A quantum state router based on parametrically driven photon exchange.*

Precisely controlled couplings between qubits are a vital part of all quantum information processing. For superconducting qubits, most efforts seek to implement a “surface code” architecture, which only couples nearest-neighbor qubits. However, longer range couplings are very desirable as they reduce the overhead of interactions between distant qubits. We present a design that can realize long range couplings between qubits through a modular quantum router. The design contains a 3D superconducting waveguide ‘trunk’ of microwave modes and a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) to generate parametric photon exchange couplings between each pair of modes. We couple individual modules via a communication cavity deliberately detuned from a corresponding waveguide mode. Quantum information is exchanged between modules by driving the SNAIL at the difference of the communication modes’ frequencies. We will present experimental results on fast all-to-all coherent photon SWAPs between arbitrary cavity pairs, as well as multiple, simultaneous SWAPs. We will also discuss our efforts to engineer longer mode lifetimes in the router and design filters to enable stronger pumping and faster SWAP gates.