Phase variance of squeezed vacuum states
Bagán Capella, Emili (Universitat Autònoma de Barcelona. Departament de Física)
Monras Blasi, Àlex (University of Leeds. The School of Physics and Astronomy)
Muñoz Tapia, Ramon (Universitat Autònoma de Barcelona. Departament de Física)
American Physical Society

Date:	2008
Abstract:	We consider the problem of estimating the phase of squeezed vacuum states within a Bayesian framework. We derive bounds on the average Holevo variance for an arbitrary number N of uncorrelated copies. We find that it scales with the mean photon number n, as dictated by the Heisenberg limit, i. e. , as n−2, only for N>4. For N 4 this fundamental scaling breaks down and it becomes n−N/2. Thus, a single squeezed vacuum state performs worse than a single coherent state with the same energy. We find the optimal splitting of a fixed given energy among various copies. We also compute the variance for repeated individual measurements (without classical communication or adaptivity) and find that the standard Heisenberg-limited scaling n−2 is recovered for large samples.
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Published in:	Physical review. A, Vol. 78, Issue 4 (October 2008) , p. 043829-1-043829-7, ISSN 1050-2947

DOI: 10.1103/PhysRevA.78.043829

7 p, 149.9 KB

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