Cross talk compensation in multimode continuous-variable entanglement distribution

TL;DR

This paper proposes a method to compensate for linear cross talk in multimode continuous-variable entanglement distribution, enhancing the robustness and efficiency of quantum networks.

Contribution

It introduces an optimization strategy involving initial squeezing and phase adjustments to fully counteract cross talk effects in multimode channels.

Findings

Optimizing initial squeezing reduces entanglement degradation.

Phase and coupling adjustments can fully compensate cross talk.

Method outperforms entanglement localization with measurement and feed-forward.

Abstract

Two-mode squeezed states are scalable and robust entanglement resources for continuous-variable and hybrid quantum information protocols at a distance. We consider the effect of a linear cross talk in the multimode distribution of two-mode squeezed states propagating through parallel similar channels. First, to reduce degradation of the distributed Gaussian entanglement, we show that the initial two-mode squeezing entering the channel should be optimized already in the presence of a small cross talk. Second, we suggest simultaneous optimization of relative phase between the modes and their linear coupling on a receiver side prior to the use of entanglement, which can fully compensate the cross talk once the channel transmittance is the same for all the modes. For the realistic channels with similar transmittance values for either of the modes, the cross talk can be still largely compensated. This method relying on the mode interference overcomes an alternative method of entanglement localization in one pair of modes using measurement on another pair and feed-forward control. Our theoretical results pave the way to more efficient use of multimode continuous-variable photonic entanglement in scalable quantum networks with cross talk.