Entanglement Preservation and Clauser-Horne Nonlocality in Electromagnetically Induced Transparency Quantum Memories

TL;DR

This paper develops a theoretical model showing that electromagnetically induced transparency (EIT) quantum memories can preserve entanglement and nonlocality if the storage efficiency exceeds approximately 89.7%, addressing a key challenge in quantum information science.

Contribution

It provides the first systematic theoretical proof that EIT quantum memories can preserve entanglement and nonlocality under realistic conditions.

Findings

Decoherence transforms pure Bell states into mixed states.

A critical storage efficiency threshold of 89.7% is identified.

Above this threshold, nonlocality is preserved in the retrieved photons.

Abstract

Entanglement preservation in noisy quantum memories represents a long-standing conceptual challenge in quantum information science. While experiments have shown that electromagnetically induced transparency (EIT) memories can store entangled photons, a rigorous theoretical demonstration of whether such memories fundamentally preserve nonlocality has remained elusive. Here we develop a unified open-system model that combines the dark-state polariton formalism with reduced density operator theory to describe the retrieved photon state under realistic ground state decoherence. The analysis reveals that decoherence inevitably transforms an initially pure Bell state into a mixed state and predicts a critical storage efficiency threshold of 89.7%. Above this threshold, the retrieved photon violates the Clauser-Horne inequality, confirming the preservation of nonlocal quantum correlations, whereas below it, nonlocality is lost. This work provides the first systematic theoretical proof that EIT quantum memories can in principle preserve entanglement and nonlocality, thereby resolving a fundamental question in the physics of quantum information storage.