Gravitational wave spectrometry with a Hong–Ou–Mandel interferometer in space

The possibility to use a Hong–Ou–Mandel (HOM) interferometer to carry out gravitational waves detection and spectrometry is investigated. The noise budget of the instrument is evaluated. The basic experimental requirements are calculated. It is shown that the power and wavelength of the heralded photon source, together with the angular accuracy of the measurement of the photon polarization rotation, form the main constraints to determine the type of gravitational waves sources, which would be the target of HOM gravitational wave spectrometers. The currently available pW power heralded photon sources, with typical heralded photon frequencies in the order of 10¹⁴ Hz (visible—UV part of the optical spectrum) are totally unsuitable, in terms of required detection time for any of the GW sources, which are presently targeted by ground and space based GW detectors. The operation of the HOM interferometer as a GW spectrometer is illustrated with a numerical model that uses the gravitational wave strain data recorded by LIGO on 14 September 2015 (GW150914 event). Assuming an angular accuracy of rad for the measurement of photons polarization rotation, these measurements could only be carried out with HOM interferometer's arm lengths of the order of 10.000 km (only achievable in space, if we do not use optical cavities), and by using heralded photon sources of about 1 W power, producing heralded photons with wavelengths in the radio-wave band of the electromagnetic spectrum, 10 MHz. Although the technology to produce this type of heralded photon sources is currently not available, a brief discussion of the possible implementation of a large arm HOM interferometer in space is introduced. (paper)