Experimental implementation of a quantum optical state comparison amplifier

Donaldson, Ross J. and Collins, Robert J. and Eleftheriadou, Electra and Barnett, Stephen M. and Jeffers, John and Buller, Gerald S. (2015) Experimental implementation of a quantum optical state comparison amplifier. Physical Review Letters, 114 (12). 120505. ISSN 0031-9007

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    We present an experimental demonstration of a practical nondeterministic quantum optical amplification scheme that employs two mature technologies, state comparison and photon subtraction, to achieve amplification of known sets of coherent states with high fidelity. The amplifier uses coherent states as a resource rather than single photons, which allows for a relatively simple light source, such as a diode laser, providing an increased rate of amplification. The amplifier is not restricted to low amplitude states. With respect to the two key parameters, fidelity and the amplified state production rate, we demonstrate significant improvements over previous experimental implementations, without the requirement of complex photonic components. Such a system may form the basis of trusted quantum repeaters in nonentanglement-based quantum communications systems with known phase alphabets, such as quantum key distribution or quantum digital signatures.