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

Javier Sabines Chesterking, Hugo Cable, Jeremy O'Brien, John Rarity, Paul-Antoine Moreau, Patrick Birchall, Jonathan Matthews, Rebecca Whittaker, Siddarth Joshi, Alex McMillan

Research output: Contribution to journalArticle (Academic Journal)peer-review

21 Citations (Scopus)
421 Downloads (Pure)


Harnessing the unique properties of quantum mechanics offers the possibility of delivering alternative technologies that can fundamentally outperform their classical counterparts. These technologies deliver advantages only when components operate with performance beyond specific thresholds. For optical quantum metrology, the biggest challenge that impacts on performance thresholds is optical loss. Here, we demonstrate how including an optical delay and an optical switch in a feed-forward configuration with a stable and efficient correlated photon-pair source reduces the detector efficiency required to enable quantum-enhanced sensing down to the detection level of single photons and without postselection. When the switch is active, we observe a factor of improvement in precision of 1.27 for transmission measurement on a per-input-photon basis compared to the performance of a laser emitting an ideal coherent state and measured with the same detection efficiency as our setup. When the switch is inoperative, we observe no quantum advantage.
Original languageEnglish
Article number014016
Number of pages6
JournalPhysical Review Applied
Publication statusPublished - 17 Jul 2017

Structured keywords

  • Bristol Quantum Information Institute
  • QETLabs


  • Quantum Metrology
  • Quantum optics

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