Spontaneous Parametric Down-Conversion: Photon Pair Generation

For my PhD in Atomic & Laser Physics at the University of Oxford, I create pairs of photons to be used for quantum information experiments. A photon is a particle of light, and by creating a single pair, we can explore exotic and fascinating properties of quantum mechanics, like entanglement.

To create pairs of photons, a powerful laser (represented by the pianist's hands driving the music) is guided into a non-linear crystal (the laboratory). When the laser interacts with the crystal, pairs of photons (the dancers) are generated -- a process known as spontaneous parametric down-conversion. The generated photons have half the energy of a laser photon to satisfy energy conservation (hence the lower "red frequency" dress and tie).

Even when a photon pair leaves the crystal (the lab), they continue down the same path. It is only when they are separated by a polarizing beam-splitter that the two photons are forced in different directions, because of their different polarizations. These photons are generated spontaneously and would otherwise be impossible to measure without destroying them; therefore they are intentionally separated so that one can be detected to herald the existence of the other. We can use the remaining photon as a carrier of quantum information for our various applications.

Many thanks to Professor Ian Walmsley, all my fellow Ultrafast Quantum Optics colleagues, and to the UK Engineering and Physical Sciences Research Council (bloqs.org) for their generous support.

Dancers: Merritt Moore (PhD student), Nuno Fernandez
Choreographer: Michelle Kane
Videographer/Editor: Sandy Strallen
Music: “Libertango” by Piazolla
Performed by: Michel Camilo & Tomatito from “Spain Again” (Decca Records)
Use of track with kind permission of the artists