Sub-Shot-Noise Transmission Measurement Enabled by Active Feed-Forward of Heralded Single Photons

Abstract

The limit of precision in optical measurements is due to quantum fluctuations, which are governed by Poissonian statistics. With a clever setup, however, the authors achieve a precision in transmission measurements that beats this limit, without the selective analysis of recorded data (post-selection). This shows that the single-photon-detector approach, used by many groups worldwide, is viable for real-world optical quantum metrology, not just proof-of-principle tests. In turn, this demonstration unlocks an array of techniques for quantum-state engineering that crucially depend on single-photon detection.