Heng ShenHeng Shen

A thesis submitted December 2014 for the degree of Doctor of Philosophy and defended January 21, 2015.

The PhD School of Science
Faculty of Science, Niels Bohr Institute, Quantop, University of Copenhagen Denmark

Academic supervisor:
Prof. Eugene S. Polzik

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Spin squeezing and entanglement with room temperature atoms for quantum sensing and communication
In this thesis, different experiments on spin squeezing and entanglement involving room temperature ensembles of Cesium atoms are described. The key method is the off-resonant Faraday interaction of spin-polarized atomic ensemble with a light field. And the key component is the micro-fabricated vapor cell coupled into an optical cavity.

Quantum backaction evading measurement of one quadrature of collective spin components by stroboscopically modulating the intensity of probe beam at twice Larmor frequency is used to generate the spin-squeezed state. A projection noise limited optical magnetometer at room temperature is reported. Furthermore, using spin-squeezing of atomic ensemble, the sensitivity of magnetometer is improved.

Deterministic continuous variable teleportation between two distant atomic ensembles is demonstrated. The fidelity of teleportating dynamically changing sequence of spin states surpasses a classical benchmark, demonstrating the true quantum teleportation.

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