Fig. 1
From: Implementing a universal gate set on a logical qubit encoded in an oscillator
Experimental system and demonstration of control strategy. a Schematic drawing of the experimental system. A λ/4 coax-stub cavity resonator is coupled to a transmon and readout resonator on a sapphire substrate. Input couplers close to the transmon and cavity deliver the respective time-dependent microwave control fields ϵT(t) and ϵC(t). b Lower panel: optimized transmon and oscillator control waveforms of length approximately 2π/χ to take the oscillator from vacuum to the 6-photon Fock state. Solid (dotted) lines represent the in-phase (quadrature) field component. Upper panel: oscillator photon-number population trajectory vs. time conditioned on transmon in \(\left| g \right\rangle \). A complex trajectory occupying a wide range of photon numbers is taken to perform the intended operation. c Characterization of the oscillator state using Wigner tomography (bottom) and transmon spectroscopy (top), where grey dashed lines indicate the transition frequency associated with the first seven Fock states. The single peak in the spectroscopy data directly reveals the oscillator’s population due to the dispersive interaction giving a frequency shift of 6χ/2π ≈ 13 MHz
