Abstract
We discuss the problem of estimating a qubit mixed state. We give the optimal estimation that can be inferred from any given set of measurements. For collective measurements and for a large number N of copies, we show that the error in the estimation varies as For local measurements, we focus on the simpler case of states lying on the equatorial plane of the Bloch sphere. We show that the error using plain tomography varies as while our approach leads to an error proportional to
- Received 17 September 2003
DOI:https://doi.org/10.1103/PhysRevA.69.010304
©2004 American Physical Society