Quantum logic in waveguide quantum electrodynamics of artificial superconducting atoms - Design

In waveguide quantum electrodynamics (QED), a multi-levels system is required to maintains high coherence and allows strong interaction between qubit and propagating photons. Here, we propose a device with two fluxonium superconducting artificial atoms in a high pass waveguide filter. The waveguide filter has a high cutoff frequency such that the lowest two levels of fluxoniums at sweet spot can serve as computational levels. Owing to rich spectrum of fluxonium artificial atoms, Transitions above cutoff frequency of waveguide can have strong interaction with propagating photons. These high frequency transitions can provide readout and state transfer mechanism for the qubit states. Quantum logic operations can be implemented by conventional microwave control. With carefully designed fluxonium parameters, two qubit control-Z (CZ) gate can be realized via capacitive coupling. This device can be used as a building block of a hardware efficient quantum module in quantum internet.