Direct measurement of decoherence for entanglement between a photon and stored atomic excitation

Abstract

Violations of a Bell inequality are reported for an experiment where one of two entangled qubits is stored in a collective atomic memory for a user-defined time delay. The atomic qubit is found to preserve the violation of a Bell inequality for storage times up to 21 microseconds, 700 times longer than the duration of the excitation pulse that creates the entanglement. To address the question of the security of entanglement-based cryptography implemented with this system, an investigation of the Bell violation as a function of the cross-correlation between the generated nonclassical fields is reported, with saturation of the violation close to the maximum value allowed by quantum mechanics.

4 pages, 3 figures. Minor changes. Published version

References in corpus (2)

• Deterministic single photons via conditional quantum evolution
• Efficient retrieval of a single excitation stored in an atomic ensemble

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