Noise-powered probabilistic concentration of phase information

• Published in: Nature physics Vol. 6; no. 10; pp. 767 - 771
• Main Authors: Usuga, Mario A, Müller, Christian R, Andersen, Ulrik L, Wittmann, Christoffer, Marek, Petr, Filip, Radim, Marquardt, Christoph, Leuchs, Gerd
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2010; Nature Publishing Group
• Subjects: Amplification; Amplifiers; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Experiments; letter; Mathematical and Computational Physics; Metrology; Molecular; Noise; Optical and Plasma Physics; Optics; Physics; Physics and Astronomy; Probabilistic methods; Probability; Probability theory; Quantum amplifiers; Quantum physics; Theoretical; Uncertainty
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1743

Phase-insensitive optical amplification of an unknown quantum state is known to be a fundamentally noisy operation that inevitably adds noise to the amplified state. 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 scheme. 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.