Quantum engineering of ultracold atoms 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. Laser beams create periodic optical potentials forming an artificial “crystal of light”. In the Mott insulator regime, one can trap exactly one atom per lattice site, which constitutes an array of individual quantum bits.
To fully exploit the possibilities of such a system for quantum computing, we need to detect and to manipulate individual atoms on their lattice sites - a feature that was missing so far in this type of experiments. Our new experimental setup overcomes this limitation. Its central part is an ultra-high resolution imaging system that images the fluorescence light of the trapped atoms 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 imaging system has a numerical aperture of NA = 0.70 yielding a diffraction limited resolution of 400 nm for λ = 420 nm and of 700 nm for λ = 780 nm.
The objective will also be used to focus an off-resonant addressing laser onto individual atoms. The laser field changes their resonance frequency with respect to the other atoms in the lattice, such that with an external microwave field local spin flips can be produced.

The possibility to detect and to manipulate the atoms individually on their lattice sites allows the conception of an entirely new generation of experiments in the fields of quantum information and quantum simulation. It will be possible to observe and to manipulate density, spin structure, and correlations at the scale of a lattice site. By directly counting the number of atoms on the individual lattice sites, we can measure the statistics of site occupancy, both in the superfluid and in the Mott insulator phases, and detect imperfections such as doubly occupied sites or vacancies.

Using this new tool, we propose to investigate steady-state and dynamical properties of low-dimensional systems, which could not be detected by the conventional time-of-flight images. We plan to engineer fast, high-fidelity, quantum gates using Rydberg states or collisions in a spin-dependent lattice and to create massively entangled systems as a resource for quantum computation.