QUROPE Quantum Information Processing and Communication in Europe

Cavity quantum electrodynamics (QED) provides a powerful tool to realize quantum nondemolition measurements of either part of the system, emitter or photon, by observing the effect of the interaction on the other part. Such ideal projective measurements allow to detect, to prepare and to manipulate quantum states in a controlled and coherent manner. They are used with atomic or solid-state emitters in the optical or microwave domain. So far, Rydberg atoms in cavity QED systems have mainly been used to measure or create quantum states of light.

Using modern micro and nano-fabrication techniques combined with super-conducting materials we realize quantum electronic circuits in which we create, store, and manipulate individual microwave photons. Making use of the strong interaction engineered between photons and quantum two-level systems we probe fundamental quantum effects of microwave radiation and develop components for applications in quantum technology.

Experimental methods to prepare cold samples of the few-electron molecules H2+, H2, He2+ and He2 will be described. Spectroscopic and reaction-dynamics experiments with these samples will be presented.

The large polarizability of atoms in highly excited states, so called Rydberg states, leads to strong and long-ranging interactions between such atoms. Interacting pairs of Rydberg atoms represent a very exotic molecular system, characterized by high internal excitation, high density of electronic states, internuclear separations exceeding one micrometer, and lifetimes beyond tens of microseconds. I will discuss the computational methods we have developed to determine the electronic structure of interacting Rydberg-atom pairs and our spectroscopic approaches to verify these calculations.