### Abstract

I consider the tradeoff between the information gained about an initially unknown quantum state, and the disturbance caused to that state by the measurement process. I show that for any distribution of initial states, the information-disturbance frontier is convex, and disturbance is nondecreasing with information gain. I consider the most general model of quantum measurements, and all post-measurement dynamics compatible with a given measurement. For the uniform initial distribution over states, I show that an optimal information-disturbance combination may always be achieved by a measurement procedure which satisfies a generalization of the projection postulate, the ``square-root dynamics.'' I use this to show that the information-disturbance frontier for the uniform ensemble may be achieved with ``isotropic'' (unitarily covariant) dynamics. This results in a significant simplification of the optimization problem for calulating the tradeoff in this case, giving hope for a closed-form solution. Some of the results also apply to certain discrete ensembles relevant to quantum cryptography.

Translated title of the contribution | Information-disturbance tradeoff in quantum measurement on the uniform ensemble |
---|---|

Original language | English |

Publisher | Department of Computer Science, University of Bristol |

Publication status | Published - 2000 |

### Bibliographical note

Other page information: -32Other identifier: 1000496

## Fingerprint Dive into the research topics of 'Information-disturbance tradeoff in quantum measurement on the uniform ensemble'. Together they form a unique fingerprint.

## Cite this

Barnum, H. (2000).

*Information-disturbance tradeoff in quantum measurement on the uniform ensemble*. Department of Computer Science, University of Bristol. http://www.cs.bris.ac.uk/Publications/pub_master.jsp?id=1000496