Researchers Demonstrate 3-Photon Split in the Microwave Domain

Researchers at the University of Waterloo have directly split one photon into three. To do so, they created a non-Gaussian state of light using spontaneous parametric down-conversion (SPDC).

Traditional SPDC, which splits a high-energy pump photon into two lower-energy photons, is a common way to produce entangled photon pairs. However, directly generating photon triplets through a single SPDC process has remained elusive.

The researchers used microwave photons to stretch the known limits of SPDC. Using a flux-pumped superconducting parametric cavity, they demonstrated direct three-photon SPDC, with photon triplets generated in a single cavity mode or split between multiple modes. The triplet source was bright, producing a propagating photon flux comparable to ordinary two-photon SPDC. The researchers observed strong three-photon correlations in the output photons. The symmetry properties of these correlations allowed them to “fingerprint” how the photons were created.

The observed states were strongly non-Gaussian, which, according to the researchers, has important implications for potential applications. “Non-Gaussian states and operations are a critical ingredient for obtaining the quantum advantage,” professor Chris Wilson said. “They are very difficult to simulate and model classically, which has resulted in a dearth of theoretical work for this application.”

The observed non-Gaussian, third-order correlations could represent an important step forward in quantum optics and could have a strong impact on quantum communication with microwave fields as well as continuous-variable quantum computation.

“The two-photon version has been a workhorse for quantum research for over 30 years,” Wilson said. “We think three photons will overcome the limits and will encourage further theoretical research and experimental applications and hopefully the development of optical quantum computing using superconducting units.” Through ongoing work, the researchers aim to show that the photons are entangled.

The research was published in Physical Review X (www.doi.org/10.1103/PhysRevX.10.011011).