Precision Rotation Measurements with an Atom Interferometer Gyroscope

Matter-wave interferometry has the potential to be an extremely sensitive probe for inertial forces. For example, neutron interferometers have been used to measure the rotation of the Earth [1] and the acceleration due to gravity [2]. More recently, atom interference techniques have been used in demonstration experiments to measure rotations [3] and accelerations [4]. In this Letter, we present an atom-based Sagnac gyroscope that has a shortterm sensitivity comparable to state-of-the-art optical gyroscopes [5,6], and is at least 2 orders of magnitude better than previous matter-based experiments [1,3,7]. In the Sagnac geometry [8], rotation induces a phase shift Df between two interfering propagation paths. For a Sagnac loop enclosing area A, a rotation V produces a shift Df ­ 4p ly V ? A, where l is the particle wavelength and y its velocity [9–11]. Thus the inherent sensitivity of a matter-wave gyroscope exceeds that of a photonbased system by a factor of mc2yh̄v ,1011 (m is the particle mass, v the photon frequency). Although optical gyroscopes have higher particle fluxes and larger enclosed areas, atom-based systems should still out-perform optical systems by several orders of magnitude. Higher precision gyroscopes could find practical applications in navigation or in geophysical studies. They could also be used in tests of general relativity [6,12,13]. For example, one might realize a ground-based detection of the dragging of inertial frames [14]. We have developed an atomic state interferometer [15] which uses two-photon velocity selective Raman transitions [16,17] to manipulate atoms while keeping them in long-lived ground states. With the Raman method, two laser beams of frequency v1 and v2 are tuned to be nearly resonant with an allowed optical transition. Their frequency difference v1 2 v2 is chosen to be resonant with a microwave transition between two atomic ground-state levels. Under appropriate conditions, the atomic population Rabi flops between the ground-state levels with a rate proportional to the product of the two single-photon Rabi frequencies and inversely proportional to the optical detuning. When the beams are aligned to counterpropagate, a momentum exchange of approximately twice the singlephoton momentum accompanies these transitions. This leads to a strong Doppler sensitivity of the two-photon