QR.N Paper reports experimental Advances toward reliable Quantum Networks –
In recent years, Quantum Networks have gained increasing attention in research. They have the potential not only to enhance the security of critical infrastructures but also to enable new applications, such as the secure interconnection of Quantum Computers. However, realizing such networks is technologically challenging. For instance, Quantum Communication suffers from unavoidable photon losses during transmission. These losses often prevent the successful creation of entangled Quantum States between distant nodes. A promising approach to address this problem is the use of “heralded” protocols: with suitable measurements at the sender or receiver node, it can be indicated whether the desired Quantum State was successfully generated. Failed transmissions can thus be reliably detected and discarded. Against this backdrop, a new paper involving the QR.N consortium was published in mid-December 2025.
The article presents an experiment demonstrating efficient, heralded generation of atom-photon entanglement. The aim is to reduce the error rate in Quantum Networks without unnecessarily lowering the effective communication rate. To achieve this, the researchers first generate the entanglement locally at the sending node. The core of the experiment involves a single atom that sequentially emits two photons via cascaded emission into two optical fiber resonators. The polarization of the first photon becomes entangled with the spin of the atom. Detection of the second photon reliably indicates that the desired atom-photon entanglement has been successfully created. By conditioning on successful events in this way, the efficiency of entanglement transmission through the fiber can be significantly increased.
In conventional heralded protocols, the heralding signal is typically generated at the receiving node. In contrast, the method described in the paper shifts this heralding to the sending node, offering several important advantages. First, the sender can immediately determine whether the atom-photon entanglement was successfully generated and, if necessary, start a new attempt right away. This avoids unnecessary waiting times and reduces communication overhead in the network. Second, the heralding signal does not need to travel over long distances and is therefore not subject to loss-induced attenuation, allowing detection with a high signal-to-noise ratio. Moreover, the heralding signal provides precise timing information about the moment of entanglement generation. When this information is communicated to the receiver, the expected arrival time of the entangled photon can be accurately predicted, enabling effective filtering of temporally uncorrelated events, particularly dark counts from the detectors.
Overall, this approach represents a major step forward for reliable, low-noise long-distance communication and could significantly extend the range of future Quantum Networks.
Source reference: https://journals.aps.org/prl/abstract/10.1103/5zk9-3rpv#physics_summar