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arXiv · 1903.11732

Quantum back-action of variable-strength measurement

M. Hatridge·S. Shankar·M. Mirrahimi·F. Schackert·K. Geerlings·T. Brecht·K. M. Sliwa·B. Abdo·L. Frunzio·S. M. Girvin·R. J. Schoelkopf·M. H. Devoret
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Abstract

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.

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M. Hatridge, S. Shankar, M. Mirrahimi, F. Schackert, K. Geerlings, T. Brecht, K. M. Sliwa, B. Abdo, L. Frunzio, S. M. Girvin, R. J. Schoelkopf, M. H. Devoret. 2019-03-27. Quantum back-action of variable-strength measurement. https://doi.org/10.1126/science.1226897

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