Quantum storage of entangled telecom-wavelength photons in an erbium-doped optical fibre
Using atomic frequency comb protocol in a 20-meter erbium-doped fiber, this work demonstrates 1532 nm photon storage with high fidelity and preserved entanglement.
Key Findings
Methodology
This work employs spontaneous parametric down-conversion (SPDC) to generate time-bin entangled photon pairs at 795 nm and 1532 nm. The 1532 nm photon is filtered and stored in a 20-meter erbium-doped fiber using the atomic frequency comb (AFC) protocol. The AFC is created by spectral tailoring of inhomogeneously broadened Er3+ ions, forming a periodic absorption structure with 8 GHz bandwidth and 200 MHz peak spacing. The collective atomic excitation, described by a superposition of atomic states, re-emits the photon after 5 ns due to phase rephasing. The setup includes polarization analyzers, superconducting nanowire single-photon detectors (SNSPDs), and density matrix tomography to verify entanglement preservation. The process maintains a fidelity of 0.808±0.048 and entanglement of formation around 0.5 after storage.
Key Results
- The stored and retrieved 1532 nm photon maintains a fidelity of 0.808±0.048, with a storage efficiency of about 1%. The entanglement of formation remains high, decreasing from 0.531±0.011 to 0.499±0.105, indicating minimal degradation. Bell tests show S-values of 2.38±0.05 before and 2.33±0.22 after storage, both violating the classical limit of 2. The bandwidth of the AFC is 8 GHz, with a storage duration of 5 ns, demonstrating broadband, multi-mode capability. These results confirm that non-classical entangled states can be reversibly stored in fiber-based quantum memories, paving the way for practical quantum networks.
Significance
This work marks the first realization of telecom-wavelength non-classical photon storage in fiber, leveraging existing telecom infrastructure. It addresses a long-standing challenge in quantum communication—storing entangled photons at 1550 nm—by using erbium-doped fibers. The approach simplifies system architecture, enhances bandwidth, and enables integration into current fiber networks. The ability to preserve entanglement during storage is crucial for quantum repeaters and long-distance quantum communication. This breakthrough opens avenues for scalable quantum networks, quantum internet, and fundamental studies of light-matter interactions in fiber materials.
Technical Contribution
The study innovatively applies AFC protocol in erbium-doped fibers, utilizing spectral tailoring and magnetic field control to create broadband, multi-mode quantum memories. It combines commercial fiber technology with cryogenic cooling, enabling practical, scalable quantum storage. The integration of polarization analysis, density matrix tomography, and Bell tests demonstrates robust entanglement preservation. The work introduces a new platform for fiber-based quantum memories, bridging the gap between quantum optics and telecom infrastructure, with potential for high bandwidth and multi-mode operation.
Novelty
This is the first demonstration of broadband, multi-mode, non-classical photon storage directly in erbium-doped optical fiber at telecom wavelength. Unlike previous crystal-based approaches, this work uses commercially available fiber, greatly simplifying the setup and enhancing practicality. The application of AFC protocol in fiber, combined with magnetic field tuning, achieves high bandwidth (8 GHz) and preserves entanglement, representing a significant step forward in fiber quantum memories and scalable quantum networks.
Limitations
- The storage efficiency remains low (~1%), limiting practical deployment. The storage duration is only 5 ns, insufficient for long-distance quantum communication. System stability depends heavily on temperature and magnetic field control, complicating real-world implementation. Further improvements are needed to extend storage time and boost efficiency, which are critical for scalable quantum repeaters and networks.
Future Work
Future efforts will focus on increasing storage efficiency, extending storage times, and integrating the system into larger quantum networks. Exploring multi-mode and longer-duration storage, optimizing spectral tailoring, and improving system stability are key directions. Combining this approach with quantum repeater architectures could enable long-distance quantum communication. Additionally, integrating on-chip photonics and superconducting detectors may lead to scalable, compact quantum memory modules suitable for deployment in existing fiber infrastructure.
AI Executive Summary
This groundbreaking work demonstrates the reversible storage of entangled telecom-wavelength photons in a 20-meter erbium-doped fiber using the atomic frequency comb protocol. By generating time-bin entangled photon pairs at 795 nm and 1532 nm via SPDC, the researchers successfully stored the 1532 nm photon in fiber, maintaining high fidelity (0.808±0.048) and quantum entanglement after retrieval. The experimental setup involved spectral tailoring of erbium ions, magnetic field tuning, and advanced polarization and density matrix analysis. Bell inequality violations confirmed that entanglement persisted through the storage process, with S-values exceeding the classical limit both before and after storage. The AFC bandwidth of 8 GHz and a storage time of 5 ns demonstrated broadband, multi-mode capability, crucial for scalable quantum networks. This fiber-based quantum memory leverages existing telecom infrastructure, offering a practical pathway toward long-distance quantum communication. Although current efficiency is limited, the results establish a vital proof-of-concept, opening avenues for high-bandwidth, fiber-compatible quantum memories. Future work aims to enhance efficiency and storage duration, bringing quantum repeaters and quantum internet closer to reality. This achievement bridges the gap between quantum optics and fiber communication, marking a significant milestone in quantum information science.
Deep Dive
Abstract
The realization of a future quantum Internet requires processing and storing quantum information at local nodes, and interconnecting distant nodes using free-space and fibre-optic links. Quantum memories for light are key elements of such quantum networks. However, to date, neither an atomic quantum memory for non-classical states of light operating at a wavelength compatible with standard telecom fibre infrastructure, nor a fibre-based implementation of a quantum memory has been reported. Here we demonstrate the storage and faithful recall of the state of a 1532 nm wavelength photon, entangled with a 795 nm photon, in an ensemble of cryogenically cooled erbium ions doped into a 20 meter-long silicate fibre using a photon-echo quantum memory protocol. Despite its currently limited efficiency and storage time, our broadband light-matter interface brings fibre-based quantum networks one step closer to reality. Furthermore, it facilitates novel tests of light-matter interaction and collective atomic effects in unconventional materials.