Quantum information processing using 3D multimode circuit QED*

Multimode superconducting microwave cavities provide a hardware efficient means of engineering a large, high-coherence Hilbert space suitable for quantum information processing. When coupled to a superconducting transmon circuit, they can be used to construct random access quantum processors in which logic gates can be performed between arbitrary pairs of cavity modes via sideband transitions with the transmon [1]. We present our progress toward realizing such a processor using a seamless rectangular 3D multimode cavity - the quantum flute, with a tailored mode dispersion and decay times around a millisecond for tens of cavity modes. To eliminate coherent errors arising from multimode state dependent Stark shifts of the transmon, we introduce an intermediate single-mode 'manipulate' cavity with a tunable coupling to the multimode cavity.

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