Neutron displacement noise-free interferometer for gravitational-wave detection

TL;DR

This paper proposes a neutron-based displacement noise-free interferometer (DFI) that can detect gravitational waves at lower frequencies than laser DFIs, potentially opening new observational windows for astrophysics.

Contribution

The paper introduces a novel neutron DFI design that extends the sensitive frequency band to lower frequencies, overcoming limitations of laser DFIs.

Findings

Neutron DFI can operate effectively at ~0.1 Hz frequency band.

Neutron DFI can detect gravitational waves inaccessible to laser interferometers.

The design leverages the lower velocity of neutrons to reduce noise sensitivity.

Abstract

An interferometer design that cancels all displacement noises of its test masses and maintains a gravitational-wave (GW) signal by combining multiple detector signals is called a displacement noise-free interferometer (DFI). The idea has been considered previously for a laser interferometer. However, a limitation of a laser DFI is that its sensitive frequency band is too high for astrophysical GW sources, $\sim 10^5\,{\rm Hz}$ even for a kilometer-sized interferometer. To circumvent this limitation, in this paper, we propose a neutron DFI, in which neutrons are used instead of light. Since neutrons have velocities much lower than the speed of light, the sensitive frequency band of a neutron DFI can be lowered down to $\sim 10^{-1}\,{\rm Hz}$. Therefore, a neutron DFI can be utilized for detecting GWs that are inaccessible by an ordinary laser interferometer on the ground.