Measurement-based Quantum Computing with Superconducting Charge Qubits RIKEN Wang, You and Nori report on measurement-based preparation of superconducting cluster states. "The measurement of the current of a few parallel Josephson-junction qubits realizes a novel type of quantum-state selector. Using this selector, one can produce various quantum entangled states and also realize a controlled-NOT gate without requiring an exact control of the interqubit interactions. In particular, cluster states for quantum computation could be produced with only single-qubit measurements."
Measuring the Size of a Schrödinger Cat State München "We propose a measure for the "size" of a Schrödinger cat state, i.e. a quantum superposition of two many-body states with macroscopically distinct properties, by counting how many single-particle operations are needed to map one state onto the other. This definition gives sensible results for simple, analytically tractable cases and is consistent with a previous definition restricted to Greenberger-Horne-Zeilinger-like states. We apply our measure to the experimentally relevant, nontrivial example of a superconducting three-junction flux qubit put into a superposition of left- and right-circulating supercurrent states and find this Schroedinger cat to be surprisingly small."
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