Hong-Ou-Mandel effect

The Hong-Ou-Mandel effect is a quantum phenomenon where two identical photons, arriving simultaneously at a beamsplitter, always exit together through the same output port rather than separately. When quantum interference occurs, this behavior causes a noticeable reduction in coincident detections of the photons at different outputs, creating a "dip" in the measurement signal. This effect demonstrates the wave-like nature of photons and their quantum entanglement, playing a key role in quantum information and communication technologies. Essentially, it reveals how indistinguishable particles can exhibit collective behaviors that defy classical expectations.