Quantum Gravity Gradiometer Sensor for Earth Science Applications

Quantum gravity gradiometers based on atom interferometry hold the promise for greater sensitivity and suitability for Earth science applications. Such instruments can potentially provide not only high resolution mapping of mass distribution both above and below the surface of the planet, but also temporal monitoring of its dynamical processes. These capabilities will significantly advance our knowledge of the solid Earth, the oceans, and under ground water. The underlying principle of atom-interferometry is the quantum particle-wave duality. According to quantum mechanics, atoms behave as waves, as does light. One can therefore construct an interferometer based on atom-waves much like laser interferometers. Because of the finite mass of the atom, matter-wave interferometers are intrinsically extremely sensitive to the gravity. Advances in laser cooling of neutral atoms and atom optics in recent years have made such atomwave interferometers more practical than ever. We are developing a quantum gravity gradiometer (QGG) sensor towards a portable and eventually flyable system. In our ground-based gradiometer implementation, two atom-interferometer-based accelerometers will be placed one above the other vertically. Each accelerometer is realized in an atomic fountain, where cold atoms are first produced in a magneto-optical trap by laser cooling. The atoms are then launched out of the trap and subsequently divided in two paths by laser light, and then recombined to form a Mach-Zehnder-type interferometer. Gravity, acting on the moving atoms, distorts the phase of the matter waves and therefore changes the interference pattern, which can be readily detected via laser resonance fluorescence. In this paper, we will describe some of the underlying principles of QGG, discuss its potential capability, and report on the progress of our hardware development to date. We will also discuss the development of a new data recovery algorithm as part of the QGG sensor, which is required in view of the new hardware capability. This work was carried out at Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.