Matterwave interferometry for inertial sensing

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Navigation is a difficult problem, especially when access to the skies is restricted. Currently, most international travel by plane and ship relies on location through the GPS (Global Positioning Signal) signal, which is provided by a fleet of 24 satellites in orbit around Earth. If this signal is lost then, much like ancient sailors without sight of the stars, then the traveller very quickly loses track of their position. Given that GPS is owned and operated by one country, the USA, who can switch it off at any time and, furthermore, that it is open to hacking, it is clear that a means to have completely independent knowledge of location is required. The aim of this project is generate purely passive methods of tracking position with better than state-of-the-art sensitivity by the using of newly developed tools from atomic physics that harness the state-of-the-art in precision measurement. Atoms are strongly affected by inertial forces, the "pushing" effect that is felt when suddenly accelerating. This effect is already used to measure gravity, where measuring the time it takes for an object to fall a certain distance allows us to detect the force exerted by the mass of the Earth. Huge advances have been made in laser physics the last decades that allow measurement of positions with sub-atomic resolution through optical interferometry, which allows for similar increases in sensitivity to measurement of forces. The solution then is to use the well-known laws of Newton to integrate back the instantaneous velocity and position. However, the sensitivity required is extremely strict - an error of 10-5 m/s2 (one millionth of the acceleration due to gravity) results in a drift in position of 100 m in just one hour, and of approximately 50 km in one day. The solution is to use a quantum technology; the matter-wave interferometer. The ability to cool atoms down to only a few micronK using laser light has enabled some of the most spectacular developments in atomic physics in recent years. One of the most profound is the direct observation of the de Broglie wave nature of atoms and the subsequent achievement of a Bose-Einstein condensate (BEC), a state of matter where a cloud of atoms coalesce into a single quantum state [1]. The possibility of using interference of these coherent matter waves offers new levels of potential accuracy for measurement devices. A particular application of interest is that of inertial sensing with applications in quantum-based autonomous navigation devices. The Experimental Quantum Optics and Photonics group within the Physics Department at the University of Strathclyde have been leading in research in this area and have demonstrated new different methods for atom interferometry. In fact, members of this group produced the first BEC in the UK also the first in Scotland. This project will build on existing research at Strathclyde University in atom interferometry with coherent matter waves and work on ring-shaped guided traps to explore the possibilities for developing miniaturised technology for rotation sensing. Central for this will be integration with Strathclyde's microfabrication technology [2], which was recently developed for miniaturisation of the optical set-up for laser cooling setup.The goal of the project will be the demonstration of a matter-wave Sagnac interferometer in a ring-trap geometry. The system of a coherent matter wave confined in a ring trap is formally equivalent to the coherent optical field (laser) in a ring cavity known from the ring laser gyro [3]. The interesting difference, though, is that the sensitivity to phase rotation scales with the relativistic energy of the particle/wave involved. For atoms that is about eleven orders of magnitude larger than light. The project will build upon Strathclyde's unique experience in generating a toroidal, smooth trapping potential, where atomic waves can propagate in opposite directions (4,5).