Experimental Implementation of a Quantum Optical State Comparison Amplifier

Abstract

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.

Experimental noiseless linear amplification using weak measurements

“…In principle, a weak measurement based approach can provide optimal performance in the low gain limit [14] and provides a general framework for realising heralded amplifiers as deterministic entangling operations for optical systems begin to be realised. An interesting alternative strategy for amplifying quantum states has been demonstrated [25] in which the probability of successful operation can be improved, a caveat is that the amplifier operates only for a limited alphabet of states.…”

From retrodiction to Bayesian quantum imaging

“…It has been valuable, however, in simplifying calculations and, more importantly, suggesting possibilities and ideas that are not readily apparent in the more familiar predictive approach. Striking examples include a novel class of generalised measurements [24,25], quantum information processing in the past [26] and the quantum scissors device [27,28] and the field of noiseless amplification that it led to [29][30][31][32][33]. In the context of quantum imaging, it has provided a novel analysis of entangled photon ghost imaging [34] including a justification for the Klyshko interpretation of the phenomenon [35].…”

Models of reduced-noise, probabilistic linear amplifiers

“…Ralph and Lund [6] and, independently, Fiurášek [7] (in the context of cloning) proposed an intriguing idea that suggested it might be possible to build an amplifier that subtracts noise! This proposal continues to generate interest from the community [8][9][10][11][12][13][14][15][16][17], with potential applications including quantum key distribution [18][19][20] and the distillation of quantum correlations [12]. Specifically, the proposed amplifier with amplitude gain g > 1 takes an input coherent state |α to a "target" coherent state |gα with (success) probability p and fails with probability 1 − p .…”