Quantum state tomography of photons polarization and path degrees of freedom

Abstract

Quantum state tomography (QST), the process through which the density matrix of a quantum system is characterized from measurements of specific observables, is a fundamental pillar in the fields of quantum information and computation. We propose a simple QST method to reconstruct the density matrix of two qubits encoded in the polarization and path degrees of freedom of a single photon, which can be realized with a single linear-optical setup. We demonstrate that the density matrix can be fully described in terms of the one-point Stokes parameters related to the two possibles paths of the photon, together with a quantum version of the two-point Stokes parameters introduced here.Comment: 5 pages, 2 figure