Highly-Efficient Quantum Memory for Polarization Qubits in a Spatially-Multiplexed Cold Atomic Ensemble

TL;DR

This paper demonstrates a highly efficient quantum memory for polarization qubits using a spatially-multiplexed cold atomic ensemble, achieving over 68% efficiency and 99% fidelity, enabling reversible qubit mapping for quantum networks.

Contribution

It introduces a spatially-multiplexed cold atomic ensemble quantum memory with high efficiency and fidelity, surpassing previous limitations in qubit storage performance.

Findings

Achieved 68% storage-and-retrieval efficiency.

Maintained over 99% fidelity in qubit storage.

Demonstrated reversible mapping with more information retrieved than lost.

Abstract

Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information science and technology. A critical figure of merit is the overall storage-and-retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. Here we report on a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and an efficiency equal to (68$\pm$ 2)%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. Our work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.