David Holleville

Six-axis inertial sensor using cold-atom interferometry.

We have developed an atom interferometer providing a full inertial base. This device uses two counterpropagating cold-atom clouds that are launched in strongly curved parabolic trajectories. Three single Raman beam pairs, pulsed in time, are successively applied in three orthogonal directions leading to the measurement of the three axis of rotation and acceleration. In this purpose, we introduce a new atom gyroscope using a butterfly geometry. We discuss the present sensitivity and the possible improvements.

The BNM Watt balance project

A new watt balance project is now developed by the BNM: the general configuration and the main parts of the experimental set-up in development are presented. Its aim is to contribute to the international effort in monitoring the kilogram towards a new definition of the mass unit with an accuracy of 10-8 or better

Observation of Raman-Ramsey fringes with optical CPT pulses

The Ramsey method has been applied by means of optical coherent population trapping (CPT) pulses through a cesium vapor cell with N/sub 2/ buffer gas at room temperature, using two phase-locked lasers. With this method, CPT resonance spectral widths are no longer limited by optical saturation and collision effects, but only depend on free evolution time between the two pulses. A fringe width below 100 Hz is reported. Experimental Raman-Ramsey fringes are analyzed using the classical wavefunction formalism.

Influence of lasers propagation delay on the sensitivity of atom interferometers

Abstract.In atom interferometers based on two photon transitions, the delay induced by the difference of the laser beams paths makes the interferometer sensitive to the fluctuations of the frequency of the lasers. We first study, in the general case, how the laser frequency noise affects the performance of the interferometer measurement. Our calculations are compared with the measurements performed on our cold atom gravimeter based on stimulated Raman transitions. We finally extend this study to the case of cold atom gradiometers.

Reaching the quantum noise limit in a high-sensitivity cold-atom inertial sensor

In our high-precision atom interferometer, the measured atomic phase shift is sensitive to rotations and accelerations of the apparatus, and also to phase fluctuations of the Raman lasers. In this paper we study two principal noise sources affecting the atomic phase shift, induced by optical phase noise and vibrations of the setup. Phase noise is reduced by carrying out a phase lock of the Raman lasers after the amplification stages. We also present a new scheme to reduce noise due to accelerations by using a feed-forward on the phase of the Raman beams. With these methods, it should be possible to reach the range of the atomic quantum projection noise limit, which is about 1m rad rmsfor our experiment, i.e. 30 nrad s −1 Hz −1/2 for a rotation

Constructive polarization modulation for coherent population trapping clock

We propose a constructive polarization modulation scheme for atomic clocks based on coherent population trapping (CPT). In this scheme, the polarization of a bichromatic laser beam is modulated between two opposite circular polarizations to avoid trapping the atomic populations in the extreme Zeeman sublevels. We show that if an appropriate phase modulation between the two optical components of the bichromatic laser is applied synchronously, the two CPT dark states which are produced successively by the alternate polarizations add constructively. Measured CPT resonance contrasts up to 20% in one-pulse CPT and 12% in two-pulse Ramsey-CPT experiments are reported, demonstrating the potential of this scheme for applications to high performance atomic clocks.

Influence of optical aberrations in an atomic gyroscope

Abstract.In atom interferometry based on light-induced diffraction, the optical aberrations of the laser beam splitters are a dominant source of noise and systematic effect. In an atomic gyroscope, this effect is dramatically reduced by the use of two atomic sources. But it remains critical while coupled to fluctuations of atomic trajectories, and appears as a main source of noise to the long term stability. Therefore we measure these contributions in our set-up, using cold cesium atoms and stimulated Raman transitions.

Limitations to the short term frequency stability in a compact cold atom clock

The HORACE device is a compact cold atom clock where about 10/sup 8/ cesium atoms are laser cooled at a few /spl mu/K, then interrogated and detected directly in a 20 cm/sup 3/ spherical microwave cavity. The optimization of the short term stability with the cooling and interrogation durations is presented, leading to an estimation of the Allan deviation of /spl sigma//sub y/(/spl tau/) -1 10/sup -13/ /spl tau/ /sup - 1/2 /on earth and /spl sigma//sub y/(/spl tau/) = 7 10/sup -14/ /spl tau//sup -frac12;/ in space. The quantum projection noise, the Dick effect and the detection laser noises are taken into account. The calculations are based on a preliminary model for the recapture of cold atoms, in reasonable agreement with measurements.

Cold Atom Absolute Gravimeter for the Watt Balance

We are building a cold atom absolute gravimeter based on atom interferometry with a projected accuracy of 10-9 g. It is part of the French watt balance project intending to link the SI Kg unit to fundamental constants

A cold atom interferometer for high precision inertial measurements

The authors are developing a high precision inertial sensor. This device uses cold Caesium atoms manipulated by stimulated Raman transitions (Berman, 1997). As this setup is sensitive to both acceleration and rotation, two counter-propagating beams of cold atoms are used to discriminate between the two contributions. The last experimental results will be presented here