Introduction

The cold atom gyroscope-accelerometer, developed at SYRTE laboratory, has demonstrated the possibility of measuring the full base of inertia (three components of rotation and three components of acceleration) within the same apparatus. It is based on atom interferometry technics, in which the atomic wave-packets are splitted and recombined thanks to laser beams. The two partial atomic wave-packets associated to each atom follows two different paths in the same time as optical waves in an optical interferometer.

3 pulse configuration

This interferometer is sensitive to the acceleration along the direction of propagation of the lasers and to rotation component along the normal to the oriented area. The sensitivity to rotation is well known in optics as the Sagnac effect, which is proportional to the surface included inside the two arms of the interferometer. The use of two atomic sources, launched in opposite directions, enables to discriminate between rotation and acceleration signals. Thanks to the used of cold atoms, cooled down to 1 µK with optical molasses, and using laser beams propagating in the three orthogonal directions, we have successively access to the three components of rotation and acceleration.

Interferometer fringe paterns for the two atomic sources

Interference fringes obtained with the two sources in configuration with vertical laser beams. The contrast is about 30%.

The performances are similar to these of standard technologies: mechanical accelerometer and optical gyroscopes. In one second of measurement time, the sensitivity to accelerations is one part of twenty million of the Earth’s gravity (5.10^-7 m.s^-2) and the sensitivity to rotation is one of three hundred of the earth’s rotation rate (2.4 10^-7 rad.s^-1). Moreover, one of the interest of the atomic sensors comes from there ability to improve in sensitivity by averaging the signal during long period of time (few days), which is needed for expected applications: in inertial navigation, in geophysics (rotation of the Earth and gravimetry) and in fundamental physics (specially test of the relativity). Ongoing studies aims to identify and push the limits of such interferometers, which are linked to the understanding and the control of the atom-laser interactions during the manipulations of the atomic wave-packets.

4 pulse configuration

Diagram of the 4 pulse interferometer

Diagram of a 4 pulse interferometer sensitive only to rotation.

We demonstrated the possibility of measuring rotation rate with a sequence of four pulses, giving access to the component of rotation along the direction of launching of the atoms (Ω_x), which is not accessible with the configuration with three pulses. This interferometer is no more sensitive to acceleration but only to rotation.

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