The VQCC attended the Theory of Quantum Computation, Communication, and
Cryptography (TQC) conference held at the University of Aveiro, Portugal.


Three researchers from the VQCC attended the Theory of Quantum Computation, Communication, and Cryptography (TQC) conference held at the University of Aveiro in Portugal in July 2023. TQC is a leading annual international conference for students and researchers working on the theoretical aspects of quantum information science. Its main aim is to gather the community and discuss the latest advancements in the field. The event’s agenda covered a wide array of subjects, including quantum computing, quantum information, quantum sensing, and quantum hardware. It featured keynote speeches, contributed talks, various poster sessions, and an industry session.

During the conference, Xoel Sixto presented his recent work on decoy-state quantum key distribution (QKD) with non-uniform phase randomization. Decoy-state QKD requires the phase of each signal to be uniformly random, which can be hard to guarantee in practice due to device imperfections or the use of an external phase modulator for phase randomization purposes, which limits the possible phase values to a finite set. Xoel’s work introduced the first security proof for imperfect active phase randomization, bridging the gap between QKD theory and practical use.

Dr. Álvaro Navarrete, on the other hand, discussed his research on Trojan Horse attacks. Most security proofs for QKD overlook leaks from users’ devices, leaving them susceptible to Trojan-horse attacks (THAs). THAs involve injecting light into QKD systems to uncover internal settings. While few recent studies address this, they suggest that the effectiveness of QKD suffers without strong device isolation. Álvaro’s work establishes security boundaries for decoy-state QKD against THAs, outperforming past analyses and narrowing the gap between QKD theory and implementation.

Lastly, Dr. Víctor Zapatero shared his latest research on a fully passive approach to quantum key distribution. This promising technique removes optical modulators and random number generators from QKD hardware. This shift might simplify QKD systems, make them immune to modulator side channels, and possibly increase repetition rates. Notably, Víctor also played a key role in analysing the security of a passive decoy-state BB84 protocol demonstrated by researchers from the University of Science and Technology of China. This demonstration occurred recently and highlights the potential of passive approaches.