# Quantum metrology with a scanning probe atom interferometer

Ockeloen, Caspar Frederik. Quantum metrology with a scanning probe atom interferometer. 2014, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_10832

Atom interferometers provide record precision in measurements of a broad range of physical quantities. Extending atom interferometry to micrometer spatial resolution would enable new applications in electromagnetic field sensing, surface science, and the search for fundamental short-range interactions. I present experiments where we use a small Bose-Einstein condensate on an atom chip as an interferometric scanning probe to map out a microwave field at distances down to $16$ micrometer from the chip surface with a few micrometers spatial resolution. By creating entanglement between the atoms, our interferometer overcomes the standard quantum limit of interferometry by 4 dB in variance and maintains enhanced performance for interrogation times up to 10 ms. This corresponds to a microwave magnetic field sensitivity of 77 pT/sqrt(Hz) in a probe volume of 20 cubic micrometer. High-resolution measurements of microwave near-fields, as demonstrated here, are important for the development of integrated microwave circuits for quantum information processing and applications in communication technology.