A high quality, efficiently coupled microwave cavity for trapping cold molecules

TL;DR

This paper presents a detailed characterization and theoretical modeling of a compact Fabry-Perot microwave cavity optimized for trapping cold molecules, focusing on coupling efficiency, quality factor, and mode profile.

Contribution

It introduces a comprehensive analytical model and experimental validation for a microwave cavity with optimized coupling and minimal diffraction losses.

Findings

Optimal hole size for maximum intra-cavity electric field

Quality factor decreases slightly with larger coupling holes

Good agreement between measurements, theory, and simulations

Abstract

We characterize a Fabry-Perot microwave cavity designed for trapping atoms and molecules at the antinode of a microwave field. The cavity is fed from a waveguide through a small coupling hole. Focussing on the compact resonant modes of the cavity, we measure how the electric field profile, the cavity quality factor, and the coupling efficiency, depend on the radius of the coupling hole. We measure how the quality factor depends on the temperature of the mirrors in the range from 77 to 293K. The presence of the coupling hole slightly changes the profile of the mode, leading to increased diffraction losses around the edges of the mirrors and a small reduction in quality factor. We find the hole size that maximizes the intra-cavity electric field. We develop an analytical theory of the aperture-coupled cavity that agrees well with our measurements, with small deviations due to enhanced diffraction losses. We find excellent agreement between our measurements and finite-difference time-domain simulations of the cavity.