Controllably releasing long-lived quantum memory for photonic polarization qubit into multiple separate photonic channels

TL;DR

This paper demonstrates a method to controllably release long-lived quantum memories for photonic polarization qubits into multiple channels with high fidelity, advancing quantum information storage and retrieval capabilities.

Contribution

It introduces a technique to release stored photonic polarization qubits into multiple channels with high fidelity using cold atoms and electromagnetic-induced transparency.

Findings

Achieved controllable release into 7 channels.

Maximum quantum-process fidelity of 94.2% at 0.85 ms.

Fidelity remains above 78% at 6 ms, surpassing Bell inequality violation threshold.

Abstract

We report an experiment in which long-lived quantum memories for photonic polarization qubits (PPQs) are controllably released into any one of multiple separate channels. The PPQs are implemented with an arbitrarily-polarized coherent signal light pulses at the single-photon level and are stored in cold atoms by means of electromagnetic-induced-transparency scheme. Reading laser pulses propagating along the direction at a small angle relative to quantum axis are applied to release the stored PPQs into an output channel. By changing the propagating directions of the read laser beam, we controllably release the retrieved PPQs into 7 different photonic output channels, respectively. At one of the output channels, the measured maximum quantum-process fidelity for the PPQs is 94.2% at storage time of t= 0.85ms. At storage time of 6 ms, the quantum-process fidelity is still beyond 78%, the threshold for the violation of the Bell inequality. The demonstrated controllable release of the stored PPQs may extend the capabilities of the quantum information storage technique.