Atom Wave Interferometry for Scientific Measurement

Abstract:

Atom wave interferometry is useful for navigation and scientific measurements because atoms have mass and are subject to gravity and acceleration. Atom wave accelerometers, gyros, sensitive gravity gradiometers, and gravitational wave detection are all feasible. We can now build the atomic equivalents of optical interferometers by using laser pulses to make partial excitation of atoms into higher energy levels. But these also transfer momentum and the excited atoms have different trajectories, requiring complex equipment and additional laser pulses before they can be brought back to interfere coherently with their other halves. Only a few kinds of atoms have suitable structures with long-lived excited states. To make atom wave interferometry most useful, it is necessary to produce and cool clouds of atoms to extremely low kinetic temperatures, nanoKelvins or less, otherwise the clouds disperse before they can interfere coherently with themselves. Work is ongoing at Stanford University and at AOSense, Inc. in partnership with NASA, to miniaturize the equipment and make it capable of qualification for space missions. Results from the Stanford 10-m tower already show that an atom cloud can be excited and separated coherently into two clouds up to 50 cm apart, and then recombined. Based on these results we know that atom wave gravity gradiometers with today’s technology could already improve dramatically on measurements of the changes of the Earth’s gravitational shape obtained by the GRACE mission. We also see a path for further improvement, sufficient to enable detection of extremely weak gravitational waves using space missions, complementing the results of LIGO and the planned LISA detector. Recent progress, propelled by the importance of the possible measurements, and Federal support, shows that the dreams of only a few years ago can become reality.