USTC Proposes Higher Precision Quantum Metrology

  • [2016-12-02]

    Prof. LI Chuanfeng, Dr. TANG Jianshun and their collaborators experimentally demonstrate higher precision weak-value-based metrology with power recycling. Their results show that the detected signal can be strengthened by power recycling, and the power-recycled weak-value-based signal-to-noise ratio can surpass the upper limit of the classical scheme, corresponding to the shot-noise limit. This work sheds light on higher precision metrology and explores the real advantage of the weak-value-based metrology over classical metrology. This work is published in Physical Review Letters on December 2nd.

    Weak-value-based metrology has shown its great power in signal amplification since it was first introduced by Aharonov, Albert, and Vaidman in 1988. To date, this weak-value-amplification technique has been successfully employed in the measurement of some small physical effects. However, in the technical-noise-free situation, considering the trade-off relation between the amplification effect and the probe loss induced by the postselection in this protocol, a direct question is raised of whether the weak-value-amplification technique can improve the ultimate limit of the measurement precision, i.e., to go beyond the signal-to-noise ratio.

    Nevertheless, a recent proposal shows that this probe loss can be reduced by the power-recycling technique, and thus enhance the precision of weak-value-based metrology. Prof. Li’s group experimentally realizes the power-recycled interferometric weak-value-based beam-deflection measurement and obtains the amplitude of the detected signal and white noise (dominated by shot noise) by discrete Fourier transform. Their results show that the detected signal (proportional to the beam deflection) is amplified by a gain factor of 2.4 in the power-recycled weak value measurement compared to the standard weak value scheme. Moreover, the signal-to-noise ration related to the white noise in the power-recycled weak value measurement indeed surpasses the signal-to-noise ration limit of the standard weak value and classical schemes. These results indicate that the weak value amplification metrology shows an obvious measurement-precision advantage over the classical metrology when the power-recycling technique is combined.


    Fig. 1 The schematic diagram of three metrological protocols: the classical metrology, standard weak value metrology and power recycled weak value metrology (Image file from Physical Review Letters)


    Fig. 2 The signal-to-noise ration of the three metrological protocols (Image file from Physical Review Letters)

    This work is supported from Ministry of Science and Technology of China, National Natural Science Foundation of China, The Chinese Academy of Sciences and Synergetic Innovation Center of Quantum Information and Quantum Physics.

    Contact: Prof. LI Chuan-Feng


    paper Link:


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