Research activities
The research in Klaus Sengstock's group at the Institut für Laserphysik mainly concentrates on two major topics. Experiments dedicated to the field of ultracold quantum gases including bosonic, fermionic and mixed systems in trapping potentials of different geometry including e.g. optical lattices and hollow core photonic crystal fibres are complemented by research activities in the field of fibre laser development and state-of-the-art ultra-sensitive spectroscopy.
In the following you will find brief descriptions of the individual research projects, whilst the corresponding links provide more detail.
Spinor BEC
The goal of this project is a deep understanding of the physics of multi-component quantum gas systems. Loading a spinor BEC into a three-dimensional optical lattice provides an almost perfect experimental realization of solid state magnetism models and moreover constitutes a very promising candidate for quantum computation. A non-cubic optical lattice as implemented in our experiment will hopefully enable us to study additional effects such as spin frustration.
Bose-Fermi mixtures
In this project we investigate the properties of Bose-Fermi mixtures with emphasis on optical lattices. Bosonic Rubidium and fermionic Potassium as used in our experiment are idealy suited since moreover their interaction can readily be controlled via Feshbach resonances, which allows for the investigation of different regimes from nearly interaction-free to interaction dominated systems. Exploring new correlated quantum phases and the identification of composite particles lie consequaently at the heart of our research interests.
Ytterbium BEC
The major goal of this project is to combine the benefits of optical lattice clocks and ultracold degenerate quantum gases. For this purpose we currently set up a machine capable of the production of an ultracold Ytterbium-Rubidium mixture inside an optical lattice. The specific properties of Ytterbium, namely a very favorably distribution of natural abundances of various isotopes as well as a very narrow so called optical clock transition shall allow for measurements of interaction induced energy shifts with thus far unprecedented accuracy.
Guest and Bachelor Lab
This experiment is currently under construction. We are building a Rubidium-Potassium quantum gas mixture setup adapted to the special needs for education of Bachelor students. In addition, the experiment will play a central role in the guest programme of the ZOQ, as it is intended to serve as a user facility on which researchers from other institutes around the world can perform forefront research together with the local students in Hamburg.
Atom Guiding
Ultracold quantum gases in one-dimensional geometries are an intriguing field of research as they allow for strong nonlinear atom-light interaction and efficient matter wave guiding. In this experiment, we realize such a configuration by coupling laser light into a hollow core photonic bandgap fiber where the resulting dipole trap efficiently confines previously cooled 85Rb atoms to a transverse dimension of 12µm and guides them along the fiber.
BEC in Space
In earthbound experiments, studying the free evolution of a BEC is limited to less than 100 ms as the atoms fall out of the interrogation volume once released from their trap. This project overcomes this limitation by dropping a complete quantum gas setup down the 110 m high free fall tower at ZARM in Bremen allowing for a free expansion of 1 s. The system facilitates the investigation of the condensate's coherence in new regimes, the operation of highly sensitive atom interferometers and is an important stepping stone for future experiments on ballistic rockets or satellites.
Non-standard Hubbard models
This project theoretically explores the physics beyond standard Hubbard models. It focuses on orbital models and non-cubic lattices topologies. The interactions promote particles to higher bands of the lattice which has a strong impact on the tunneling and on-site interactions giving rise to new quantum phases. Lattice geometries such as the hexagonal graphene-like band structure offer novel possibilities for exploring interaction effects in complex systems. In particular, bosonic (spinor) systems and Bose-Fermi mixtures are investigated.
Atom trap trace analysis
In this project we want to refine a new method based on laser cooling and trapping to determine ratios of different isotopes of Kr with unprecedented sensitivity. Being a characteristic fission product in Plutonium breeding 85Kr is a sensitive tracer to detect non-compliance with the Non-Proliferation Treaty (NPT). We put special emphasis on an highly efficient all optical production of the rare-gas metastable states in Kr which are required for laser cooling in order to increase the overall efficiency. A strobed double-MOT set up with single-atom detection capability is at the heart of our experimental. This project is carried out in the Zentrum für Naturwissenschaft und Friedensforschung.
Intracavity absoprtion spectroscopy
Objective of this project is to develop Intracavity Absorption Spectroscopy (ICAS) technique suitable for ultrasensitive spectroscopic measurements of molecular and atomic absorption in various spectral regions. A high sensitivity of ICAS is achieved by placing the sample in the open part of the cavity of a multimode laser. The laser light passes through the absorber many times, and the intracavity absorption signal is accumulated in its spectrum, like in a multipass cell. The effective absorption path length extends here up to several thousands kilometres. The enhancement of the sensitivity and of the spectral range of ICAS is very important for various applications such as monitoring atmospheric pollutions, medical diagnostics by monitoring human exhalation, combustion diagnostics, etc.
Multicolor fiber lasers
Many applications, such as color displays, confocal microscopy, optical data storage, photo finishing, and therapeutic biomedical instruments require compact coherent light sources at different wavelengths in the visible range. Such sources can be realized with a single Pr/Yb-doped ZBLAN fiber, that is excited by a diode laser in the spectral range from 780 to 880 nm. The broad fluorescence spectrum of this fiber also includes especially important RGB (red, green, blue) colors. Selective dielectric mirrors placed to both ends of the fiber ensure the excitation of laser oscillations at the required wavelength. Laser emission at 492, 520, 535, 605, 612, 635 and 717 nm has been already demonstrated. Piezoelectrically controlled spectral reflection of the laser mirrors enables us to vary the spectral composition of the total laser emission.
Dynamics of multimode lasers
This project aims at a new and detailed understanding of the dynamics of multimode lasers. This knowledge is important for a variety of laser applications such as laser spectroscopy, intracavity frequency doubling, optical feedback and laser power stabilization.
