QUROPE Quantum Information Processing and Communication in Europe

Considerable efforts are currently devoted to the preparation of ultracold neutral atoms in the emblematic strongly correlated quantum Hall regime. The routes followed so far essentially rely on thermodynamics, i.e. imposing the proper Hamiltonian and cooling the system towards its ground state. In rapidly rotating 2D harmonic traps the role of the transverse magnetic field is played by the angular velocity.

 We propose a scheme involving cold atoms trapped in optical lattices to observe different phenomena traditionally linked to quantum–optical systems. The basic idea consists of connecting the trapped atomic state to a non-trapped state through a Raman scheme. The coupling between these two types of atoms (trapped and free) turns out to be similar to that describing light–matter interaction within the rotating–wave approximation, the role of matter and photons being played by the trapped and free atoms, respectively.

 We study the ground state phases of the S = 1=2 Heisenberg quantum antiferromagnet on the spatially anisotropic triangular lattice and on the square lattice with up to next-next-nearest neighbor coupling (the J1J2J3 model), making use of Takahashi’s modified spin-wave (MSW) theory supplemented by ordering vector optimization. We compare the MSW results with exact diagonalization and projected-entangled-pair-states calculations, demonstrating their qualitative and quantitative reliability.

We provide a general quantum theory to describe the coupling of light with the motion of a dielectric object inside a high finesse optical cavity. In particular, we derive the total Hamiltonian of the system as well as a master equation describing the state of the center of mass mode of the dielectric and the cavity field mode. In addition, a quantum theory of elasticity is used in order to study the coupling of the center of mass motion with internal vibrational excitations of the dielectric.

We explore the behavior of the phonon number distribution in an heterogeneous linear ion crystal. The presence of ion species with different masses changes dramatically the transverse energy spectrum, in such a way that two eigenfrequencies become non-analytic functions of the mass ratio in the form of a sharp cusp. This non-analyticity induces a quantum phase transition between condensed and conducting phase of the transverse local phonons.

We report transport operations with linear crystals of 40Ca+ ions performed by applying complex electric time-dependent potentials. For their control we use the information obtained from the ions’ fluorescence. We demonstrate that by means of this feedback technique, we can transport a predefined number of ions and also split and unify ion crystals.

Mit einzelnen Photonen lässt sich die Bahn eines Atoms beobachten und mittels der Lichtkraft eines Laserstrahls für einige Millisecunden speichern.

We describe a versatile planar Penning trap structure, which allows to dynamically modify the trapping configuration almost arbitrarily. The trap consists of 37 hexagonal electrodes, each of 300 mikron diameter, fabricated in a gold-on-sapphire lithographic technique. Every hexagon can be addressed individually, thus shaping the electric potential. The fabrication of such a device with clean room methods is demonstrated.

Atom optics employs the modern techniques of quantum optics and laser cooling to enable applications which often outperform current standard technologies. Atomic matter wave interferometers allow for ultra-precise sensors; metrology and clocks are pushed to an extraordinary accuracy of 17 digits using single atoms. Miniaturization and integration are driven forward for both atomic clocks and atom optical circuits.