Low Temperature Decoherence and Relaxation in Charge Josephson Junction Qubits

Research interest in controllable two-level systems, which have been enthusiastically called quantum bits or qubits, has grown enormously during the last decade. Behind a huge burst of activity in this field stands an idea of what is possible in principle but extremely difficult to achieve instrumentally - the fascinating idea of quantum computing. The very principle of quantum superposition allows many operations to be performed on a quantum computer in parallel, while an ordinary ‘classical’ computer, however fast, can only handle one operation at a time. The enthusiasm is not held back by the fact that exploiting quantum parallelism is by no means straightforward, and there exist only a few algorithms (e.g., [1, 2]) for which the quantum computer (if ever built) would offer an essential improvement in comparison with its ‘classical’ counterpart. Even if other uses of quantum computing prove limited (which might or might not be the case), its existence would most certainly lead to a breakthrough in simulations of real physical many-particle systems.