Professor Greentree's work has led to two entirely new fields in physics: the Jaynes-Cummings-Hubbard Model, or Solid Light; and Spatial Adiabatic Passage.
The Jaynes-Cummings-Hubbard model provides a way to generate new phases of light by generating effective photon-photon interactions. This opens up effects from Condensed Matter Physics to Quantum Optics, such as insulator to superfluid phase transitions. Since his initial publication in 2006, there have been hundreds of follow up articles from groups world-wide. This includes theoretical and experimental studies as well as popular summaries in press releases, Wikipedia, and New Scientist. The first experimental demonstration appeared in 2019 [Ma et al. Nature 566, 51 (2019)].
He proposed spatial adiabatic passage as a robust way to transport electrons around a quantum dot array or phosphorus in silicon quantum computer. This idea led to a patented quantum computer architecture. Additionally Longhi, an Italian physicist, translated his approach into waveguide optics and now spatial adiabatic passage is being used to construct new photonic devices. Groups developing this approach include Jena, Milano, and ANU.
Prof Greentree, with Prof Brant Gibson, initiated a collaboration with Prof Tanya Monro (then at the University of Adelaide) to explore how to integrate nanodiamonds in optical fibres for single photon development. This collaboration has blossomed into the development of many hybrid diamond glass structures, including most recently a collaboration with DST Group on the development of robust diamond-glass magnetometers.
In addition to diamond-glass structures, he has explored the possibilities of using diamond hybrid materials for biological and surgical applications with my colleague Dr Kate Fox (RMIT). We have created diamond-polycaprolactone composites for tissue scaffold applications, as well as shown improvements in titanium by the addition of diamond nanoparticles.
Most recently, he developed a novel approach to diamond magnetometry termed Laser Threshold Magnetometry. Thi led to three patent applications, a new collaboration with Dr Jan Jeske, who is pursuing aspects of this work at the Fraunhofer Institute, Freiburg Germany, and an emerging collaboration with Drs Morgan Schmidt and Luke Bissel of the Air Force Research Laboratories (USA).
His research has also recently branched into understanding the psychophysics and numerical competency of bees. He collaboratea with the group of A/Prof Adrian Dyer (RMIT) and Dr Aurore Avarguès-Weber (Toulouse). Together, they have shown that bees (Apis Mellifera) can be trained to understand the concept of zero [Howard et al., Science 360, 1124 (2018)], and even to perform elementary tasks related to addition and subtraction [Howard et al., Science Advances 5, eaav0961 (2019)]. These two papers had considerable media impact, with Altmetrics scores of 1495 and 1838 respectively, as of 14/12/2020.