1/f noise and two-level systems in josephson qubits

Quantum state engineering in solid-state systems is one of the most rapidly developing areas of research. Solid-state building blocks of quantum computers have the advantages that they can be switched quickly, and they can be integrated into electronic control and measuring circuits. Substantial progress has been achieved with superconducting circuits (qubits) based on Josephson junctions. Strong coupling to the external circuits and other parts of the environment brings, together with the advantages, the problem of noise and, thus, decoherence. Therefore, the study of sources of decoherence is necessary. Josephson qubits themselves are very useful in this study: they have found their first application as sensitive spectrometers of the surrounding noise.