Jonas Hammer, Markus Lippl, in collaboration with the group of Maria Chekhova at MPL
This activity is a collaboration with the group of Maria Chekhova and it started almost 10 years ago. It aims at studying the generation of correlated sidebands of pairs of photons (low-gain) and twin-beams (high-gain) in hollow-core photonic crystal fibres filled with noble gases. The use of noble gasses prevents Raman scattering, which is usually detrimental for the coherence of quantum states generated in fibres. Adjusting the gas pressure in the fibre allows to finely tune the phase-matching condition of the nonlinear process.
Another promising application of engineered optical fibres is the direct generation of photon triplets. This process, which can be viewed as the quantum conjugate of third-harmonic generation has not yet been reported in the optical frequency domain. Sub-micron tapered fibres embedded in a gas-cell, which allow fine tuning of the dispersion, seems to be the most promising approach.
 M. Finger et al., PRL 115, 143602 (2015)
 A. Cavanna et al., Phys. Rev. A 101, 033840 (2020)
 J. Hammer et al., Opt. Lett. 43, 2320 (2018)
 J. Hammer et al., Phys. Rev. Res. 2, 012079(R) (2020)
Florian Schorn, Yu Zhong
This collaboration with the department of chemical and biological engineering has been started lately. By utilizing a hollow-core fibre as reactor, the light can be used for efficiently probing the various compounds of the chemical reaction. The combination of tight confinement and long interaction length allows single-pass spectroscopic measurements using less than µl volume of chemicals with good accuracy. In this way the limitations of both, the chromatographic and the in-situ spectroscopic approach for a classical reaction screening can be circumvented.
As a proof of principle, we used nonlinear Raman spectroscopy for a reaction screening of the acidic catalysed esterification of methanol and acetic acid.
Dual beam trapping is widely used because it can guide particles into a hollow-core photonic fibre (HC-PCF) and the trapping in it is very stable. The protected environment provided by the HC-PCF is an ideal system to study the Optomechanics. Lately we started experiments with magnetic particles made of Yttrium Iron Garnet (YIG). The aim is to study the magneto-optical coupling. We recently trapped YIG particles in front of HC-PCF via the dual-beam trapping. By improving the trapping and studying the properties, the applications on the photon-magnon coupling will be further extended.
Daniel Häupl, in collaboration with the group of Robert Löw at the 5. Institute of physics in Stuttgart
This project aims to combine atomic physics with fibre optics. By trapping light inside hollow-core photonic crystal fibres we aim to enhance the interaction between atoms and light. One application is to generate THz radiation, where the increased interaction length will result in higher emission rates compared to free space.
Another aim is to make the setup even more integrated, to allow for a much more versatile and easier-to-use tool.
 G. Epple, et al., Nat. Comm., 5:4132, 2014.
 G. Epple, et al., Opt. Lett., 42 (17):3271–3274, 2017