Context

Direct generation of photon triplets via spontaneous third-order parametric down-conversion (TOPDC), which can be seen as the quantum reversal of the third-harmonic generation, has been a long-standing goal in the quantum optics and nonlinear-optics communities. Although the demonstration of TOPDC has recently been realized in the microwave range, it remains a challenging task in the optical range. A large number of theory papers, starting from the 1980s, discussed TOPDC as a source of the famous Greenberger-Horne-Zeilinger states and because it is the lowest-order nonlinear process leading to the generation of a non-Gaussian Wigner function, which is strongly desired in quantum information protocols. TOPDC is based on third-order nonlinearity, therefore optical fibers made from glasses are an ideal platform for its realization. This is in contrast to the common technique of photon pair generation (second-order parametric down-conversion), which is based on second-order nonlinearity and therefore has to be performed in nonlinear crystals.

Project

In this race towards the first demonstration of triplets, we have already studied several systems, including gas-filled hollow-core photonic crystal fibres, hybrid microstructured fibre and sub-micron tapered fibres. Due to chromatic dispersion, inter-modal phase-matching is required. Not only this strongly reduces the spatial pump-triplet overlap and hampers even more the efficiency of the process, but it also means that a high-order spatial mode is required as the pump. The current project is a continuation of our previous studies and will initially focus on the use of sub-micron tapered optical fibres, which seems to be the most promising candidate for the generation of triplets. In a first stage of the thesis, we plan to seed the process at one of the triplet frequencies. The presence of this seeding photon will trigger the generation of the complementary two photons. For each frequency ω1 of the seed, the two-photon source can be characterized. Next, we will explore the case of unseeded (spontaneous) TOPDC.

The project is a collaboration with the group of Quantum Radiation of Maria Chekhova at the Max-Planck Institute for the Science of Light in Erlangen. The project therefore combines nonlinear optics, photonics and quantum optics. The candidate should have a solid background in photonics. They will integrate the Joly’s group at the Friedrich-Alexander Universität and the Max-Planck Institute for the Science of Light in Erlangen.

Comments

Applications including cover letter, curriculum vitae, list of publications, and statement of research interests should be submitted via e-mail as a single PDF file. Please also arrange for at least two reference letters which should be sent directly to Prof. Joly. Application documents as well as any inquiries about the positions should be sent to Prof. Nicolas Joly (nicolas.joly@fau.de). Applications will be accepted until the positions are filled.