A detector of small harmonic displacements based on two coupled microwave cavities

TL;DR

This paper presents a highly sensitive detector for small harmonic displacements using coupled superconducting microwave cavities, improving previous sensitivity levels and discussing potential applications in gravitational wave detection.

Contribution

It introduces an improved experimental setup for a microwave cavity-based displacement detector, achieving greater sensitivity and outlining future development directions for gravitational wave detection.

Findings

Achieved sensitivity of dl/l~10^{-20} Hz^{-1/2}

Repeated and improved upon previous experiments from 1984

Discussed potential for gravitational wave detection

Abstract

The design and test of a detector of small harmonic displacements is presented. The detector is based on the principle of the parametric conversion of power between the resonant modes of two superconducting coupled microwave cavities. The work is based on the original ideas of Bernard, Pegoraro, Picasso and Radicati, who, in 1978, suggested that superconducting coupled cavities could be used as sensitive detectors of gravitational waves, and on the work of Reece, Reiner and Melissinos, who, {in 1984}, built a detector of this kind. They showed that an harmonic modulation of the cavity length l produced an energy transfer between two modes of the cavity, provided that the frequency of the modulation was equal to the frequency difference of the two modes. They achieved a sensitivity to fractional deformations of dl/l~10^{-17} Hz^{-1/2}. We repeated the Reece, Reiner and Melissinos experiment, and with an improved experimental configuration and better cavity quality, increased the sensitivity to dl/l~10^{-20} Hz^{-1/2}. In this paper the basic principles of the device are discussed and the experimental technique is explained in detail. Possible future developments, aiming at gravitational waves detection, are also outlined.