We work at the boundary between Cold Atom and Condensed Matter physics.
2D Cold Atom Quantum Simulator
This project aims for the realization of Feynman's vision of simulation of a quantum system using a well controlled and model quantum system evolving according to a tailored Hamiltonian. Using cold atom systems in optical lattices, this stepwise approach is likely to quite naturally deliver one of the main currently foreseen applications of a quantum computer: a general quantum simulator.
The features of this ultracold Bose-Fermi mixture experiment are the high degree of control of the many-body system due to Feshbach resonances and the high optical resolution of the imaging and possible optical manipulation system by using two long range microscope objectives. The use of a 2D-3D-MOT combination which can be easily expanded to more species, as well as magnetic transport from the collection chambers to the science chamber, enables us to study problems governed by either Bose-Einstein or Fermi-Dirac statistics as well as mixtures of species.
Apart from looking into fundamental quantum physics problems this project also concentrates on developing and testing new technologies for ultracold atom experiments. Next to a miniaturised ultrastable laser system for cooling, trapping and detecting we also developed a compact coil design for magnetic transport and Feshbach resonances. Furthermore we looked into different vacuum sealing techniques for windows.
First atoms in an optical lattice
We have realised the first loading of an optical lattices produced by a spatial-light modulator. The atoms are held in the one beam optical dipole trap when the optical lattice is imposed. We have created one- and two-dimensional structures. This work will be continued towards atoms in multi-wells combined with higher optical resolution for imaging and manipulation.
By applying differently shaped imprint masks we managed the creation of long lived small density dips. They are accommodated with a phase step across them and move with in the potential. So far the longest observed features lived for more than 500 ms.
Dark 2D solitonic waves
We report to our knowledge on the observation of the first two-dimensional solitons in an ultra-cold atom experiment. The phase of the Bose-Einstein condensate is phase engineered with a spatial light modulator and let to evolve in the trapping potential. The pictures show the cloud after time-of-flight at different hold times (1 ms—5 ms). Top left shows the movement of the soliton with ca. 1.5 mm/s and bottom left depicts the premature decay of the soliton due to dissipation.
Bose-Einstein condensation of Rubidium
We have achieved the first Bose-Einstein condensate of Rubidium in our combined-species Rubidium-Potassium apparatus. The condensate was obtained after magnetically transporting a cloud of laser-cooled atoms in a science cell, and performing evaporative cooling first in the magnetic trap and then in a light dipole trap. The pictures below show the anisotropic expansion of the condensate at different time-of-flight times. The thermal cloud, seen as a halo, expands isotropically. The BEC has a temperature of approximately 100 nK.
Achievement of Bose-Fermi mixtures in a magneto-optical trap
The first mixed magneto-optical trap for bosonic rubidium (87Rb) and fermionic potassium (40K) in the Quantum Matter group has been realised. In the 2D Quantum Simulator project, the atoms are first trapped in a 2-dimensional magneto-optical trap to create a cold atom beam and then transferred by a pushing beam into another vacuum chamber where both species are retrapped by a six beam magneto-optical trap. The picture shows the fluorescence image of the magneto-optical trap for potassium in presence of the rubidium cloud (not visible). We trap 109 rubidium atoms with 106 potassium atoms.
- Figure: CAD design of the experimental setup. Left: 2D - 3D MOT setups for different species. Right: 2D quantum gas chamber with lattice beams and microscope objectives.
Disorder Physics with Cold Atoms
Establishing a test case for the quantum simulator setup, we intend to map out the phase diagrams of 2D systems in the vicinity of localization phenomena from Anderson localization to glass phases. We plan to characterize the interplay of interactions and disorder using Feshbach tuning as well as site-resolved potential definition. Complementary to studies on fixed disorder we plan to explore the phase diagram for mobile impurities in a quantum gas mixture of 40K and 87Rb, using the potassium atoms as "impurities". One focus of the investigations will lie on "polaron-like" self trapping phenomena.
Gallery (click for larger view)
- Top: 2 dimensional magneto-optical trap (2D MOT) for both Rb and K. Bottom: collection chamber, science chamber (glass cell on the left) and magnetic transport coils and rail.
- Miniature ultrastable laser system.
- Compact coil design for magnetic transport.
- Fluorescence image of a Potassium 40 magneto-optical trap.