Conservation law induced limitations to quantum measurements

Speaker: 
Leon Loveridge (University of York/ UK)
Event Date and Time: 
Mon, 2012-02-27 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Robert Raussendorf
Intended Audience: 
Graduate
The theorem of Wigner, Araki and Yanase (WAY) demonstrates that there are constraints to quantum measurements when there is an additive conserved quantity (on the Hilbert space of the system and measuring apparatus) that does not commute with the observable we wish to measure. The original theorem applied only to a restricted class of observables and conserved quantities. I'll review this theorem and its role in quantum information/computation and discuss some recent generalisations, in particular to the case of position measurements which respect the conservation of linear momentum. I'll also talk about various options for circumventing the constraints imposed by the WAY theorem, for example via a notion of ``relative observables'', which links with the subject of quantum reference frames.
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