2019/03/27 by M. Hatridge, S. Shankar, M. Mirrahimi +9 · 2 citations
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1126/science.1226897
published as Science 11 Jan 2013: Vol. 339, Issue 6116, pp. 178-181
arxiv created 2019/03/27 · arxiv updated 2019/03/29
Measuring a quantum system can randomly perturb its state. The strength and nature of this back-action depends on the quantity which is measured. In a partial measurement performed by an ideal apparatus, quantum physics predicts that the system remains in a pure state whose evolution can be tracked perfectly from the measurement record. We demonstrate this property using a superconducting qubit dispersively coupled to a cavity traversed by a microwave signal. The back-action on the qubit state of a single measurement of both signal quadratures is observed and shown to produce a stochastic operation whose action is determined by the measurement result. This accurate monitoring of a qubit state is an essential prerequisite for measurement-based feedback control of quantum systems.