A high-gain and high-fidelity coherent state comparison amplifier

Ross J Donaldson,John Jeffers,Robert J Collins,Luca Mazzarella,Gerald S Buller

doi:10.1038/s42005-018-0054-z

Ross J Donaldson, John Jeffers + Show 3 more

Open Access

https://doi.org/10.1038/s42005-018-0054-z

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Abstract

Optical signals are subject to a distance-dependent loss as they propagate through transmission media. High-intensity, classical, optical signals can routinely be amplified to overcome the degradation caused by this loss. However, quantum optical states cannot be deterministically amplified and any attempt to do so will introduce intrinsic noise that spoils the desired quantum properties. Non-deterministic optical amplification, based on post-selection of the output depending on certain conditioning detection outcomes, is an emerging enabling technology in quantum measurement and quantum communications. Here we present an investigation into the properties of a simple, modular optical state comparison amplifier operating on weak coherent states. This amplifier requires no complex quantum resources and is based on linear optical components allowing for a high amplification rate at high gain and fidelity. We examine the amplifier’s performance in different configurations and develop an accurate analytical model that accounts for typical experimental scenarios.

Highlights

Optical signals are subject to a distance-dependent loss as they propagate through transmission media
The potential vulnerabilities of widely employed public-key encryption systems[1] have led to the development of alternative communications protocols, such as quantum key distribution (QKD)[2,3] and quantum digital signatures[4,5], that employ the laws of quantum mechanics and can, with the correct implementation, achieve unconditional security[6]
Results from the enhanced gain state comparison amplifier (SCAMP) configuration using only a single subtraction stage are presented first to establish the base characteristics of the amplifier

Summary

Introduction

Optical signals are subject to a distance-dependent loss as they propagate through transmission media. We present an investigation into the properties of a simple, modular optical state comparison amplifier operating on weak coherent states This amplifier requires no complex quantum resources and is based on linear optical components allowing for a high amplification rate at high gain and fidelity. An attempt to amplify these weak coherent states using deterministic methods introduces noise that destroys any quantum properties of the signal[11,12]. We consider the comparatively simple state comparison amplifier (SCAMP)[34] Operation of this amplifier requires only coherent state sources (such as an attenuated laser), linear-optical components (primarily beamsplitters and phase modulators), and single-photon avalanche diode (SPAD) detectors operating in Geiger-mode[35], making the SCAMP approach considerably easier to implement than other proposed schemes for quantum amplification. We have demonstrated increased output fidelity, at some cost to the gain, by introducing a second subtraction stage

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