ATOMIC CAVITIES

We demonstrate an example of a conservative trap for neutral atoms; th is trap is a gravitational cavity, formed by a single concave atomic m irror formed using a laser evanescent wave. We present the principle o f this mirror and we show how it can be used to design atom optics dev ices. Using a sinusoidal modulation of the mirror, we demonstrate the phase modulation of the reflected de Broglie atomic waves. This techni que provides an efficient and flexible coherent atomic beam splitter f or applications in atom optics and atom interferometry.