Christian Kurtsiefer

We present the strategic framework and technical foundations behind the development of the National Quantum-Safe Network (NQSN) in Singapore—a resilient, fully interoperable quantum-safe network. The testbed features a star-topology architecture built on production-grade fiber infrastructure, supporting multi-protocol quantum key distribution (QKD) and diverse applications from multiple vendors. A centralised key and network management system underpins its interoperability, enabling seamless integration across technologies. We further explore a range of quantum-secured use cases, including data center connectivity, edge computing, hybrid QKD–post-quantum cryptography (PQC) encryption, and multi-layer integration within the OSI stack. These technical insights demonstrate the feasibility and flexibility of deploying quantum-safe capabilities in a multi-input, multi-output network environment.

The National Quantum-Safe Network (NQSN) in Singapore is a nationwide collaborative platform and a field-deployed test-bed aimed at demonstrating quantum-safe cryptography solutions. NQSN links up academic, public and private members, targets trials for quantum key distribution (QKD) network with different QKD protocols, post-quantum cryptography (PQC) and classical symmetric key technologies.

Clock synchronization is necessary for communication and distributed computing tasks. In quantum communication systems, photo-detection events need to be discriminated with sub-nanosecond accuracy in order to distill information from correlations at a sufficiently high rate. This typically entails significant resource overheads, such as the use of ultra-stable frequency references, that will also scale with the number of communicating endpoints.

Violation of a Bell inequality can be used to generate certified random numbers. Given the high rate at which pairs of entangled photons can be produced, they constitute promising candidates for high rate randomness generation. However, this requires closing the detection loophole. Here we present our progresses toward an experimental demonstration of randomness generation with photons, certified by the violation of a Bell inequality with a closed detection loophole.