Quantum enhancement of signal-to-noise ratio with a heralded linear amplifier

TL;DR

This paper introduces a novel heralded linear amplification scheme combining probabilistic and deterministic methods to enhance quantum signal-to-noise ratio, enabling improved quantum communication over longer distances.

Contribution

The authors develop a flexible linear amplification scheme that achieves signal amplification beyond classical limits using linear optics and post-selection, with tunable performance trade-offs.

Findings

Achieved a signal transfer coefficient greater than 1 without statistical distortion.

Demonstrated a maximum transfer coefficient of 2.55 ± 0.08.

Scheme relies solely on linear optics and post-selection, suitable for quantum networks.

Abstract

Due to the pervasive nature of decoherence, protection of quantum information during transmission is of critical importance for any quantum network. A linear amplifier that can enhance quantum signals stronger than their associated noise while preserving quantum coherence is therefore of great use. This seemingly unphysical amplifier property is achievable for a class of probabilistic amplifiers that does not work deterministically. Here we present a linear amplification scheme that realises this property for coherent states by combining a heralded measurement-based noiseless linear amplifier and a deterministic linear amplifier. The concatenation of two amplifiers introduces the flexibility that allows one to tune between the regimes of high-gain or high noise-reduction, and control the trade-off of these performances against a finite heralding probability. We demonstrate an amplification signal transfer coefficient of $\mathcal{T}_s > 1$ with no statistical distortion of the output state. By partially relaxing the demand of output Gaussianity, we can obtain further improvement to achieve a $\mathcal{T}_s = 2.55 \pm 0.08$. Our amplification scheme only relies on linear optics and post-selection algorithm. We discuss the potential of using this amplifier as a building block in extending the distance of quantum communication.