Interferometry, the most precise measurement technique known today, exploits the wave-like nature of the atoms or photons in the interferometer. As expected from the laws of quantum mechanics, the granular, particle-like features of the individually independent atoms or photons are responsible for the precision limit, the shot noise limit. However this classical bound is not fundamental and it is the aim of quantum metrology to overcome it by employing entanglement among the particles. This work reports on the realization of spin-squeezed states suitable for atom interferometry. Spin squeezing was generated on the basis of motional and spin degrees of freedom, whereby the latter allowed the implementation of a full interferometer with quantum-enhanced precision.

Recipient of the German Physical Society's 2011 Dissertation Prize Important contribution to pushing back the precision limit in interferometry Provides excellent theoretical overview in addition to the experimental advances Includes supplementary material: sn.pub/extras

Inhalt
Introduction.- Spin Squeezing, Entanglement and Quantum Metrology.- Squeezing Two Mean Field Modes of a Bose-Einstein Condensate.- Non-linear Interferometry Beyond the Standard Quantum Limit.- Outlook. - Appendices.