Phase-Sensitive Light Amplifiers in Stellar Interferometry

N. R. Brewer, Tian Li, K. M. Jones +1 more

V.N. Melekhin, S. A. Mishin

Wei Du, Shidong Bao, Peiyu Yang +5 more

Correlated interferometry offers various advantages in precision measurements, such as sub-shot noise sensitivity, high resolution, and prevention of detector saturation benefiting from dark output. In certain practical scenarios, e.g. absorptive measurement, there is usually unbalanced loss between the probe and reference beams, which destroys the correlation and remains a significant obstacle in the efficient application of entanglements. Here, we study the performance of a nonlinear interferometer whose arms experience unbalanced loss and demonstrate the use of a phase-sensitive amplifier in the sensing or reference arms to amplify or squeeze the light field, which can both reduce the degradation of quantum enhancement from unbalanced absorption in a lossy environment. We find that the loss after amplification, i.e. from imperfect interferometry and detection, can be mitigated when the phase-sensitive amplifier is placed at the sensing arm and functions as a noiseless amplifier. Our approach may be helpful to the practical application of quantum-enhanced absorptive measurement.

Pierre Riaud

Maria V. Chekhova, Gaetano Frascella, Sascha Agne +1 more

An important part of optical sensing is interferometry, where direct or homodyne detection at the output of an interferometer yields information about small phase shifts. Classical interferometry operates at the shot-noise limit (SNL), caused by the photon structure of light and reached when an interferometer is fed with coherent light. The use of nonclassical light at the input of an interferometer enables overcoming the SNL. In particular, squeezed light is known to be less noisy than coherent light. An interferometer fed with strongly squeezed light can, in principle, provide the phase sensitivity at the Heisenberg limit, the ultimate limit allowed by the laws of physics. However, this supersensitive operation is strongly degraded by loss – both inside the interferometer and outside it, at the stage of detection. While the former (internal loss) seems to be inevitable, the latter (detection loss) can be overcome, and we demonstrate it in our recent experiment. The clue is to amplify light at the interferometer output using a phase-sensitive optical parametric amplifier. This device does not introduce additional noise, but it amplifies the fragile quantum signal and thus makes it tolerant to loss at the detection stage. In a proof-of-principle experiment, we build a polarization Mach-Zehnder interferometer and feed it with coherent light in one port and a squeezed vacuum in another port. At one output port, we amplify light with an optical parametric amplifier and measure a phase sensitivity of 13 mrad for 1500 photons in the interferometer. This result, achieved with 50% detection efficiency, overcomes the SNL by 3 dB. Moreover, by using stronger amplification, we can overcome the SNL under detection efficiency as low as 13%. Our results outline a way to use squeezed light for real-life sensing, where the detection efficiency cannot be very high, especially in spectral ranges like middle-infrared or terahertz.

Andreas Wicht, M. Müller, Volker Quetschke +3 more