Breakthrough in superconducting light detectors


(By: LION news)
A team of Dutch and Swiss researchers has managed to successfully scan the surface of a superconducting light detector in very high detail. Amongst them is Jelmer Renema, researcher at the Leiden Institute of Physics (LION). The new technique they used could dramatically change the design of light detectors. These devices have many applications, amongst others in quantum information technology.

Superconducting light detectors are well equipped to measure individual photons. For this reason, these devices have become very popular in science and technical applications – for example communication with space probes and monitoring cancer therapies.

‘The problem with superconducting light detectors is, however, that they cannot observe every single entering photon,’ says Renema. ‘Up until now the reason behind that was unclear. We have established the cause of this limitation; certain parts of the detector are less sensitive to light than others. When a photon hits one of these areas, chances are that it remains undetected.’

Within the light detector is a flat nano wire - about 5 nanometer thick and 100 nanometer wide - which is folded very precisely, such that it forms a tightly packed, winding pattern. When a photon hits the wire, the detector immediately notices a small voltage peak. The researchers discovered that the middle of the wire has more trouble detecting light than the edges. For successful detection, a small whirlpool of electric current needs to form at the edge of the wire. When the photon directly hits this area, the process is more efficient.

The research team reached this conclusion by scanning the detector’s surface with a specially designed exposure technique. They targeted the detector with light of two different polarisations. Afterwards, they subtracted one measurement from the other. In this way, they created a higher contrast image than usual, which enabled the researchers to observe details that were previously invisible. The research was conducted by scientists from FOM, Leiden University (LION), TU Eindhoven and Zurich University, as part of the FOM programme ‘Nanoscale Quantum Optics’.

Superconducting light detectors play an important role in quantum communication - an encrypted communication technique that involves photons in a secret quantum state. This communication is more efficient with superconducting light detectors. Bank transactions and other discrete messages are fundamentally safe with quantum communication. Also quantum computers could use this type of communication. These computers work in a principally different way than regular computers and are much faster, creating a whole range of revolutionary applications.