Quantum process tomography of a magneto-optic transformation

Abstract

We characterize a magneto-optic transformation in the Faraday modality via quantum process tomography (QPT) with quantum light comprising of antibunched single photons generated through heralded spontaneous parametric downconversion. We derive a general process matrix for a unitary transformation which effectively describes the action of the magneto-optic element. This matrix quantifies the polarization attributes of the single photon as it traverses through the magneto-optic element. The magnitude of rotation and ellipticity are extracted through a maximum likelihood based optimization of the process matrix. Measurements are performed for a wide range of temperatures (8–100 K) and applied magnetic fields. The estimated rotation angles are curve fit to determine the Curie-Weiss constant for a terbium gallium garnet crystal. The extracted angles are also utilized to map the rotations on the surface of Bloch sphere.