Photons have been entangled through most of their obvious physical properties, such as polarization, position and momentum, and even angular momentum. Now, Lixiang Chen, at Xiamen University, China, and colleagues demonstrate entanglement via two new properties of photons with a specific cross-sectional structure. The researchers produced pairs of entangled photons with well-defined “radial position” and “radial momentum,” meaning each photon’s wave function is localized at a certain radius and moves radially inwards or outwards with a certain momentum. Measurements made at a pair of detectors showed that the positions and momenta of the photons were correlated. The observations indicate that a photon’s radial components may be useful for various applications, such as quantum cryptography and optical micromanipulation.

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