Yes, photons can indeed be entangled, just like electrons and other quantum particles. Entanglement is a fundamental concept in quantum mechanics that describes a peculiar correlation between two or more particles, even when they are physically separated.
Entanglement occurs when the quantum state of a system cannot be described independently for each particle but instead must be described as a whole. When two particles become entangled, their quantum states become intertwined, and the state of one particle is instantly related to the state of the other, regardless of the distance between them.
Photons, as particles of light, can be entangled in various ways. One common method is through a process called spontaneous parametric down-conversion (SPDC). In SPDC, a high-energy photon is directed at a crystal, and it spontaneously splits into two lower-energy photons, known as entangled photon pairs. These entangled photons share a close relationship, with their properties, such as polarization, becoming correlated.
Entangled photons have been extensively studied in the field of quantum information and quantum communication. They have applications in areas like quantum cryptography, quantum teleportation, and quantum computing. The phenomenon of photon entanglement is a fascinating aspect of quantum mechanics and has been experimentally verified through numerous experiments.