Researchers at the Institute of Nanoscience of the National Research Council of Italy (Cnr Nano) have demonstrated a compact superconducting device capable of generating coherent microwave frequency combs, extending a key metrological tool from the optical to the microwave domain. The work, published in Nature Communications, opens new perspectives for on-chip signal generation in quantum technologies, sensing and precision measurements.
Frequency combs are widely used in optics as ultra-precise references for measuring time and frequency, thanks to their evenly spaced and phase-coherent spectral lines. By transferring this concept to lower frequencies, the team, led by Alessandro Crippa together with Francesco Giazotto, Angelo Greco, and Xavier Ballu, has developed a platform that operates directly in the microwave range, which is central to superconducting and semiconductor-based quantum devices.
The researchers achieved this result using a micrometer-scale superconducting quantum interference device (SQUID), exploiting the AC Josephson effect to generate a train of voltage pulses. In the frequency domain, these pulses correspond to a comb structure with dozens of coherent modes, experimentally observed up to the 46th harmonic within the 4–8 GHz bandwidth.
“Our key result is that a superconducting SQUID only a few micrometers in size can generate a highly stable and coherent set of microwave tones,” explains Alessandro Crippa. “Instead of producing a single frequency, the device emits a full comb of evenly spaced signals, with extremely low power consumption and a footprint compatible with on-chip integration.”
Unlike conventional approaches, the device does not rely on bulky resonant structures and dissipates negligible power (−170 to −130 dBm per harmonic), making it particularly suitable for cryogenic environments. This is a crucial advantage for quantum technologies, where external signals are typically difficult to deliver without introducing noise and thermal load.
“For quantum systems operating close to absolute zero, bringing signals from room temperature is a major challenge,” adds Francesco Giazotto. “Generating them directly on chip can significantly reduce noise and heat, enabling more efficient and scalable architectures.”
Beyond quantum computing, microwave frequency combs could enable new strategies for high-precision spectroscopy, signal synchronization and radioastronomy. “More broadly, the work demonstrates how concepts originally developed in optical physics can be translated into solid-state superconducting platforms, paving the way for hybrid approaches to quantum control”, adds Crippa.
The device builds on an idea originally conceived over a decade ago and was realized through the combined efforts of Angelo Greco, Xavier Ballu and colleagues at the NEST laboratory of Cnr Nano and the Scuola Normale Superiore.
Future developments will focus on optimizing materials and geometries to enhance emission power and extend operation to higher temperatures, with the long-term goal of transferring the full potential of optical frequency comb techniques to the microwave regime.
Reference article [freely available in Open Access]: Coherent microwave comb generation via the Josephson effect. Angelo Greco, Xavier Ballu, Francesco Giazotto, and Alessandro Crippa. Nat Commun 17, 2972 (2026). https://doi.org/10.1038/s41467-026-69652-1
[IMAGE: Electron microscope image of the device: in yellow, the waveguide through which the current flows; in blue, the superconducting SQUID, with Josephson junctions (red circles) that generate the pulses of the frequency comb]
