Single site addressing in optical lattices
We spatially resolve and manipulate ultracold atoms in an optical lattice. Addressing of individual lattice sites is achieved through a high resolution optical imaging system, which allows for the detection and manipulation of cold atoms with sub-wavelength resolution.
Experimental setup
- Addressing single lattice sites
The central part of the experiment is an ultra-high resolution imaging system. It allows us to optically resolve atoms in neighboring sites of an optical lattice which are spaced by 532nm. The high resolution objective images the fluorescence light of the atoms located at the individual lattice sites onto a CCD camera with single photon detection capability. A specific advantage of this technique is that all lattice sites within the field of view are detected simultaneously. The objective is designed to operate at two wavelengths 420 nm and 780 nm, corresponding respectively to the 5S1/2 à 6P3/2 and the 5S1/2 à 5P3/2 transitions of 87Rb. The imaging system has a numerical aperture of NA = 0,70 (solid angle = 14%), yielding a diffraction limited resolution d = 1,22lambda/(2NA) of 370 nm for lambda = 420 nm and of 680 nm for lambda = 780 nm. The objective can also be used to focus an addressing laser onto single lattice sites.
High resolution images
- First high resolution images
We recently obtained the first high-resolution images (see Fig. 2). One can clearly distinguish individual atoms. The image has been obtained by first loading an ultracold gas close to the BEC transition into an optical lattice. Then the atoms were illuminated with a near-resonant 2D optical molasses at 780 nm. Since the depth of focus of the imaging system is only 2 μm, only atoms in the cental part of the cloud (diameter 30 μm) produce sharp images. The part out of focus produces a blurry background. In order to remove this background, we isolated only a few planes in the 3D lattice by an adiabatic microwave transfer in a magnetic field gradient. We obtain typically 30 photons per atom before it is lost from the trap. The observed spot size from single atom is about 700 nm and well matches the expected size of the point spread function.
Goals
In our setup, it will become possible not only to probe and to observe the system at the scale of a lattice site, but also to manipulate the particles on that fundamental microscopic length scale. Using the addressing technique described above, one could, e.g., flip the spin of a single atom at one lattice site and observe the ensuing dynamics of the many-body system. This would open the way to the study of non-equilibrium dynamics of a strongly correlated quantum system.
Ultracold atoms in optical lattices are also suitable for scalable quantum computing. In the Mott insulator regime, one can obtain exactly one atom per lattice site. This system represents a ”quantum register”, with 50-100 of qubits in one dimension or of several thousand atoms in two dimensions, in which the quantum state of each qubit could be manipulated and read out with high fidelity. Quantum gates and entanglement can be achieved either by collisions in a spin-dependent lattice or by Rydberg gates.
People
| Dr. Stefan Kuhr | Project leader |
| Dr. Jacob Sherson | Postdoc |
| Dr. Marc Chenau | Postdoc |
| Christof Weitenberg | PhD canditate |
| Manuel Endres | PhD canditate |
| Rosa Glöckner | Diploma student |
| Ralf Labouvie | Diploma student |