Abstract
Phase-insensitive optical amplification of an unknown quantum state is known to be a fundamentally noisy operation that inevitably adds noise to the amplified state1,2,3,4,5. However, this fundamental noise penalty in amplification can be circumvented by resorting to a probabilistic scheme as recently proposed and demonstrated in refs 6, 7, 8. These amplifiers are based on highly non-classical resources in a complex interferometer. Here we demonstrate a probabilistic quantum amplifier beating the fundamental quantum limit using a thermal-noise source and a photon-number-subtraction scheme9. The experiment shows, surprisingly, that the addition of incoherent noise leads to a noiselessly amplified output state with a phase uncertainty below the uncertainty of the state before amplification. This amplifier might become a valuable quantum tool in future quantum metrological schemes and quantum communication protocols.
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Acknowledgements
This work was supported by the EU project COMPAS, the BIOP Graduate school, the Lundbeck foundation and the DFG project LE 408/19-1. R.F. and P.M. acknowledge support from projects No. MSM 6198959213 and No. LC06007 of the Czech Ministry of Education, the Grant 202/08/0224 of GA CR and the Alexander von Humboldt Foundation. P.M. acknowledges support from the Grant P205/10/P319 of GA CR.
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M.A.U., C.R.M. and C.W. carried out the experimental work, P.M. and R.F. did the theoretical calculations and all authors discussed the results. U.L.A., M.A.U. and C.R.M. wrote the manuscript and Ch.M., G.L. and U.L.A. coordinated the project.
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Usuga, M., Müller, C., Wittmann, C. et al. Noise-powered probabilistic concentration of phase information. Nature Phys 6, 767–771 (2010). https://doi.org/10.1038/nphys1743
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DOI: https://doi.org/10.1038/nphys1743
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