A tunable High-Q millimeter wave cavity for hybrid circuit and cavity QED experiments

TL;DR

This paper presents a high-Q millimeter wave cavity with tunability and strong coupling capabilities, enabling advanced quantum experiments involving Rydberg atoms at around 100 GHz.

Contribution

The authors introduce a novel 3D mm-wave cavity with record high quality factor, in-situ tunability, and optical accessibility for hybrid quantum systems.

Findings

Achieved a single-photon internal quality factor of 3×10^7 at 98.2 GHz.

Demonstrated in-situ piezo tunability of 18 MHz.

Enabled hybrid mm-wave and optical cavity for quantum interconversion.

Abstract

The millimeter wave (mm-wave) frequency band provides exciting prospects for quantum science and devices, since many high-fidelity quantum emitters, including Rydberg atoms, molecules and silicon vacancies, exhibit resonances near 100 GHz. High-Q resonators at these frequencies would give access to strong interactions between emitters and single photons, leading to rich and unexplored quantum phenomena at temperatures above 1K. We report a 3D mm-wave cavity with a measured single-photon internal quality factor of $3 \times 10^{7}$ and mode volume of $0.14 \times \lambda^3$ at $98.2$ GHz, sufficient to reach strong coupling in a Rydberg cavity QED system. An in-situ piezo tunability of $18$ MHz facilitates coupling to specific atomic transitions. Our unique, seamless and optically accessible resonator design is enabled by the realization that intersections of 3D waveguides support tightly confined bound states below the waveguide cutoff frequency. Harnessing the features of our cavity design, we realize a hybrid mm-wave and optical cavity, designed for interconversion and entanglement of mm-wave and optical photons using Rydberg atoms.