Patrick Joachim Windpassinger

Title: Non-destructive quantum state measurements and Quantum noise squeezing

A Ph.D. Thesis submitted October 20, 2008

Danish National Research Foundation Center for Quantum Optics (QUANTOP) - Niels Bohr Institute, Faculty of Science, University of Copenhagen October 2008

Academic supervisors: Prof. Eugene S. Polzik
Assoc. Research Prof. Niels Kjærgaard

Evaluation committee:
NBI local head: Prof. Andrew Jackson

External referees:
Prof. Elisabeth Giacobino
Prof. Dieter Meschede

Abstract

Non-destructive quantum state measurements and Quantum noise squeezing

A method for non-destructive probing of the clock state population of laser-cooled, dipole trapped Cs atoms at the standard quantum limit is presented.

The non-destructive probing allows us to follow the evolution of the population difference of the Cs-atom clock states when subjected to microwave fields in real time. This way, Rabi oscillations on the clock transition can be observed non-destructively over an extended period of time. We apply microwave spectroscopy techniques to characterize the evolution of the quantum state in the trap and especially focus on the  effect of probe induced inhomogeneous dephasing and of probe induced spontaneous photon scattering on the atomic ensemble.

We push the population readout precision to the quantum mechanical limits and demonstrate that the measurement precision is limited by quantum noise. We demonstrate that the correlations between two consecutive, non--destructive measurements are non--classical and that therefore an entangled state of atoms has been created in the ensemble. The correlations allow us to infer a quantum noise reduction of 72%, i.e., -5.4dB of remaining noise and -3.5dB of spectroscopically relevant quantum noise squeezing.