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Quantum-enhanced magnetometry and nonlinear metrology with atomic ensembles.

Morgan Mitchell, Institute of Photonic Sciences

(Session 5 : Friday from 4:00pm-4:45pm)

Abstract. I will present recent results on quantum metrology combining atomic and quantum-optical systems. Optical magnetometry, which employs an atomic ensemble interacting with an optical beam, is both of considerable practical interest and a good test-bed for quantum metrology with dual quantum systems. With a hot atomic ensemble, we have recently demonstrated a squeezed-light-enhanced rubidium magnetometer, showing the possibility of sub-shot-noise performance in this system. I will also describe an analogous cold atom system which achieves both shot-noise- and projection-noise-limited performance, allowing study of optical magnetometry in a fully-quantum regime. We have recently pushed this cold-atom quantum interface into the nonlinear regime, using spin-dependent optical nonlinearities to perform shot-noise-limited measurements of the ensemble spin. By implementing a non-linear Hamiltonian proposed by Boixo et al. [Phys. Rev. Lett. 101, 040403 (2008)], we demonstrate a sensitivity scaling better than the 1/N "Heisenberg limit" over two orders of magnitude in photon number.