Quantum Optics Group (LMU) - Quantum Many Body Systems Division (MPQ)

Single-site Detection and Manipulation in Optical Lattices

Ultracold quantum gases in optical lattices have evolved in the last years into an interdisciplinary tool for many-body solid state and quantum physics. In our experiment we developed techniques to detect and manipulate single Rubidium atoms in a two-dimensional optical lattice. This allows for the study of the system response to local pertubations and give us access to novel observables such as multi-site correlations in the many-body system.

Measured atom distribution of an ultracold quantum gas held in a two-dimensional optical lattice. For the BEC (left), a random atom distribution in the lattice is observed, whereas for strong repulsive interactions between the atoms, an ordered Mott insulating state (middle & right) is formed.

Experimental setup

Addressing single lattice sites

Detection of individual lattice sites is achieved through a high resolution optical microscope that images the fluorescence light of the trapped atoms onto a CCD camera. A specific advantage of this technique is that all lattice sites within the field of view are detected simultaneously. The imaging system has a numerical aperture of NA = 0.68 yielding a diffraction limited resolution of 700 nm for λ = 780 nm.

We use the same microscope objective for the optical addressing of individual lattice sites. Arbitrary intensity distributions can be projected onto the atoms, which are generated with the help of a digital mirror device. Combining this technique with microwave radiation we can control the atomic hyperfine state locally.

Quantum Magnetism In Optical Lattices

Observation of free and bound Magnons in the dynamics after a local excitation.

Using two internal atomic hyperfine states we realized the 1D ferromagnetic Heisenberg model in our optical lattice. This quantum spin model describes the motion of spins on 1D chains as well as their next-neighboor interactions. We were able to study the motion of individual Magnons, the elementary excitations of the Ferromagnet. Furthermore, we observed bound Magnon states direcly by their characteristic spin correlations.

Long Range Interactions Via Rydberg States

Schematic illustration of the long range interactions between Rydberg atoms extending over several lattice sites.

Interactions in cold atom systems usually have a very short range. These contact interactions lead to the onsite energy shift for multiply occupied sites in an optical lattice and drive the superfluid to Mott-Insulator transition. For spin systems they lead to effective next neighbor interactions, however, at the cost of a drastically decreased magnitude. Rydberg atoms offer the possibility to realize very strong, effectively long range, interactions. We study the resulting long range interacting quantum spin models experimentally using our microscope. One unique feature of our approach is the direct imaging of the Rydberg excitations in the interacting many-body system. Using this technique we were able to study spontaneously ordered quantum states of Rydberg excitations.


Picture of the Laser setup providing the light to manipulate the atoms [Picture (c) Axel Griesch].
Dr. Christian GroßProject leader
Dr. Jun Rui
Dr. Johannes ZeiherPostdoc
Antonio Rubio AbadalPhD student
Simon HollerithPhD student
David WeiMaster student

Former members:

Prof. Dr. Stefan KuhrProject leader
Frauke SeeßelbergMaster student
Ahmed OmranMaster student
David BellemDiploma student
Dr. Sebastian HildPhD student
Dr. Peter SchaußPhD student
Dr. Manuel EndresPhD student
Dr. Christof WeitenbergPhD student
Dr. Jae-yoon ChoiPostdoc
Dr. Takeshi FukuharaPostdoc
Dr. Marc CheneauPostdoc
Dr. Jacob ShersonPostdoc
Ralf LabouvieDiploma student
Rosa GlöcknerDiploma student