project_state_matrix_to_physical

forest.benchmarking.operator_tools.project_state_matrix.project_state_matrix_to_physical(rho: numpy.ndarray) → numpy.ndarray

Project a possibly unphysical estimated density matrix to the closest (with respect to the 2-norm) positive semi-definite matrix with trace 1, that is a valid quantum state.

This comes from the so called “wizard” method. It is described in [MLEWIZ]

[MLEWIZ]

Efficient Method for Computing the Maximum-Likelihood Quantum State from Measurements with Additive Gaussian Noise. Smolin et al. Phys. Rev. Lett. 108, 070502 (2012). https://doi.org/10.1103/PhysRevLett.108.070502 https://arxiv.org/abs/1106.5458

Parameters:rho – the density (state) matrix with shape (N, N) Return rho_projected:  The closest positive semi-definite trace 1 matrix to rho.