Step Toward Practical Quantum Networks
Quantum networks usually rely on entangled photons to carry information, but inevitable photon loss makes communication error prone. These errors can be reduced if receiving nodes send out a signal, called a herald, each time an entangled photon arrives. However, waiting for such heralds and repeating any failed transmissions greatly slow communication. Now Gianvito Chiarella and his colleagues at the Max Planck Institute of Quantum Optics in Germany have shown how to mitigate the problem by producing heralds at sending nodes instead of at receiving nodes [1].
In a typical quantum network, each node stores information in an atom, and the connection between nodes is established by entangling the atom with a photon that travels to the next node. The researchers realized that heralding such entanglement generation at sending nodes has three key advantages over heralding photon arrival at receiving nodes. First, the sending nodes can immediately react to unsuccessful entanglement attempts, eliminating long waits for network responses. Second, given that the heralds are produced locally, they are unaffected by the loss of photons en route to another node. And third, the heralds provide information about when entanglement was generated, enabling receiving nodes to better identify which photons are genuinely entangled.
In the team’s approach, each sending node contains an ultracold rubidium atom trapped at the center of two crossed optical-fiber cavities. After being excited by laser pulses, each atom decays and emits one photon into each of the two cavities. These cavities channel the photons in such a way that while one is entangled with the atom and travels to the receiving node, the other heralds the entanglement’s generation. The researchers highlight how their heralding technique could be used to extend the range or increase the reliability of long-distance quantum communication.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.
References
- G. Chiarella et al., “Source of heralded atom-photon entanglement for quantum networking,” Phys. Rev. Lett. 135, 240802 (2025).