Gould Daniel W, Adya Vaishali B, Chua Sheon S Y, Junker Jonas, Wilken Dennis, McRae Terry G, Slagmolen Bram J J, Yap Min Jet, Ward Robert L, Heurs Michèle, McClelland David E
OzGrav, Centre for Gravitational Astrophysics, Research School of Physics and Research School of Astronomy and Astrophysics, <a href="https://ror.org/019wvm592">Australian National University</a>, Australian Capital Territory, Australia.
Nonlinear and Quantum Photonics Lab, Department of Applied Physics, <a href="https://ror.org/026vcq606">KTH Royal Institute of Technology</a>, Stockholm, Sweden.
Phys Rev Lett. 2024 Aug 9;133(6):063602. doi: 10.1103/PhysRevLett.133.063602.
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, quadrature-entangled, two-mode squeezed states can further improve the readout sensitivity of audio-band signals. In this Letter, 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, quadrature-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, searches for dark matter, gravitational wave detection, and wavelength-multiplexed quantum communication.
