Singapore’s First Secure Quantum Network


A multinational team of researchers from the National University of Singapore (NUS) and LMU Munich has successfully shown a unique type of quantum key distribution (QKD) that is secure even if the consumers are unaware of the underlying quantum hardware (LMU). The study paves the path for a more open and secure quantum internet.

The device-independent QKD or DIQKD is the apex of secure key exchange and has the potential to transform how we handle risks and have faith in communication networks. According to Asst Prof Charles Lim, who proposed the project and started the collaboration with the LMU team, “important problems in cybersecurity, like supply chain attacks and side-channels, could be mitigated because this method enables users to validate their quantum hardware without trusting the manufacturers.”


The exchange of secret keys across a public channel is an essential requirement for secure communication. Modern methods for exchanging secret keys are based on the assumption that some mathematical problems are hard to answer using state-of-the-art computation. But considering the quick advancement of next-generation computing technologies like quantum computing, this approach might not be the best choice for applications that prioritize long-term security.


The key exchange issue has a long-term, reliable solution provided by QKD. By measuring and exchanging single photons, users can share a pair of identical, secret random keys. The main benefit of QKD is that it is the best option for long-term sensitive data protection because its channel security is mathematically impossible to breach. However, the execution of QKD, from the creation of quantum devices through side-channel attacks, must be faultless in order to realize this security promise, which is a big barrier in actuality.


The new investigation is based on DIQKD. It’s significant to note that the security of DIQKD is independent of the protocol’s use of quantum device specifications. However, there are two significant obstacles to putting DIQKD into practice. The system must be exceedingly effective at producing high-quality entanglement between the two users and have very little underlying quantum noise. Achieving these two conditions simultaneously over large distances has long been a challenge.


In order to solve the first problem, the researchers used a novel DIQKD technique. In contrast to other protocols, the protocol adds a second set of key-generating measurements for users. Due to the protocol’s increased resistance to noise and loss, information theft by eavesdroppers is made more challenging. This protocol was created by Asst Prof. Lim and associates at NUS.


The second challenge required the researchers to build a high-quality entanglement 400 meters apart between two quantum devices. Quantum switching is used in this case to achieve entanglement, and individual photons from locally generated photon-atom entangled pairs are sent via a 700-meter optical fiber and mixed in a joint measurement system.


On the other hand, while doing security analysis to determine whether the setup was capable of producing DIQKD secret keys, the researchers encountered a considerable experimental challenge in balancing entanglement quality, generation rate, and system noise. The researchers claim to be developing techniques to entangle distant quantum memories, which is a crucial step toward massive quantum networks. As the basis for long-distance quantum network links, the experiment revealed an entanglement distribution between distant quantum memories.


The Electrical and Computer Engineering Department and the NUS Centre for Quantum Technologies conducted this investigation at the NUS College of Design and Engineering. Through the NRF Fellowship program, the National Research Foundation (NRF) provided funding for it.