Feasibility of 300 km Quantum Key Distribution with Entangled States

TL;DR

This paper demonstrates the feasibility of 300 km quantum key distribution using entangled photon states over a free-space link, showing it surpasses the distance limits of weak coherent pulse systems.

Contribution

The study experimentally verifies that entanglement-based QKD can operate over 300 km with high channel loss, especially when the entangled photon source is centrally located.

Findings

Entanglement-based QKD exceeds 300 km range with high channel loss.

Placement of the entangled photon source in the middle enhances feasibility.

Experimental results confirm theoretical predictions about loss tolerance.

Abstract

A significant limitation of practical quantum key distribution (QKD) setups is currently their limited operational range. It has recently been emphasized (X. Ma, C.-H. F. Fung, and H.-K. Lo., Phys. Rev. A, 76:012307, 2007) that entanglement-based QKD systems can tolerate higher channel losses than systems based on weak coherent laser pulses (WCP), in particular when the source is located symmetrically between the two communicating parties, Alice and Bob. In the work presented here, we experimentally study this important advantage by implementing different entanglement-based QKD setups on a 144~km free-space link between the two Canary Islands of La Palma and Tenerife. We established three different configurations where the entangled photon source was placed at Alice's location, asymmetrically between Alice and Bob and symmetrically in the middle between Alice and Bob, respectively. The resulting quantum channel attenuations of 35~dB, 58~dB and 71~dB, respectively, significantly exceed the limit for WCP systems. This confirms that QKD over distances of 300~km and even more is feasible with entangled state sources placed in the middle between Alice and Bob.