An international research team achieved a longstanding milestone in quantum optics research — the direct generation of photon triplets. This result has been sought for years but never achieved until now. An illustration of the triple photon experiment. (Image: Institute For Quantum Computing) The breakthrough was made by Thomas Jennewein, Hannes Hübel, Deny Hamel and Kevin Resch of the University of Waterloo, along with Alessandro Fedrizzi of the University of Queensland and Sven Ramelow of the Austrian Academy of Sciences. “This is going to open a new frontier of quantum optics and allow a new class of experiments in quantum computing using photons,” said lead investigator Jennewein. In the past, the generation of pairs of photons (particles of light) revolutionized quantum optics and made possible emerging technologies such as quantum cryptography and quantum computing with photons. Typically, these photon pairs were created from strong lasers sent through a crystal - a process known as “parametric down-conversion.” In the new approach, researchers created photon triplets by producing a first pair of photons using an optical crystal, then splitting one of the photon pairs further into two additional photons inside a second crystal. It’s a process that was first conceived 20 years ago, but had never before been experimentally observed. Because each triplet originates from a single pump photon, the quantum correlations will extend over all three photons in a manner not achievable when using independently created photon pairs. It is expected that this photon-triplet source will allow tests of novel quantum correlations and will greatly advance photonic quantum computing. Jennewein praised his collaborators and IQC’s research facilities for the fruitful results: “It shows the value of a very strong team and a great environment for allowing breakthroughs to happen.” In the research featured in the latest issue of the journal Nature, the researchers explain that these tripartite quantum correlations will significantly advance quantum information research. The project involved collaboration between IQC’s Quantum Photonics Laboratory and Quantum Optics and Quantum Information Group. The research was supported by the Canadian Institute for Advanced Research, the Ontario Centers of Excellence, the Ontario Ministry of Research and Innovation, the Natural Sciences and Engineering Council of Canada, and the Canadian Foundation for Innovation. For more information, visit: www.uwaterloo.ca