Coincidence circuit
Walther Bothe's coincidence circuit was the first AND logic gate. It was developed to detect cosmic ray events, and other particles, in 1924. The techniques influenced several fields of technology, e.g. the design of RADAR circuits in the 1940s. The main idea of coincidence detection is that if a detector detects some particle ("clicks" in the jargon) this is quite likely (with a certain probability p) not a real event but (thermal or other) noise. But if two detectors click simultaneously, the probability that it is still a noise event (or a "dark count", as quantum optics people call it) is extremely reduced -- the probability is now p2. This technique hence greatly improves signal-to-noise ratio. However, for this to work, the coincidence circuit needs to have a suitable "coincidence window", i.e. must be able to differentiate between two signals which come at the same time from those which have too much (e.g. more than a few microseconds) temporal distance. Designing such electronics was a major achievement at Bothe's time and earned him (shared with Max Born) the 1954 Nobel Prize in physics.
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