Thermalisation and Controllability of Quantum Systems

Over the last decade we have seen an important paradigm shift in Quantum Mechanics. Whereas formerly the Heisenberg uncertainty principle was regarded as type of fundamental noise, it has now been accepted that the indecisiveness of Quantum Mechanics, with Schrdingers cat as a characteristic example, can actually be very useful to build powerful Quantum Computers.While the fundamental theory of Quantum Computation is quite developed, the field still lacks experimental confirmation of these concepts. The reason why it is so hard to perform experiments is that we are trying to connect the tiny quantum objects to our clumsy macroscopic world. One requires a large amount of control to run an algorithm on a Quantum Computer - it is as if we were playing piano with boxing gloves.My research is based on the relationship between control and noise. Generally control implies noise, i.e. the disturbance of the system, but strangly I have also found that noise can imply control! These counterintuitive results show that a deeper understanding of the fundamental forms of quantum mechanical noise is very useful to build a Quantum Computer. In the extrem case, I suggest methods where no external control is required at all, and the computer just runs like a mechanical clockwork. The proposed research is mostly concerned with the intermediate case, where the control is minimised under the relevant constraints, and the quantum noise is made use of in an optimal manner. One important aspect of it will be to develop experiments to test these concepts and to progress on the path to a full quantum computer. Another vital point will be to deepen the understanding of noise and of the relaxation of quantum systems from an information theory point of view. While everyone has a basic idea of what temperature means and how quantify energy, it turns out that on a quantum mechanical level these concepts are no longer well-defined. My research will contribute to this topic by developing toy-models and thought experiments to clarify such problems.