Researchers have shown that when photons are created in pairs, they can emerge from different, rather than the same, locations. The discovery, which is in contrast to the general belief that photon pairs must originate from single points in space, could impact the study of quantum physics. “Until now, it has been assumed that such paired photons come from the same location,” said professor David Andrews of the University of East Anglia. “Now, the identification of a new delocalized mechanism shows that each photon pair can be emitted from spatially separated points, introducing a new positional uncertainty of a fundamental quantum origin.” Researchers were studying spontaneous parametric down-conversion (SPDC), a process in which photon beams are passed through a crystal to generate entangled pairs of photons, when they discovered a novel mechanism involved in the creation of paired light particles. The physical mechanism, which operated through virtual photon propagation, provided for photon pairs to be emitted from spatially separated sites of photon interaction. Occasionally, pairs were produced in which each photon emerged from a different point in space. The extent of nonlocalized generation was influenced by individual variations in both distance and phase correlation. Mathematical analysis of the global contributions from this mechanism provided researchers with a quantitative measure for a degree of positional uncertainty in the origin of down-converted emission. The entanglement of the quantum states in each pair has applications in quantum computing and other areas of quantum physics. The findings are also significant because they place limits on spatial resolution. “Everything has a certain quantum 'fuzziness' to it, and photons are not the hard little bullets of light that are popularly imagined,” Andrews said. Quantum entanglement is widely used in labs in numerous processes from quantum cryptography to quantum teleportation. For further information about the University of East Anglia, visit: http://uea.ac.uk/. The research was published in Physical Review Letters (doi.org/10.1103/PhysRevLett.118.133602).