Cryogenic microwave frequency combs based on quantum paraelectric superconducting resonators

TL;DR

This paper introduces an all-electrical, on-chip cryogenic microwave frequency comb using quantum paraelectric SrTiO3, enabling integration with quantum technologies and tunable frequency ranges.

Contribution

It demonstrates a novel, low-power, on-chip microwave frequency comb based on SrTiO3's Pockels-like effect in its quantum paraelectric phase, suitable for cryogenic quantum applications.

Findings

Achieved on-chip microwave frequency comb generation at cryogenic temperatures.

Controlled the comb's frequency range via electric field tuning of SrTiO3's dielectric constant.

Enabled ultra-miniature, integrated design compatible with quantum technologies.

Abstract

A frequency comb, known for its precision as an "optical ruler", features an evenly spaced spectral pattern. While these combs are vital in photonic quantum technologies, their microwave counterparts are now highly sought after for cryogenic quantum technologies, including semiconducting and superconducting qubits and quantum electrical metrology, which mainly operate in the microwave regime. However, microwave combs are still largely underexplored, and typically rely on complex, high-power optical systems incompatible with the low-power, cryogenic on-chip quantum technologies. In this manuscript, we present an all-electrical, on-chip, cryogenic microwave frequency comb on Strontium Titanate (SrTiO$_3$), exploiting its Pockels-like effect in its quantum paraelectric phase. Our device, utilizing a superconducting microwave cavity, generating the frequency comb via cavity phase modulation enabled by the field-induced effective $\chi(2)$ of SrTiO$_3$. The ability to continuously vary the dielectric constant of SrTiO$_3$ by the application of electric field, in its quantum paraelectric phase, makes it possible to control the comb's operating frequency range. The exceptionally high dielectric constant of SrTiO$_3$, > 20,000 in its quantum paraelectric state, enables an ultra-miniature design and on-chip integration with cryogenic quantum technologies.