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

In waveguide quantum electrodynamics (QED), a multi-levels system can be used to simultaneously allow high coherence transitions and strong interaction with propagating photons in other transitions. Here, we demonstrate our experimental results on a device with two fluxonium superconducting artificial atoms in a waveguide. The waveguide filter has a high cutoff frequency such that the lowest two levels for both 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. We will demonstrate our measurement results of readout, coherent control of qubit transitions and two qubit control-Z (CZ) gate via capacitive coupling. Such devices can be used as a building block of a hardware efficient quantum module in quantum internet.