Photonic spatial Bell-state analysis for robust quantum secure direct communication using quantum dot-cavity systems

TL;DR

This paper proposes a robust, deterministic method for analyzing spatial Bell states of photons using quantum dot-cavity systems, enabling secure quantum communication resilient to environmental disturbances.

Contribution

It introduces a complete spatial Bell-state analyzer based on quantum dot-cavity interactions and a secure communication protocol leveraging this analysis.

Findings

The proposed BSA works in both strong and weak coupling regimes.

The protocol enhances robustness of quantum communication against decoherence.

The method utilizes quantum nondemolition detection via Faraday rotation.

Abstract

Recently, experiments showed that the spatial-mode states of entangled photons are more robust than their polarization-mode states in quantum communications. Here we construct a complete and deterministic protocol for analyzing the spatial Bell states using the interaction between a photon and an electron spin in a charged quantum dot inside a one-side micropillar microcavity. A quantum nondemolition detector (QND) for checking the parity of a two-photon system can be constructed with the giant optical Faraday rotation in this solid state system. With this parity-check QND, we present a complete and deterministic proposal for the analysis of the four spatial-mode Bell states. Moreover, we present a robust two-step quantum secure direct communication protocol based on the spatial-mode Bell states and the photonic spatial Bell-state analysis. Our analysis shows that our BSA proposal works in both the strong and the weak coupling regimes if the side leakage and cavity loss rate is small.