  We demonstrate a scheme for realizing a compact cold atom gravimeter. The use
of a hollow pyramidal configuration allows to achieve all functions: trapping,
interferometer and detection with a unique laser beam leading to a drastic
reduction in complexity and volume. In particular, we demonstrate a relative
sensitivity to acceleration of gravity (g) of 1.7 x 10-7 at one second, with a
moderate laser power of 50 mW. This simple geometry combined to such a high
sensitivity opens wide perspectives for practical applications (P. Bouyer and
A. Landragin, patent number FR2009/000252, 2009).
