Quantum state tomography of photon's polarization and path degrees of freedom

TL;DR

This paper introduces a straightforward quantum state tomography method for two qubits encoded in a single photon's polarization and path, utilizing a linear-optical setup to reconstruct the density matrix via Stokes parameters.

Contribution

It presents a novel, simplified QST approach for photonic qubits using polarization and path degrees of freedom with a single optical setup.

Findings

Complete density matrix reconstruction using Stokes parameters.

Implementation of a quantum version of two-point Stokes parameters.

Photonic circuits for studying open quantum system dynamics.

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. In this work, 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 Stokes parameters related to the two possibles paths of the photon, together with a quantum version of the two-point Stokes parameters introduced here. Our findings put forward photonic circuits for the investigation of the dynamics of open quantum systems.