Coherent microwave comb generation by Josephson effect

Integration and scaling up of superconducting quantum computers is a serious challenge that requires efforts at more levels to be achieved.
To this end we present a novel device for generating frequency combs in the microwave regime based on a superconducting quantum interference device (SQUID) driven by a time-dependent magnetic flux. The flux drive induces sharp periodic voltage spikes across the SQUID, which in the frequency domain correspond to an evenly spaced comb centered in 0 Hz.
The emitted frequency comb extends in the range 4-8 GHz, showing a hundreds of harmonics. It is fully tunable in amplitude and inter-teeth spacing by adjusting the flux modulation frequency, amplitude and offset.
The produced radiation exhibits long coherence times, extending up to several seconds for the single mode. We also show a well defined constant phase relation among the comb teeth.
Having a small footprint (<100 um), our approach provides a compact solution for generating coherent microwave tones in cryogenic environments, addressing frequency crowding issues in superconducting circuit architectures. The demonstrated device has potential applications in cryogenic microwave electronics, quantum computing, and metrology, paving the way for new techniques in frequency synthesis and signal processing in low-temperature environments.