Conventional heterodyne readout schemes are now under reconsideration due to the realization of techniques to evade its inherent 3 dB signal-to-noise penalty. The application of high-frequency, spectrally entangled, two-mode squeezed states can further improve the readout sensitivity of audio-band signals. In this paper, we experimentally demonstrate quantum-enhanced heterodyne readout of two spatially distinct interferometers with direct optical signal combination, circumventing the 3 dB heterodyne signal-to-noise penalty. Applying a high-frequency, spectrally entangled, two-mode squeezed state, we show further signal-to-noise improvement of an injected audio band signal of 3.5 dB. This technique is applicable for quantum-limited high-precision experiments, with application to searches for quantum gravity, gravitational wave detection and wavelength-multiplexed quantum communication.
@article{arxiv.2401.04940,
title = {Quantum enhanced balanced heterodyne readout for differential interferometry},
author = {Daniel W. Gould and Vaishali B. Adya and Sheon S. Y. Chua and Jonas Junker and Dennis Wilken and Terry G. McRae and Bram J. J. Slagmolen and Min Jet Yap and Robert L. Ward and Michèle Heurs and David E. McClelland},
journal= {arXiv preprint arXiv:2401.04940},
year = {2024}
}