How much quantum noise of amplifiers is detrimental to entanglement

TL;DR

This paper investigates how quantum noise from amplifiers affects entanglement in Gaussian states, revealing that symmetric amplification can destroy entanglement beyond a certain gain threshold, while asymmetric amplification is more resilient.

Contribution

It provides a quantitative analysis of entanglement degradation due to quantum noise in different amplification scenarios for Gaussian states.

Findings

Entanglement vanishes when phase insensitive amplification exceeds a specific gain threshold.

Asymmetric amplification preserves entanglement more effectively than symmetric amplification.

The threshold gain depends on the initial entanglement quantified by logarithmic negativity.

Abstract

We analyze the effect of the quantum noise of an amplifier on the entanglement properties of an input state. We consider both phase insensitive and phase sensitive amplification and specialize to Gaussian states for which entanglement measures are well developed. In the case of phase insensitive amplification in which both the modes are symmetrically amplified, we find that the entanglement in the output state vanishes if the intensity gain exceeds a limiting value $2/(1+\exp[-E_N])$ where $E_N$ is the logarithmic negativity of the input state which quantifies the initial entanglement between the two modes. The entanglement between the two modes at the output is found to be more robust if only one mode is amplified.