Scientists Achieve Telecom-Compatible Quantum Entanglement with Room-Temperature Memory

Insider Brief

• Researchers achieved entanglement between a telecom-wavelength photon and a room-temperature quantum memory, demonstrating a practical approach for large-scale quantum networks.
• The system operates without cryogenic cooling or complex frequency conversion, making it compatible with existing fiber-optic infrastructure while maintaining high entanglement fidelity.
• While atomic diffusion currently limits storage time, proposed improvements such as anti-relaxation-coated vapor cells could enhance long-distance entanglement distribution.

A team of Qunnect researchers has demonstrated entanglement between a telecom-wavelength photon and a room-temperature quantum memory, marking another step toward scalable quantum networks. The study, published on the pre-print serve arXiv, reports that the system successfully entangles telecom-wavelength photons with quantum memory at a reliability of up to 90.2%. The system can generate 1,200 entangled photon-memory pairs per second with 80% accuracy, meaning it creates a steady stream of reliable quantum links, a crucial step toward building practical quantum networks.

Entanglement distribution through existing fiber-optic infrastructure will be a prerequisite for large-scale quantum communication, but distance constraints and signal loss have long hindered progress. Quantum repeaters — devices that store and retransmit entangled photons — are considered essential for overcoming these barriers. The new study presents an approach based on room-temperature rubidium vapor, offering a simpler and more scalable alternative to conventional cryogenic or laser-cooled systems.

“The technical simplicity and robustness of our room-temperature systems paves the way towards deploying quantum networks at scale in realistic settings,” the researchers wrote in their paper.

By eliminating the need for quantum frequency conversion, the system maintains native compatibility between photon sources and quantum memories, reducing the complexity of quantum network architecture. The reported entanglement fidelity approaches levels seen in state-of-the-art cold atom systems while significantly reducing operational overhead. The extra time, energy, or resources needed to keep a system running efficiently is referred to as operational overhead, and in quantum networks, lower overhead means faster, more practical communication without costly delays or cooling requirements.

Methods and Experimental Setup

The study relied on rubidium-87 vapor for both photon generation and quantum memory, according to the paper. The researchers used a four-wave mixing process to produce entangled photon pairs, with one photon in the telecom band (1324 nm) and the other in the near-infrared band (795 nm). The telecom photon was sent through a fiber-optic channel while the near-infrared photon was stored in a rubidium-based quantum memory using electromagnetically induced transparency.

To benchmark performance, the researchers measured entanglement fidelity through quantum state tomography. The system achieved an entanglement fidelity of 86.5%, with a theoretical maximum of 90.2%. The photon-memory entanglement rate exceeded 1,200 pairs per second, a rate competitive with other leading quantum memory platforms.

“Our approach leverages identical atomic systems for both entangled photon pair generation and photon storage, directly establishing entanglement between a telecom photon (1324 nm) and a quantum memory without additional resources such as quantum frequency conversion (QFC),” the team writes.

Advantages and Challenges

Unlike other quantum memory platforms that require cryogenic cooling or complex laser cooling setups, the rubidium vapor-based system operates at room temperature. This advantage makes it more viable for real-world deployment, particularly in telecommunication networks where integration with existing infrastructure is a priority.

Another advantage is the high duty cycle of the quantum memory. “In our system, the overhead of preparing for memory operation — the downtime when the memory is unavailable for operation, is negligible: the only required step is the optical pumping that takes less than 1 microsecond. This feature makes our memory essentially ever-ready,” the researchers indicate.

In contrast, cold-atom-based memories require much longer cooling times, making them less practical for continuous operation in a networked environment.

However, the study also explains some of the limitations. The coherence time of the quantum memory, currently limited by atomic diffusion, constrains long-distance entanglement distribution. While the researchers achieved a utility time of up to 3 microseconds — sufficient for some applications — longer storage times will be necessary for large-scale quantum networks.

The team suggests that using anti-relaxation-coated vapor cells could significantly improve coherence time while maintaining high bandwidth.

Future Directions

The study lays the groundwork for practical quantum repeaters but acknowledges that further optimization is needed. Increasing laser power could improve memory bandwidth, while better filter designs could enhance signal-to-noise ratios.

“The current limitation stems solely from atomic diffusion, which can be addressed through anti-relaxation-coated vapor cells while maintaining high bandwidth performance,” the researchers state.

The researchers also point to the potential for deploying this technology in field trials, noting that their previous work has already demonstrated warm-vapor-based devices in metropolitan-scale networking testbeds. With continued development, these quantum repeaters could become integral to future quantum communication infrastructure, enabling secure global quantum networking.

For a more technical look at the researchers’ study, please review their paper on arXiv. Researchers often choose to publish in pre-print servers, such as arXiv, to receive faster feedback on their work, however, it is not officially peer-reviewed, a key step in the scientific method.

The Qunnect research team included Yang Wang, Alexander N. Craddock, Jaeda M. Mendoza, Rourke Sekelsky and Mael Flament