Every measurement of the population in an uncorrelated ensemble of two-levelsystems is limited by what is known as the quantum projection noise limit.Here, we present quantum projection noise limited performance of a Ramsey typeinterferometer using freely propagating coherent atoms. The experimental setupis based on an electro-optic modulator in an inherently stable Sagnacinterferometer, optically coupling the two interfering atomic states via atwo-photon Raman transition. Going beyond the quantum projection noise limitrequires the use of reduced quantum uncertainty (squeezed) states. Theexperiment described demonstrates atom interferometry at the fundamental noiselevel and allows the observation of possible squeezing effects in an atomlaser, potentially leading to improved sensitivity in atom interferometers.
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