Mediating interactions between superconducting microwave cavities with three-wave mixing, part 1*

Engineering tunable bilinear couplings between microwave cavities provides a way to manipulate and entangle long-lived quantum states. Two-cavity gates, such as the beam splitter and exponential SWAP (eSWAP), have been successfully demonstrated using a driven transmon coupled to both cavities. However, the fidelity of these gates is limited by unwanted 4th order processes such as the AC Stark effect. By replacing the transmon’s Josephson junction with a superconducting nonlinear asymmetric inductive element (SNAIL), we produce a bilinear interaction via its 3rd order nonlinearity while minimizing 4th order effects. This is expected to offer high fidelity two-cavity gates using all-RF control. I will discuss experimental design considerations and the theory behind the coupled-cavity device.