20 Mai – Thesis defense - Xinhao Zou
13 h Amphi - Institut d’Optique d’Aquitaine (Talence)
Atom gradiometry for future gravitational wave detectors.
Gravitational waves expand our observation scope of the universe, carrying information through time and space undisturbed due to their inability to be scattered or absorbed. The detection of gravitational waves is of great significance to the progress of fundamental physics research and associated experimental technology. Gravitational-wave observatories are in operation or under construction worldwide, with detection frequencies ranging from 10^-9 Hz to 10^4 Hz.
The Matter Wave Interferometer Gravitational Antenna (MIGA) experiment aims to build an atomic gradiometer consisting of one 150 m long optical cavities on the LSBB platform based on the increasingly mature atomic interference technology. Compared with optical interferometers, atom gradiometers can reduce noise in the low-frequency range, filling a gap in gravitational wave detection in the band 0.1 Hz - 10 Hz.
At LP2N, as a demonstration experiment for gravitational wave antennas, an atom interferometer based on quasi-Bragg scattering and marginally-stable cavity has been built. We are currently building a 6.35 m atom gradiometer composed of two atom sources and made the first attempt to observe an interference signal. We discuss the implementation of this atom gradiometer, focusing on our achieved vacuum of 1.4x10^-9 mbar in an enormous vacuum chamber as well as the completed tuning of the first atomic source.
This thesis elucidates the difference between an atom gradiometer and an optical interferometer for gravitational wave detection. We propose a nested three-cavity system through two orthogonal optical cavities - a structure that can improve the strain sensitivity of atom interferometry, allowing it to exceed the standard quantum limit.