Independent Photons Coalesce

Quantum mechanics predicts that when two photons emitted simultaneously by parametric down-conversion and sharing identical mode properties meet at opposite sides of a beamsplitter, they will coalesce and depart the beamsplitter in the same direction. Researchers at Stanford University in California and NTT Basic Research Laboratories in Kanagawa, Japan, have demonstrated that the effect applies to consecutively (or independently) emitted photons.

Their source was a semiconductor quantum dot sandwiched between two mirrors to form a microcavity. As they scanned the delay time between consecutive photons to zero, the scientists observed that the photons began to depart through the same output, indicating that they were coalescing.

The results of the experiment, in the Oct. 10 issue of Nature, may advance scientists' ability to create logic gates for photon-based quantum computing.