Quantum noise reduction in linear amplifiers

Horace P. Yuen

Compared with the use of phase-insensitive linear quantum amplifiers of the same gain G, the use of phase-sensitive linear amplifiers on phase coherent classical light sources in an amplifier-attenuator chain reduces the total quantum noise power by a factor of 4, the homodyne noise variance by 2, and the photon number variance by 2-8 and suppresses the Kerr effect linear phase fluctuation variance as well as the soliton timing-error variance by 2G(2).

M. W. P. Strandberg

Miguel Orszag

Jie Zhao, Josephine Dias, Jing Yan Haw +6 more

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.

Yin Qiang Li, Yijun Wang, Yun Jie Mao +3 more

An improved continuous variable quantum key distribution (CVQKD) approach based on a heralded hybrid linear amplifier (HLA) is proposed in this study, which includes an ideal deterministic linear amplifier and a probabilistic noiseless linear amplifier. The CVQKD, which is based on an amplifier, enhances the signal-to-noise ratio and provides for fine control between high gain and strong noise reduction. We focus on the impact of two types of optical amplifiers on system performance: phase sensitive amplifiers (PSA) and phase insensitive amplifiers (PIA). The results indicate that employing amplifiers, local local oscillation-based CVQKD systems can enhance key rates and communication distances. In addition, the PIA-based CVQKD system has a broader application than the PSA-based system.

Miguel Orszag