QUROPE Quantum Information Processing and Communication in Europe

Atom chips are a promising candidate for a scalable architecture for quantum information processing provided a universal set of gates can be implemented with high fidelity. The difficult part in achieving universality is the entangling two-qubit gate. We consider a Rydberg phase gate for two atoms trapped on a chip and employ optimal control theory to find the shortest gate that still yields a reasonable gate error. Our parameters correspond to a situation where the Rydberg blockade regime is not yet reached.

We investigate the use of a Bose-Einstein condensate trapped on an atom chip for making interferometric measurements of small forces. A fundamental limit on sensitivity is imposed by the noise in the energy difference of the split condensates, which we measure and explain. We also consider systematic errors. A leading effect is the variation of rf magnetic field in the trap with distance from the wires on the chip surface. This can produce energy differences that are comparable with those due to gravity.

We present a versatile and compact electron beam driven source for alkali metal atoms which can operate even with a heat dissipation of less than 1mW, and can therefore be implemented inside a closed cycle cryostat. Atoms are loaded into a Magneto-Optical Trap (MOT) and at a given thermal input power, loading rates three orders of magnitude higher than in a typical MOT loaded by an alkali metal dispenser are achieved.

Atom chips provide a versatile `quantum laboratory on a microchip' for experiments with ultracold atomic gases. They have been used in experiments on diverse topics such as low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. A severe limitation of atom chips, however, is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far.