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Phys. Rev. Lett. 101, 200401 (2008) [4 pages]

Reversal of the Weak Measurement of a Quantum State in a Superconducting Phase Qubit

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Nadav Katz1,*, Matthew Neeley1, M. Ansmann1, Radoslaw C. Bialczak1, M. Hofheinz1, Erik Lucero1, A. O’Connell1, H. Wang1, A. N. Cleland1, John M. Martinis1, and Alexander N. Korotkov2
1Department of Physics, University of California, Santa Barbara, California 93106, USA
2Department of Electrical Engineering, University of California, Riverside, California 92521, USA

Received 11 June 2008; published 10 November 2008

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We demonstrate in a superconducting qubit the conditional recovery (uncollapsing) of a quantum state after a partial-collapse measurement. A weak measurement extracts information and results in a nonunitary transformation of the qubit state. However, by adding a rotation and a second partial measurement with the same strength, we erase the extracted information, canceling the effect of both measurements. The fidelity of the state recovery is measured using quantum process tomography and found to be above 70% for partial-collapse strength less than 0.6.

© 2008 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.101.200401
DOI:
10.1103/PhysRevLett.101.200401
PACS:
03.65.Ta, 03.67.Lx, 85.25.Cp

*Current address: The Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel.

 
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