# Coherent microwave comb generation via the Josephson effect

## TL;DR

Researchers created a compact, low-energy microwave frequency comb using a superconducting device, which could advance quantum technologies.

## Contribution

A novel on-chip microwave comb generator using the ac Josephson effect in a superconducting quantum interference device.

## Key findings

- The comb emits up to mode 46 with a dynamic range of 40 dB in the 4-8 GHz bandwidth.
- The device operates at 60 mK with a micrometer-scale footprint and minimal dissipation.

## Abstract

Frequency combs represent exceptionally precise measurement tools due to the coherence of their spectral lines. While optical frequency comb sources constitute a well-established technology, superconducting circuits provide a relatively unexplored on-chip platform for low-dissipation comb emitters able to span from gigahertz to terahertz frequencies. We demonstrate coherent microwave frequency comb generation by leveraging the ac Josephson effect in a superconducting quantum interference device. A time-dependent magnetic drive periodically generates voltage pulses, which in the frequency domain correspond to a comb with dozens of spectral modes here reported up to mode 46. The emitted power at the device level ranges from −170 dBm to −130 dBm per harmonic, corresponding to 40 dB dynamic range in the 4-8 GHz bandwidth. The micrometer-scale footprint and minimal dissipation inherent to superconducting systems foster the integration of our comb generator with advanced cryogenic electronics. Transferring optical techniques to the solid-state domain may enable new applications in quantum technologies.

The authors demonstrate the use of a superconducting quantum interference device with time dependent magnetic drive as a source for coherent frequency combs in the microwave C-band (4-8 GHz), operating at 60 mK. The device has μm-size physical footprint, extremely low dissipation, and large bandwidth.