Certified quantum non-demolition measurement of material
systems
Morgan W. Mitchell,1, 2 Marco Koschorreck,3
Marcin Kubasik,4 Mario Napolitano,1 and Robert J. Sewell1
1ICFO – Institut de Ciencies Fotoniques, Av. Carl
Friedrich Gauss, 3, 08860 Castelldefels, Barcelona, Spain
2ICREA – Instituci´o Catalana de Recerca i Estudis Avan¸cats, 08015 Barcelona, Spain
3Cavendish Laboratory, University of Cambridge,
JJ Thomson Avenue, Cambridge CB3 0HE, UK
4Optos, Carnegie Campus, Dunfermline, KY11 8GR, Scotland, UK
Abstract
An extensive debate on quantum non-demolition (QND) measurement, reviewed in Grangier et
al. [Nature, 396, 537 (1998)], finds that true QND measurements must have both non-classical
state-preparation capability and non-classical information-damage tradeoff. Existing figures of
merit for these non-classicality criteria require direct measurement of the signal variable and are
thus difficult to apply to optically-probed material systems. Here we describe a method to demonstrate
both criteria without need for to direct signal measurements. Using a covariance matrix
formalism and a general noise model, we compute meter observables for QND measurement triples,
which suffice to compute all QND figures of merit. The result will allow certified QND measurement
of atomic spin ensembles using existing techniques.
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