Daniel Oblak – Niels Bohr Institute - University of Copenhagen

Daniel Oblak

Title: Quantum State Engineering in Cold Caesium Atoms

A thesis submitted December 21st, 2009 for the degree of Doctor of Philosophy and defended February 1st, 2010.

The Niels Bohr Institute, Danish National Research Foundation Centre for Quantum Optics, The Graduate School of Science, Faculty of Science, University of Copenhagen, Denmark.

Eugene S. Polzik

Carlos L. Garrido Alzar
Jörg H. Müller
Niels Kjærgaard
Anders S. Sørensen
Jürgen Appel

(67 Mb) Download Thesis >>


Quantum State Engineering in Cold Caesium Atoms

An entangled tale of non-destructively induced collapse and squeezing of atomic states.

Quantum mechanics is characterised by several strange features, which include quantum uncertainty, quantum measurements, and entanglement. This thesis involves all three of these. The quantum uncertainty poses a fundamental standard quantum limit (SQL) in applications where quantum systems are used to gauge some quantity. A prime example is that of atomic frequency standards, which with unprecedented precision measure an atomic quantum state. Quantum measurements in the form of Quantum Non-Demolition (QND) measurements can be engineered so as to overcome the SQL by redistributing quantum uncertainty amongst different variables of the system. Such squeezed spin-states rely on inter-atomic correlation, which goes by the name of entanglement.

In this work we present a detailed description of how we have implemented a QND measurement with laser pulses in a Mach-Zehnder Interferometer (MZI) and demonstrate that we can engineer a squeezed state in a cold trapped ensemble of Cs atoms. We verify that the squeezing is useful for improving the precision of atomic clocks. Along the way, we also investigate several remarkable features of the interaction, by which atoms and light-particles (photons) exchange phase-shifts.

(67 Mb) Download Thesis >>