Researchers at Tampere University, working with colleagues in Germany and India, have demonstrated for the first time that angular momentum remains conserved when a single photon splits into two. This result confirms a core principle of physics at the quantum scale and marks a milestone that could help in creating advanced quantum states for use in computing, communication, and sensing technologies.
Conservation laws are central to science because they determine which processes are possible and which are not. A familiar example is seen in billiards, where the momentum of one ball transfers to another during a collision. A similar principle applies to objects that spin, which carry angular momentum. Light, too, can possess angular momentum, specifically orbital angular momentum (OAM), which relates to the spatial shape of a light beam.
At the quantum level, this means that individual photons carry specific amounts of OAM that must be preserved when they interact with matter. In a study recently published in Physical Review Letters, the Tampere-led team investigated whether this conservation rule still applies when a lone photon is divided into a pair. Their work pushed the limits of conservation testing to the smallest possible scale.
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