Conference key agreement in a quantum network

TL;DR

This paper demonstrates that using GHZ states in a quantum network significantly improves conference key rates over traditional pair-wise methods, with experimental validation on a six-user photonic network.

Contribution

It introduces a protocol leveraging GHZ states for efficient multi-user quantum conference key agreement and experimentally verifies its advantage over pair-wise protocols.

Findings

Over two-fold increase in key rate with GHZ states

Experimental validation on a six-user quantum network

Resource advantage persists with finite-key effects

Abstract

Quantum conference key agreement (QCKA) allows multiple users to establish a secure key from a shared multi-partite entangled state. In a quantum network, this protocol can be efficiently implemented using a single copy of a N-qubit Greenberger-Horne-Zeilinger (GHZ) state to distil a secure N-user conference key bit, whereas up to N-1 entanglement pairs are consumed in the traditional pair-wise protocol. We demonstrate the advantage provided by GHZ states in a testbed consisting of a photonic six-user quantum network, where four users can distil either a GHZ state or the required number of Bell pairs for QCKA using network routing techniques. In the asymptotic limit, we report a more than two-fold enhancement of the conference key rate when comparing the two protocols. We extrapolate our data set to show that the resource advantage for the GHZ protocol persists when taking into account finite-key effects.