Photon Efficiency of High-Dimensional Quantum Key Distribution

TL;DR

This paper analyzes the efficiency of high-dimensional entanglement-based quantum key distribution in satellite communications, demonstrating that multiqubit encoding significantly improves secret key rates under realistic conditions.

Contribution

It introduces an optimized approach for encoding multiple qubits per photon pair to maximize QKD efficiency in satellite scenarios.

Findings

Optimal efficiency occurs at a finite photon pair production probability.

Multiqubit encoding can increase secret key rates by up to ten times.

Efficiency is maximized by balancing source intensity and encoding complexity.

Abstract

We investigate entanglement-based quantum key distribution protocols, with particular emphasis on their efficiency under realistic conditions of satellite quantum communications, where performance is limited by the low power of a received signal and background radiation. We focus on scenarios where each photon pair is used to encode multiple qubits in order to optimally utilize the weak signal. By optimizing over the source intensity and the number of encoded qubits we study the theoretical information limit for the QKD efficiency. We show that the optimal efficiency is attained for finite entangled photons pair production probability which is in contrast to conventional communication efficiency maximized in the limit of vanishing signal strength. The multiqubit encoding can enhance the secret key rate by up to an order of magnitude compared to single-qubit schemes.