RESEARCH: Novel work on repulsive interaction of photons

At the beginning of June, a paper titled ’ Repulsive photons in a quantum nonlinear medium’ was published in the renowned journal Nature Physics, with one of the authors being Dr Branislav Jelenković, a researcher of the Institute of Physics, Belgrade. Apart from Dr Jelenković, the authors of the paper are researchers of the Massachusetts Institute of Technology and Harvard University.

This work demonstrated control of strongly interactive photons, both repulsive and attractive, which can have a tremendous significance for quantum physics. Since photons pass each other without any interaction whatsoever, physicists require techniques to intensify these minuscule and imperceptible repulsive and attractive interactions.

Based on the paper of Martin Weitz’s group published in 2010, so far it has been known that it is possible to engineer attractive interactions between photons. However, repulsive interaction remained a challenge. In the new paper, the team from MIT and Harvard, which also includes our researcher Dr Jelenković, showed that it is possible to achieve both types of photon interactions through precise control of the interaction of photons and Rydberg atoms.
According to Dr Branislav Jelenković, such interactions among individual photons are demonstrated by two- and three-photon correlation functions. ’For these interactions, the non-linear environment is necessary whose role was taken on by a dense gas of cold Rb atoms’, says Dr Jelenković explaining that the success of the experiment was facilitated by an atomic schematic of two coupled EIT resonances, which he has studied with his colleagues from the Photonics Centre.

The experiment was carried out at the laboratory of Dr Vladan Vuletić, MIT professor, and the first listed author of the paper is his doctorate candidate Sergio Cantu, whose PhD thesis is based on the recently published paper. Professor Vuletić and Professor Mikhail Lukin of Harvard University have long collaborated in the field of quantum optics of ultra-cold atoms and they are members of the faculty of the Centre for Ultracold Atoms which was founded by professors of their scientific affiliations. The team of Dr Vuletić has for years cooperated with the Institute of Physics, Belgrade, predominantly Dr Jelenković who has been the most frequent guest of the MIT Laboratory and who, in 2017, participated in the setting up the aforementioned experiment and testing of its parts, as well as in the measurements in the following year.

The new experiment has succeeded in gaining a one-dimensional sequence of interacting atoms, but the success provides an opportunity to realize multi-dimensional photon crystals. For this to be possible, numerous challenges have to be overcome, one of which is more extensive interaction control. However, the newest success makes the whole idea on photon crystals more comprehensible, as Dr Jelenković states, and if it gets to be realized it will enable significant applications in quantum informatics and quantum metrology.

Original paper in the journal Nature Physics: Repulsive photons in a quantum nonlinear medium