A team of researchers has confirmed that even when one photon is split into two, the total angular momentum remains exactly the same. The study, published in Physical Review Letters, used a setup sensitive enough to catch only a few successful events out of billions.
In light, there are two forms of angular momentum: orbital angular momentum (OAM) and rotation. OAM describes a structured wavefront and comes in whole-number steps. The team tested the conservation of OAM at the smallest possible scale, using spontaneous parametric down conversion (SPDC).
The researchers sent single photons into a second crystal to see whether each quantum of OAM is conserved. They built two down conversion stages in sequence, a design called Cascaded SPDC. This approach allowed them to move from averages to one photon at a time.
To verify the rule for inputs of zero, minus one, and plus two, the team shaped and analyzed spatial modes with programmable optics and single mode fibers. They also built correlation matrices that show which input and output OAM values appear together.
The results confirmed that OAM is conserved even when driven by a single photon. The study paves the way for more ambitious tests of quantum foundations and capable quantum networks.
Source: https://www.earth.com/news/scientists-split-a-single-photon-and-observed-an-important-law-of-physics-in-action