Fast, high-fidelity multi-mode operations between microwave resonators are an important tool for bosonic quantum computation and simulation with superconducting circuits. An attractive approach for implementing these operations is to couple these resonators via a non-linear mixer and actuate parametric processes with RF drives. It can be challenging to make these processes simultaneously fast and high fidelity, since this requires introducing strong drives without compromising the cavity lifetimes or introducing additional decoherence channels. We propose that the symmetry of the mixing device can enforce a selection rule we call ’parity protection’, which suppresses unwanted nonlinear interactions that would otherwise introduce decoherence or degrade performance. Exploiting this principle, we create a parity-protected mixer with two orthogonal modes that are coupled to the drive and a pair of high-Q cavities respectively. This lets us drive a fast, highly coherent beamsplitter between the cavities, limited primarily by their intrinsic single-photon loss. We characterize this beamsplitter in the dual-rail subspace and show that we can detect and select out this loss to achieve an average gate fidelity exceeding 99.99%, which to our knowledge far exceeds the current state of the art.
Speaker: Dr. Yao Lu, Postdoctoral Associate, Yale University
Host: Jens Koch
Joan West
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