Demonstrating an absolute quantum advantage in direct absorption measurement

Paul-Antoine Moreau, Javier Sabines Chesterking, Beccie Solweling Whittaker, Siddarth Joshi, Patrick Birchall, Alex McMillan, John Rarity, Jonathan Matthews

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

45 Citations (Scopus)
392 Downloads (Pure)


Engineering apparatus that harness quantum theory promises to offer practical advantages over current technology. A fundamentally more powerful prospect is that such quantum technologies could out-perform any future iteration of their classical counterparts, no matter how well the attributes of those classical strategies can be improved. Here, for optical direct absorption measurement, we experimentally demonstrate such an instance of an absolute advantage per photon probe that is exposed to the absorbative sample. We use correlated intensity measurements of spontaneous parametric downconversion using a commercially available air-cooled CCD, a new estimator for data analysis and a high heralding efficiency photon-pair source. We show this enables improvement in the precision of measurement, per photon probe, beyond what is achievable with an ideal coherent state (a perfect laser) detected with 100% efficient and noiseless detection. We see this absolute improvement for up to 50% absorption, with a maximum observed factor of improvement of 1.46. This equates to around 32% reduction in the total number of photons traversing an optical sample, compared to any future direct optical absorption measurement using classical light.
Original languageEnglish
Article number6256
Number of pages7
JournalScientific Reports
Publication statusPublished - 24 Jul 2017

Structured keywords

  • Bristol Quantum Information Institute
  • QETLabs

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