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Two distinct methods for measuring topological charge in a nonabelian anyonic system have been discussed in the literature: projective measurement of a single point-like quasiparticle and interferometric measurement of the total topological charge of a group of quasiparticles. Projective measurement by definition is only applied near a point and will project to a topological charge sector near that point. Thus, if it is to be applied to a group of anyons to project to a total charge, then the anyons must first be fused one by one to obtain a single anyon carrying the collective charge. We show that interferometric measurement is strictly stronger: Any protocol involving projective measurement can be simulated at low overhead by another protocol involving only interferometric measurement.
@InProceedings{levaillant_et_al:LIPIcs.TQC.2015.245,
author = {Levaillant, Claire and Freedman, Michael},
title = {{Interferometric Versus Projective Measurement of Anyons}},
booktitle = {10th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2015)},
pages = {245--249},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-96-5},
ISSN = {1868-8969},
year = {2015},
volume = {44},
editor = {Beigi, Salman and K\"{o}nig, Robert},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TQC.2015.245},
URN = {urn:nbn:de:0030-drops-55600},
doi = {10.4230/LIPIcs.TQC.2015.245},
annote = {Keywords: anyons, measurement, interferometry, physics}
}