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Title: Behavior of the maximum likelihood in quantum state tomography

Abstract

Quantum state tomography on a d-dimensional system demands resources that grow rapidly with d. They may be reduced by using model selection to tailor the number of parameters in the model (i.e., the size of the density matrix). Most model selection methods typically rely on a test statistic and a null theory that describes its behavior when two models are equally good. Here, we consider the loglikelihood ratio. Because of the positivity constraint ρ ≥ 0, quantum state space does not generally satisfy local asymptotic normality (LAN), meaning the classical null theory for the loglikelihood ratio (the Wilks theorem) should not be used. Thus, understanding and quantifying how positivity affects the null behavior of this test statistic is necessary for its use in model selection for state tomography. We define a new generalization of LAN, metric-projected LAN, show that quantum state space satisfies it, and derive a replacement for the Wilks theorem. In addition to enabling reliable model selection, our results shed more light on the qualitative effects of the positivity constraint on state tomography.

Authors:
 [1]; ORCiD logo [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Univ. of New Mexico, Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1335564
Report Number(s):
SAND-2016-8677J
Journal ID: ISSN 1367-2630; 647145
DOE Contract Number:  
NA0003525
Resource Type:
Journal Article
Resource Relation:
Journal Name: New Journal of Physics; Journal Volume: 20
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS

Citation Formats

Blume-Kohout, Robin J, and Scholten, Travis L. Behavior of the maximum likelihood in quantum state tomography. United States: N. p., 2018. Web. doi:10.1088/1367-2630/aaa7e2.
Blume-Kohout, Robin J, & Scholten, Travis L. Behavior of the maximum likelihood in quantum state tomography. United States. doi:10.1088/1367-2630/aaa7e2.
Blume-Kohout, Robin J, and Scholten, Travis L. Thu . "Behavior of the maximum likelihood in quantum state tomography". United States. doi:10.1088/1367-2630/aaa7e2. https://www.osti.gov/servlets/purl/1335564.
@article{osti_1335564,
title = {Behavior of the maximum likelihood in quantum state tomography},
author = {Blume-Kohout, Robin J and Scholten, Travis L.},
abstractNote = {Quantum state tomography on a d-dimensional system demands resources that grow rapidly with d. They may be reduced by using model selection to tailor the number of parameters in the model (i.e., the size of the density matrix). Most model selection methods typically rely on a test statistic and a null theory that describes its behavior when two models are equally good. Here, we consider the loglikelihood ratio. Because of the positivity constraint ρ ≥ 0, quantum state space does not generally satisfy local asymptotic normality (LAN), meaning the classical null theory for the loglikelihood ratio (the Wilks theorem) should not be used. Thus, understanding and quantifying how positivity affects the null behavior of this test statistic is necessary for its use in model selection for state tomography. We define a new generalization of LAN, metric-projected LAN, show that quantum state space satisfies it, and derive a replacement for the Wilks theorem. In addition to enabling reliable model selection, our results shed more light on the qualitative effects of the positivity constraint on state tomography.},
doi = {10.1088/1367-2630/aaa7e2},
journal = {New Journal of Physics},
number = ,
volume = 20,
place = {United States},
year = {Thu Feb 22 00:00:00 EST 2018},
month = {Thu Feb 22 00:00:00 EST 2018}
}