title: Reversal of the weak measurement of a quantum state in a superconducting phase qubit.
abstract: 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.
authors.affiliation: Department of Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: Nadav
authors.initials: N
authors.lastname: Katz
authors.forename: Matthew
authors.initials: M
authors.lastname: Neeley
authors.forename: M
authors.initials: M
authors.lastname: Ansmann
authors.forename: Radoslaw C
authors.initials: RC
authors.lastname: Bialczak
authors.forename: M
authors.initials: M
authors.lastname: Hofheinz
authors.forename: Erik
authors.initials: E
authors.lastname: Lucero
authors.forename: A
authors.initials: A
authors.lastname: O'Connell
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: A N
authors.initials: AN
authors.lastname: Cleland
authors.forename: John M
authors.initials: JM
authors.lastname: Martinis
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Korotkov