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.
- Received 11 June 2008
DOI:https://doi.org/10.1103/PhysRevLett.101.200401
©2008 American Physical Society
Viewpoint
Undoing a quantum measurement
Published 10 November 2008
Quantum measurements are conventionally thought of as irretrievably “collapsing” a wave function to the observed state. However, experiments with superconducting qubits show that the partial collapse resulting from a weak continuous measurement can be restored.
See more in Physics