Fig. 2: A coherent microwave pulse generator.
From: A cryogenic on-chip microwave pulse generator for large-scale superconducting quantum computing
a Pendulum oscillation induced by abruptly shifting the suspension point. During the sufficiently fast move, the pendulum globe almost keeps still. However, it is no longer at the equilibrium position of the modified pendulum, thus oscillation occurs thereafter. b Circuit diagram of the cryogenic microwave pulse generator, composing a λ/2 coplanar waveguide (CPW) resonator with a superconducting quantum interference device (SQUID) embedded in the middle of the center conductor. A flux line is used to control magnetic flux across the SQUID, and thus operate the pulse generator. c The measured resonance frequency of the resonator shows a periodic dependence on the magnetic flux across the SQUID, which can be well-fitted with a theoretical curve (orange lines)23,24. As illustrated by the arrowed lines, by applying a fast change of magnetic flux across the ϕ = (n + 1/2)ϕ0 point (gray dashed lines), where n is an integer and ϕ0 is the flux quantum, microwave pulses can be generated in the resonator and released to the measurement setup. d The emitted microwave pulse has an exponential decay envelope (orange line) with a time constant determined by the linewidth of the resonator. The inset of d is a zoom-in of the time series, which can be well-fitted with an exponential-enveloped sinusoidal function (red line), exhibiting well-defined coherence. e Output photon number from the pulse generator driven with a varied initial flux, showing that the flux change across at least one (n + 1/2)ϕ0 point is necessary to generate microwave pulse. f–h the phase, photon number, and frequency of the microwave pulse can be well controlled by tuning the starting flux, slope, and ending flux of the flux steps used to operate the pulse generator, correspondingly. The insets of e–h illustrate the applied magnetic flux steps.
