Cold atoms, quantum non demolition measurements, and squeezing in a high finesse optical cavity

Andréa D Bertoldi, Thomas Vanderbruggen, Simon Bernon +4 more

Thomas Vanderbruggen, Simon Bernon, Andréa D Bertoldi +2 more

Simon Bernon

This thesis investigates the generation of atomic spin-squeezed states by quantum non-demolition (QND) measurements in a high-finesse optical cavity. Cold atom interferometry has demonstrated state of the art performance for the measurement of tiny rotations, accelerations and time. The sensitivity of atom interferometers has already reached the atomic shot noise level, a limit that could be overcome by the use of non-classical atomic states. In this context, we developed a crossed high-finesse cavity resonating both at 1560 nm and 780 nm. Laser light at 1560 nm injected in the cavity generates a far off resonance optical dipole trap where Rb 87 cold atoms are loaded from a magneto-optical trap. The lifetime of the atoms in this dipole trap is limited by the residual background collisions, indicating that further evaporation process should be effective. The concepts of QND measurement are introduced and a wavefunction formalism that describes the spin-squeezing dynamics of the atomic state is discussed. This formalism is applied to practical measurement apparatus that are the Mach-Zehnder interferometer and the heterodyne detection. Experimentally, this non-destructive measurement was implemented at 780 nm in a frequency modulation scheme strongly immune to noise. The influence of this non-demolition probe on the atomic sample has been characterized in single pass and this tool has been applied to follow in real time the state of atomic interferometers. In addition to this work, a narrow linewidth Raman laser suitable for high precision spectroscopy was implemented with cold atoms as the gain medium.

Andréa D Bertoldi, Simon Bernon, Thomas Vanderbruggen +3 more

Simon Bernon, Thomas Vanderbruggen, Andréa D Bertoldi +4 more

Simon Bernon, Thomas Vanderbruggen, Ralf Kohlhaas +3 more

We report on a novel experiment to generate non-classical atomic states via quantum non-demolition (QND) measurements on cold atomic samples prepared in a high-finesse ring cavity. The heterodyne technique developed for QND detection exhibits an optical shot-noise limited behavior for local oscillator optical power of a few hundred μW, and a detection bandwidth of several GHz. This detection tool is used in a single pass to follow non-destructively the internal state evolution of an atomic sample when subjected to Rabi oscillations or a spin-echo interferometric sequence.