SEQOND (Single-photon Enhanced Quantum Optical Network Detector)

A quantum receiver that can catch and relay single particles of light without scrambling their fragile quantum information is being built and tested on a real quantum network. Today’s quantum networks—used for secure communications and future quantum computers—lose signal strength and fidelity over distance. Existing receivers are either too expensive, too bulky, or too error-prone to scale up. SEQOND tackles this by using a technique called upconversion, which shifts the wavelength of incoming single photons to a range where detectors work more efficiently, while keeping the quantum state intact. This allows the receiver to be both high-performance and low-cost, and it opens a route to link with quantum memories that store photons for later use. If the approach works, it could become a standard building block for entanglement distribution—the process that underpins quantum key distribution (unhackable encryption), distributed quantum computing, and the future quantum internet. The project is applied rather than curiosity-driven: it aims to deliver a working module that can be plugged into existing fibre networks. Success would quietly strengthen the infrastructure that will one day protect financial transactions, medical records, and government communications from quantum-enabled cyberattacks.