Photonic crystal fibres (PCF) consist of a microstructured cladding of periodically arranged air-channels surrounding the core region. They are an ideal platform for all sort of nonlinear optics experiments ought to the possibility to adjust nonlinearity and dispersion. These parameters are easily adjustable at the fabrication stage. Alternatively, pressurizing the fibre is a good way to modify online the dispersion landscape so as to ensure the phase-matching conditions required for a particular effect. We will present in this talk several experiments using pressure-assisted nonlinear optics for the generation of quantum optics sources. First, we will show broadly tunable photon-pair generation in a suspended core fibre that we filled with argon gas [Phys. Rev. Res., 2, 012079 (2020)]. When the hollow-core fibre is filled with noble gas i.e., monatomic, the fluid serves as the gain medium. Not only we can then adjust the dispersion landscape of the fibre but we can even prevent the Raman scattering originating from random molecular vibrations, that yields unwanted noise and degrades the quality of the fibre-based sources. Such a versatile system is becoming a promising platform in quantum optics as it allows the generation of frequency tunable pairs of photons through four-wave mixing or modulational instability [PRA 95, 053814 (2017)]. We will show in this presentation the creation of correlated photon pairs with frequency separation up to over an octave [Opt. Lett. 46, 4033 (2021)]. By contrast, we will see that if a coherent pattern of molecular vibrations is first prepared, stimulated Raman scattering can be utilized within its lifetime for thresholdless conversion of single photons, provided certain phase-matching conditions are fulfilled. We recently demonstrated frequency up-conversion of single photon by 125 THz, while preserving the correlation of the original entangled pair [Science, 376, 621 (2022)]. Finally, we will discuss the latest advances on the generation of triplet states, which can be regarded as the reverse process of the generation of third harmonic.

Nicolas Joly is an associate professor at the University of Nüremberg-Erlangen, where he works on photonic crystal fibers. He is also the head of the "microstructured optical fibres" research group at the Max-Planck Institute for the Science of light in Erlangen. His domain of research includes nonlinear optics as well as quantum-optics in PCF. In particular he is very interested in the nonlinear generation of new frequencies like supercontinuum generation or the generation of non-classical states of light using PCF.