Coherent State Evolution in a Superconducting Qubit from Partial-Collapse Measurement
Nadav Y. Katz, M. Ansmann, Radoslaw C. Bialczak, Erik A. Lucero, R. McDermott, M. Neeley, Matthias Steffen, Eva Maria Weig, Andrew N. Cleland, John M. Martinis, Alexander N. Korotkov · Science · 2006
Measurement is one of the fundamental building blocks of quantum-information processing systems. Partial measurement, where full wavefunction collapse is not the only outcome, provides a detailed test of the measurement process. We introduce quantum-state tomography in a superconducting qubit that exhibits high-fidelity single-shot measurement. For the two probabilistic outcomes of partial measurement, we find either a full collapse or a coherent yet nonunitary evolution of the state. This latter behavior explicitly confirms modern quantum-measurement theory and may prove important for error-correction algorithms in quantum computation.