The quantum dot device consists of a transistor made of different layers of gallium arsenide and aluminium gallium arsenide. One of the layers consists entirely of quantum dots just nanometers across. The quantum dots are extremely sensitive to photons. A photon hitting the detector liberates an electron trapped in the one of the dots. A nearby conducting channel, just a few nanometres above the quantum dot layer, picks up the electron - which causes a detectable change in the resistance of the channel. Currently the device only operates at 4 Kelvin but the team hopes to develop detectors that will work at 77 Kelvin and, eventually, at room temperature.