Robust entanglement distribution via telecom fibre assisted by an asynchronous counter-propagating laser light

TL;DR

This paper demonstrates a robust method for distributing entangled photon pairs over 1 km of optical fibre using a decoherence-free subspace formed by independent light sources, enabling high-visibility interference without active synchronization.

Contribution

It introduces a novel approach utilizing fully independent light sources and asynchronous photons for entanglement distribution over telecom fibre, enhancing robustness against noise.

Findings

Successful distribution of entangled photons over 1 km fibre

High-visibility interference achieved without active synchronization

Use of independent sources in a decoherence-free subspace

Abstract

Distributing entangled photon pairs over noisy channels is an important task for various quantum information protocols. Encoding an entangled state in a decoherence-free subspace (DFS) formed by multiple photons is a promising way to circumvent the phase fluctuations and polarization rotations in optical fibres. Recently, it has been shown that the use of a counter-propagating coherent light as an ancillary photon enables us to faithfully distribute entangled photon with success probability proportional to the transmittance of the optical fibres. Several proof-of-principle experiments have been demonstrated, in which entangled photon pairs from a sender side and the ancillary photon from a receiver side originate from the same laser source. In addition, bulk optics have been used to mimic the noises in optical fibres. Here, we demonstrate a DFS-based entanglement distribution over 1km-optical fibre using DFS formed by using fully independent light sources at the telecom band. In the experiment, we utilize an interference between asynchronous photons from cw-pumped spontaneous parametric down conversion (SPDC) and mode-locked coherent light pulse. After performing spectral and temporal filtering, the SPDC photons and light pulse are spectrally indistinguishable. This property allows us to observe high-visibility interference without performing active synchronization between fully independent sources.