Estimating the expectation values of spin-1/2 observables with finite resources

Thomas Brougham, Erika Andersson

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We examine the problem of estimating the expectation values of two observables when we have a finite number of copies of an unknown qubit state. Specifically we examine whether it is better to measure each of the observables separately on different copies or to perform a separable nonadaptive joint measurement of the observables on each copy. We find that joint measurements can sometimes provide an advantage over separate measurements, but only if we make estimates of an observable based solely on the results of measurements of that observable. If we instead use both sets of results to estimate each observable then we find that individual measurements will be better. Finally we consider estimating the expectation values of three complementary observables for an unknown qubit.

Original languageEnglish
Article number052313
Number of pages10
JournalPhysical Review A
Issue number5
Publication statusPublished - Nov 2007


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