Quantum information processing with trapped 43Ca+ ions

The basic distinguishing feature of a quantum computer is its ability to utilize the parallelism inherent in quantum mechanics, thus potentially performing many operations simultaneously, while any classical computer relies on sequential processing of information. Furthermore, the computational power of a quantum computer grows exponentially with the size of the computer (the number of available "quantum bits"), and its quantum algorithms enable the efficient realization of classically intractable calculations, like the simulation of the behaviour of quantum systems or the factorization of large numbers. Since most data encryption techniques rely on the inability to perform the latter, mature quantum computing have a profound impact on a field that pervades our modern world. A quantum computer requires a system in which quantum bits interact strongly with each other, but not with the environment. In practice, this is a serious challenge. The large the size of the computer, the harder it is to avoid the dissipation of quantum information into the environment, a process called "decoherence". One of the most promising experimental approaches is that of a trapped-ion quantum computer. The idea is to represent quantum bits by the electronic state of individual ions that are trapped and localized in a radio frequency field in a vacuum environment. The ions can interact with each other via their shared oscillatory motion in the trap, and lasers are used to manipulate the electronic states of the ions. In the proposed experiment a string of 43Ca+ ions is trapped and the quantum information is stored in atomic states that are particularly resistant against decoherence. The ions can be individually addressed by a focused laser beam, and their atomic state is "ready out" by recording fluorescence light with a CCD camea. The goal of this research project is to combine new ideas and the best features of today`s ion trap experiments in order to push the frontiers of ion-trap based quantum computing. In particular, research will be focused on characterizing and combatting decoherence and exploring the scalability of such a system