Quantum superposition of magnetic flux states in a superconducting loop

Results of the recent experiments have clear and convincingly demonstrated that superconducting circuits with certain parameters can be in quantum superposition of macroscopically distinct states. This has important implications, for instance, for the quantum measurement theory, for the description of the interaction between light and matter as well as for implementation of new generation of quantum limited detectors and quantum information processing devices. Here both – basic ideas and practical realization of superconducting qubits - are discussed.