Detecting kHz gravitons from a neutron star merger with a multi-mode resonant mass detector

TL;DR

This paper proposes a multi-mode resonant mass detector designed to identify kHz gravitons from neutron star mergers by leveraging coupled normal modes and energy measurements, potentially enabling direct graviton counting.

Contribution

It introduces a novel multi-mode bar detector with coupled normal modes that enhances graviton detection sensitivity compared to traditional single-mode detectors.

Findings

Normal modes retain coupling strength to gravitational waves.

Effective mass of modes is comparable to smallest mass element.

Feasibility of counting individual gravitons through energy measurements.

Abstract

We propose a multi-mode bar consisting of mass elements of decreasing size for the implementation of a gravitational version of the photo-electric effect through the stimulated absorption of up to kHz gravitons from a binary neutron star merger and post-merger. We find that the multi-mode detector has normal modes that retain the coupling strength to the gravitational wave of the largest mass-element, while only having an effective mass comparable to the mass of the smallest element. This allows the normal modes to have graviton absorption rates due to the tonne-scale largest mass, while the single graviton absorption process in the normal mode could be resolved through energy measurements of a mass-element in-principle smaller than pico-gram scale. We argue the feasibility of directly counting gravito-phonons in the bar through energy measurements of the end mass. This improves the transduction of the single-graviton signal, enhancing the feasibility of detecting single gravitons.