Experimental realization of large-alphabet quantum key distribution protocol using orbital angular momentum entanglement

TL;DR

This paper reports an experimental demonstration of a large-alphabet quantum key distribution protocol using entangled photons in orbital angular momentum states, achieving secure key sharing without the need for information reconciliation.

Contribution

It introduces a novel QKD protocol utilizing OAM entanglement with multiple phase holograms, enabling direct key retrieval without additional reconciliation steps.

Findings

Coincidence rates are distinct for different key elements.

Alice can fully recover Bob's keys without reconciliation.

The protocol shows potential for secure high-dimensional quantum communication.

Abstract

We experimentally demonstrate a quantum key distribution (QKD) protocol using photon pairs entangled in orbit angular momentum (OAM). In our protocol, Alice and Bob modulate their OAM states on each entangled pair with spatial light modulators (SLMs), respectively. Alice uses a fixed phase hologram in her SLM, while Bob designs $N$ different suitable phase holograms and uses them to represent his $N$-based information in his SLM. With coincidences, Alice can fully retrieve the key stream sent by Bob without information reconciliation or privacy amplification. We report the experiment results with N=3 and the sector states with OAM eigenmodes l=1 and l=-1. Our experiment shows that the coincidence rates are in relatively distinct value regions for the three different key elements. Alice could recover fully Bob's keys by the protocol. Finally, we discuss the security of the protocol both form the light way and against the general attacks.