Physicist Eric Baalbergen of Leiden University (Netherlands) has defended a dissertation on detectors capable of distinguishing one, two and three photons - particles of light. The work, titled "Photon-number resolution using superconducting nanowires," was presented on November 3. Such detectors are an important building block for the optical quantum computer of the future.
Conventional light detectors can only record whether photons are present or not. For quantum computing this is not enough: the computer uses photons for calculations, and it is necessary to know precisely how many particles arrived at a given point simultaneously. "Our detector measures exactly how many light particles there were, and these measurements also provide information about how reliable the result is," Baalbergen explains. According to him, this is a small but fundamentally important step forward, although the detector still requires refinement.
The device is based on superconducting nanowires: extremely thin filaments of a material that loses electrical resistance at very low temperatures. When a photon hits such a wire, its electrical state changes and a measurable signal arises. One of the technical solutions is a clever connection of the detector to the electronics that read out the signal, which makes it possible to lose less of the electrical signal.
During the work, Baalbergen collaborated with theorist Ilse Kuijf, also a doctoral student at Leiden University. She studies how improved data analysis and new artificial intelligence methods help extract more information from experiments already conducted. Together with student Lars Selden teis, they proposed analyzing not only the amplitude of the electrical signal but also how it changes over time. This made it possible to determine the number of detected photons more accurately. The method places relatively low demands on the readout electronics, so it is fast and simple to apply. The results were published in the journal APS Open Science in July.
The detector is only one of the components of an optical quantum computer, but each of them is important for the development of the technology. Over time, quantum computers will be able to perform complex calculations that are extremely difficult for ordinary machines, for example helping to better understand chemical reactions and design new molecules and materials. The advantage of an optical quantum computer over a superconducting one is that almost all of its components operate at room temperature, without a bulky cooling system down to almost absolute zero, which saves money and time.
During the research, Baalbergen collaborated with the company QuiX Quantum. In the summer of 2026 it launched the first working prototype of an optical quantum computer. The scientist expects that his detector will be part of the next generation of this machine and will make it possible to carry out calculations with even greater precision.