Demonstration of reversible phase-insensitive optical amplifier

Abstract

We experimentally demonstrate phase-insensitive linear optical amplification which preserves the idler at the output. Since our amplification operation is unitary up to small excess noise, it is reversible beyond the classical limit. The entanglement between the two output modes is the resource for the reversibility. The amplification gain of 2.0 is demonstrated. In addition, combining this amplifier with a beamsplitter, we also demonstrate approximate cloning of coherent states where an anticlone is present. We investigate the reversibility by reconstructing the initial state from the output correlations, and the results are slightly beyond the cloning limit. Furthermore, full characterization of the amplifier and cloner is given by using coherent states with several different mean values as inputs. Our amplifier is based on linear optics, offline preparation of nonclassical ancillas, and homodyne measurements followed by feedforward. Squeezed states are used as the ancillas, and nonlinear optical effects are exploited only for their generation. The ancillas introduce nonclassicality into the amplifying operation, making entanglement at the output.

16 pages, 17 figures

References in corpus (7)

• Continuous-variable quantum cryptography is secure against non-gaussian attacks
• The optimal cloning of quantum coherent states is non-Gaussian
• Demonstration of a quantum nondemolition sum gate
• Demonstration of deterministic and high fidelity squeezing of quantum information
• 7 dB quadrature squeezing at 860 nm with periodically-poled KTiOPO4
• Universal optical amplification without nonlinearity
• Optimal multicopy asymmetric Gaussian cloning of coherent states