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  • Unconditional violation of ...
    Slussarenko, Sergei; Weston, Morgan M.; Chrzanowski, Helen M.; Shalm, Lynden K.; Verma, Varun B.; Nam, Sae Woo; Pryde, Geoff J.

    Nature photonics, 11/2017, Letnik: 11, Številka: 11
    Journal Article

    (ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Interferometric phase measurement is widely used to precisely determine quantities such as length, speed and material properties 1 – 3 . Without quantum correlations, the best phase sensitivity ... achievable using n photons is the shot-noise limit, ... Quantum-enhanced metrology promises better sensitivity, but, despite theoretical proposals stretching back decades 3 , 4 , no measurement using photonic (that is, definite photon number) quantum states has truly surpassed the shot-noise limit. Instead, all such demonstrations, by discounting photon loss, detector inefficiency or other imperfections, have considered only a subset of the photons used. Here, we use an ultrahigh-efficiency photon source and detectors to perform unconditional entanglement-enhanced photonic interferometry. Sampling a birefringent phase shift, we demonstrate precision beyond the shot-noise limit without artificially correcting our results for loss and imperfections. Our results enable quantum-enhanced phase measurements at low photon flux and open the door to the next generation of optical quantum metrology advances. Unconditional entanglement-enhanced photonic interferometry is implemented by using a state-of-the-art photon source and detectors. Sampling a birefringent phase shift, precision beyond the shot-noise limit is demonstrated without data correction.