [1], with logic gates possible between arbitrary pairs of cavity modes. I will present our progress towards realizing such a processor using the quantum flute - a seamless rectangular 3D multimode cavity, with a tailored mode dispersion and lifetimes approaching a millisecond for ~10 modes. We present various schemes for controlling the cavity states using interactions mediated by the dispersively coupled transmon. 4-wave mixing processes induced by the non-linearity of the transmon can be used to exchange quantum states between the transmon and the cavity modes in a few hundred nanoseconds. When driven off-resonantly, these sideband drives can be used to controllably dress the cavity states, and engineer novel multimode interactions that are useful for quantum simulations. These interactions can also be used to compensate multimode-state-dependent Stark shifts, and perform generalized parity measurements, crucial for high fidelity gate operations and quantum error correction.

[1] Naik, R. K., et al. "Random access quantum information processors using multimode circuit quantum electrodynamics." Nature communications 8, 1904 (2017).