QUROPE Quantum Information Processing and Communication in Europe

We introduce a new approach to assess the error of control problems we aim to optimize. The method offers a strategy to define new control pulses that are not necessarily optimal but still able to yield an error not larger than some fixed a priori threshold, and therefore provide control pulses that might be more amenable for an experimental implementation. The formalism is applied to an exactly solvable model and to the Landau–Zener model, whose optimal control problem is solvable only numerically.

Quantum communication is built on a set of disruptive concepts and technologies. It is driven by fascinating physics and by promising applications. It requires a new mix of competencies, from telecom engineering to theoretical physics, from theoretical computer science to mechanical and electronic engineering. First applications have already found their way into niche markets, and university labs are working on futuristic quantum networks, but most of the surprises are still ahead of us.

• Quantum Optics and Quantum Information
• Novel Laser Phenomena And Non Linear Atom And Photon Optics
• Cold Matter Non-Linear Optics In A Coherently Prepared Molecular Medium
• Ion Traps and Laser Cooling
• Confined Atoms And Atoms In External Fields
• Strong Field Theory
• Laser Development And Modelling
• Shaping Of High Intensity Laser Pulses
• Molecules In Strong Fields
• High Intensity Laser Interactions With Nanoparticles

Physicists at MPQ control the optical properties of a single atom!

Due to the continued miniaturization of computer chip components, we are about to cross a fundamental boundary where technology can no longer rely on the laws of the macroscopic world. With this in mind, scientists all over the world are researching technologies based on quantum effects that can be used to communicate and process information. One of the most promising developments in this direction are quantum networks in which single photons communicate the information between different nodes, e.g. single atoms. There the information can be stored and processed. A key element in these systems is Electromagnetically Induced Transparency (EIT), an effect that allows to radically change the optical properties of an atomic medium by means of light. Previously, scientists have studied this effect and its amazing properties, using atomic ensembles with hundreds of thousands of atoms. Now, scientists in the group of Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics (MPQ) in Garching and Head of the Quantum Dynamics Division, have managed to control the optical response of a single atom using laser light (Nature, Advanced Online Publication, DOI: 10.1038 /nature09093). While representing a corner stone in the development of new quantum based technologies, these results are also fundamental for the understanding of how the quantum behaviour of single atoms can be controlled with light.

Researchers in Cambridge in the UK have succeeded in generating entangled photons using electricity alone, with a new device called an "entangled light-emitted diode" (ELED). The device converts electrical current directly into entangled light rather than relying on laser power as in previous technology. The technique could be a practical way to integrate many entangled light sources together on a single chip – something that will be crucial for making a real-world optical quantum computer.

We have fabricated and tested an atom chip that operates as a matter wave interferometer. In this communication we describe the fabrication of the chip by ion-beam milling of gold evaporated onto a silicon substrate. We present data on the quality of the wires, on the current density that can be reached in the wires and on the smoothness of the magnetic traps that are formed. We demonstrate the operation of the interferometer, showing that we can coherently split and recombine a Bose–Einstein condensate with good phase stability.

We investigate a setup where a cloud of atoms is trapped in an optical lattice potential of a standing-wave laser field which is created by retroreflection on a micromembrane. The membrane vibrations itself realize a quantum mechanical degree of freedom. We show that the center-of-mass mode of atoms can be coupled to the vibrational mode of the membrane in free space. Via laser cooling of atoms a significant sympathetic cooling effect on the membrane vibrations can be achieved. Switching off laser cooling brings the system close to a regime of strong coherent coupling.

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.