Coinidence counting
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In quantum physics, coincidence counting is used in experiments testing particle non-locality and quantum entanglement. In these experiments two particles are created from the same initial energy, inexorably linking/entangling their physical properties. Separate particle detectors measure the quantum states of each particle and send the resulting signal to a coincidence counter. There are many non-entangled particles which can strike either detector and add noise to the signal, so the coincidence counter only records the data if the signals arrived at the same time. This ensures that the data comes from an entangled source and can be used to calculate a Bell inequality or to perform a quantum eraser.
