Researchers detect single photon with nanowire
Researchers from the FOM Foundation, Delft University of Technology and Eindhoven University of Technology are the first to have successfully detected single light particles (photons) using a semiconducting nanowire. They produced a nanodetector that converts the photons into electrons and that amplifies the electrical signal enough to be able to measure this. The researchers published the results of these electrical measurements on 20 May online in Nature Photonics. The measurement of single photons is vitally important for quantum communication.
Quantum computers will allow us to perform calculations much faster in the future. Different computers can only collaborate if they can exchange information over large distances. Scientists think that single photons would be suitable information carriers for this purpose. The computer would convert the photons into electrons and then process these further as an electric signal. However in order to make that signal usable it first of all needs to be considerably amplified. And that is what makes the design for a photon detector so complicated.
Avalanche of electrons
The new detector consists of a nanowire, which at one end absorbs photons and at the other emits an electrical current. The starting point is a quantum dot, a very small 'box' that absorbs a single photon with the correct colour and subsequently releases a single electron. This electron escapes from the box and ends up in the nanowire where resulting collisions with other electrons produces an avalanche of moving electrons. Eventually more than 10,000 electrons are set in motion by a single starting electron. By measuring this macroscopic current the researchers can distinguish between a single photon or no photon.
Detector design
The materials used to produce the nanowire are vital for the functioning of the detector. The researchers used a nanowire made from indium phosphide with a diameter of about 100 nm and a length of several micrometres. One end is covered with a layer of sulphur and the other with zinc in order to be able to produce a constant electric field. This field accelerates the electrons that move through the nanowire giving these enough energy to collide and produce more moving electrons. This results in an enormous avalanche of moving electrons that give rise to a current large enough to detect single photons.
Contact
Gabriele Bulgarini
Reference
G. Bulgarini, M.E. Reimer, M. Hocevar, E.P.A.M. Bakkers, L.P. Kouwenhoven and V. Zwiller. ' Avalanche amplification of a single exciton in a semiconductor nanowire'. Nature Photonics (2012), doi:10.1038/nphoton.2012.110.