Entanglement sensitivity to signal attenuation and amplification

TL;DR

This paper investigates how continuous-variable entanglement behaves under signal attenuation and amplification, revealing fundamental noise limits and demonstrating the robustness of non-gaussian states in noisy quantum channels.

Contribution

It provides a comprehensive analysis of entanglement dynamics during attenuation and amplification, highlighting the resilience of non-gaussian states beyond quantum-limited noise levels.

Findings

Quantum-limited amplification destroys entanglement of Gaussian states with gain ≥ 2.

Non-Gaussian states with few photons can preserve entanglement beyond quantum noise limits.

High-energy Gaussian states are robust to asymmetric attenuation, while non-Gaussian states excel in symmetric conditions.

Abstract

We analyze general laws of continuous-variable entanglement dynamics during the deterministic attenuation and amplification of the physical signal carrying the entanglement. These processes are inevitably accompanied by noises, so we find fundamental limitations on noise intensities that destroy entanglement of gaussian and non-gaussian input states. The phase-insensitive amplification $\Phi_1 \otimes \Phi_2 \otimes \ldots \Phi_N$ with the power gain $\kappa_i \ge 2$ ($\approx 3$ dB, $i=1,\ldots,N$) is shown to destroy entanglement of any $N$-mode gaussian state even in the case of quantum limited performance. In contrast, we demonstrate non-gaussian states with the energy of a few photons such that their entanglement survives within a wide range of noises beyond quantum limited performance for any degree of attenuation or gain. We detect entanglement preservation properties of the channel $\Phi_1 \otimes \Phi_2$, where each mode is deterministically attenuated or amplified. Gaussian states of high energy are shown to be robust to very asymmetric attenuations, whereas non-gaussian states are at an advantage in the case of symmetric attenuation and general amplification. If $\Phi_1 = \Phi_2$, the total noise should not exceed $\frac{1}{2} \sqrt{\kappa^2+1}$ to guarantee entanglement preservation.