Entanglement-enhanced measurement of a completely unknown optical phase
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Precise interferometric measurement is vital to many scientific and technological applications. Using quantum entanglement allows interferometric sensitivity that surpasses the shot-noise limit (SNL)1, 2. To date, experiments demonstrating entanglement-enhanced sub-SNL interferometry3, 4, 5, 6, and most theoretical treatments7, 8, 9, 10, 11, 12, 13, have addressed the goal of increasing signal-to-noise ratios. This is suitable for phase-sensing-detecting small variations about an already known phase. However, it is not sufficient for ab initio phase-estimation-making a self-contained determination of a phase that is initially completely unknown within the interval [0, 2p). Both tasks are important2, but not equivalent. To move from the sensing regime to the ab initio estimation regime requires a non-trivial phase-estimation algorithm14, 15, 16, 17. Here, we implement a 'bottom-up' approach, optimally utilizing the available entangled photon states, obtained by post-selection5, 6. This enables us to demonstrate sub-SNL ab initio estimation of an unknown phase by entanglement-enhanced optical interferometry.
Copyright 2010 Nature Publishing Group. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal website for access to the definitive, published version.
Optical Physics not elsewhere classified