Quantum Magnetometry

Towards Heisenberg Limit in Magnetometry with Parametric Down-converted Photons

In this paper, [DOI: 10.1103/PhysRevA.74.053810] we present an analysis of how parametric down converted photons could be useful in getting better spectroscopic information about the medium. We demonstrate how the improvement in magneto-optical rotation (MOR) of light could be realized by employing non-collinear down conversion geometry as shown in Fig. 1. We calculate the resolution that can be achieved in the MOR's both by use of coherent light and down converted light. The sensitivity depends on whether the two-photon or four-photon coincidence detection is used. We show that four-photon coincidence detection by the use of non-collinear type-II PDC light in MOR's increases the sensitivity by a factor of four in compared to coherent light. We also give an argument that minimum rotation uncertainty scales to Heisenberg limit by the use of down converted photons. Our results apply to sources with arbitrary pumping of the nonlinear crystal which is used in the production of PDC photons.