QUROPE Quantum Information Processing and Communication in Europe

In transport experiments the quantum nature of matter becomes directly evident when changes in conductance occur only in discrete steps, with a size determined solely by Planck's constant h. The observations of quantized steps in the electric conductance have provided important insights into the physics of mesoscopic systems and allowed for the development of quantum electronic devices. Even though quantized conductance should not rely on the presence of electric charges, it has never been observed for neutral, massive particles.

We demonstrate cooling of the motion of a single neutral atom confined by a dipole trap inside a high-finesse
optical resonator. Cooling of the vibrational motion results from electromagnetically induced transparency
(EIT)-like interference in an atomic \Lambda-type configuration, where one transition is strongly coupled to the cavity
mode and the other is driven by an external control laser. Good qualitative agreement with the theoretical
predictions is found for the explored parameter ranges. Further, we demonstrate EIT cooling of atoms in the

Quantum envoy is any activity connecting interested third-party audiences with the quantum information research community. Typical examples of quantum envoy are public lectures and exhibitions presenting general aspects of QIPC research and goals.

We study one-dimensional quantum walks in a homogenous electric field. The field is given by a phase which depends linearly on position and is applied after each step. The long time propagation properties of this system, such as revivals, ballistic expansion, and Anderson localization, depend very sensitively on the value of the electric field, Φ, e.g., on whether Φ/(2π) is rational or irrational. We relate these properties to the continued fraction expansion of the field.

We report on the experimental realization of electric quantum walks, which mimic the effect of an electric field on a charged particle in a lattice. Starting from a textbook implementation of discrete-time quantum walks, we introduce an extra operation in each step to implement the effect of the field. The recorded dynamics of such a quantum particle exhibits features closely related to Bloch oscillations and interband tunneling.

While the slogan “no measurement without disturbance” has established itself under the name of the Heisenberg effect in the consciousness of the scientifically interested public, a precise statement of this fundamental feature of the quantum world has remained elusive, and serious attempts at rigorous formulations of it as a consequence of quantum theory have led to seemingly conflict