Fig. 3: Superimposed microwave emission.
From: A cryogenic on-chip microwave pulse generator for large-scale superconducting quantum computing
a Circuit diagram used for superimposing two microwave pulse generators. b By altering the initial value of the flux step, thus the phase of the microwave pulse for one of the signal sources, the photon number of the superimposed output can be periodically tuned between a constructive interference and a destructive interference, as indicated by the dashed gray lines. Those upper and lower limits are inferred based on the respective output photon number from the two devices and the temporal mode mismatch between the pulses. c The phase of the superimposed signal can also be tuned while keeping the output energy at the maximum. This is realized by using suitable combinations of the initial fluxes for the two signal sources to constructively superimpose the two pulses with the given phase. d Time series of a continuous-wave (CW) microwave signal, which is prepared by using a train of δ function-like magnetic flux pulses to operate the microwave source. e The frequency spectrum of a typical CW emission is a frequency comb. The frequency spacing of the comb can be tuned by the interval of the applied flux pulses δt. The dashed line is given by n/δt, where n is an integer. The power spectral densities have been normalized and offset for comparison purposes. f A typical linewidth of the CW emission measured with a spectrum analyzer, showing a resolution-limited linewidth below 1 Hz. Details about the linewidth estimation can be found in “Methods” section and Supplementary Fig. 9.
