Affiliation:
1. Paul Scherrer Institute
2. Laboratory for Solid State Physics
3. ICFO – Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology
Abstract
An optical waveplate rotating light polarization can be modeled as a single-qubit unitary operator. This analogy can be exploited to experimentally retrieve a polarization transformation within the paradigm of quantum process tomography. Standard approaches to tomographic problems rely on the maximum-likelihood estimation, providing the most likely transformation to yield the same outcomes as a set of experimental projective measurements. The performances of this method strongly depend on the number of input measurements and the numerical minimization routine that is adopted. Here we investigate the application of genetic and machine learning approaches to this problem, finding that both allow for accurate reconstructions and fast operations when processing a set of projective measurements very close to the minimal one. We apply these techniques to the case of space-dependent polarization transformations, providing an experimental characterization of the optical action of spin-orbit metasurfaces having patterned birefringence. Our efforts thus expand the toolbox of methodologies for optical process tomography. In particular, we find that the neural network-based scheme provides a significant speed-up, that may be critical in applications requiring a characterization in real-time. We expect these results to lay the groundwork for the optimization of tomographic approaches in more general quantum processes, including non-unitary gates and operations in higher-dimensional Hilbert spaces.
Funder
'la Caixa' Foundation
Marie-Sklodowska-Curie
Narodowe Centrum Nauki
EU Horizon
Barcelona Supercomputing Center
European Social Fund
Fundació Mir-Puig
Fundació Cellex
European Union NextGenerationEU
Ministerio de Ciencia y Innovation Agencia Estatal de Investigaciones
European Research Council
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Ministero dell'Università e della Ricerca
Subject
Atomic and Molecular Physics, and Optics