Ultrasensitive Measurements of Forces Using Laser-Cooled Atoms

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Precise knowledge of the basic forces that govern and shape our universe is of paramount importance not only for fundamental science, but also for technological breakthroughs. This proposal seeks operational funding for a broad research program utilizing cold atoms for the precision measurements of a variety of basic forces. The main scientific goals of the proposal are: precision measurement of the gravitational acceleration g, precision measurement of the strength of the electromagnetic force (the fine-structure constant) and the precision measurement of the magnetic properties of atoms (g-factor ratios). All these experiments have recently achieved levels of precision associated with leading techniques using distinctive atom interferometric and coherent transient techniques. Results suggest that improvements in accuracy that can be achieved by addressing systematic effects will lead to a series of internationally competitive precision measurements in the near future. Atom interferometers (AIs) rely on the wave nature of cold atoms and intricate control of matter waves by pulses of laser light that act as beam splitters and mirrors. In this manner, the roles of light and matter are interchanged in comparison with traditional optical interferometers that use material elements to split and recombine light. The sensitivity of AIs are enhanced by increasing the enclosed area of space-time paths of atomic waves and by observing interference effects on extended time scales that are limited only by the transit time of atoms through laser beams. At York University a unique, echo type AI has been refined using a low cost apparatus to achieve measurement time scales of 250 ms, which is comparable to the time scales of widely known Raman AIs developed by leading international groups at Stanford, Berkeley, JPL, MPI, ENS and Bordeaux. Since the echo AI relies on one color laser excitation and does not require velocity selection, it offers reduced experimental complexity for precise measurements of gravitational acceleration g. An important element of this proposal will focus on improving the current level of precision of 75 parts per billion (ppb) achieved using a 50 ms measurement time scale and reaching an internationally competitive level of accuracy (0.5 ppb) using a 300 ms time scale. The significance of gravity measurements is related to their potential for calibrating industrial gravimeters that play an ubiquitous role in the exploration of natural resources such as minerals, petroleum, and natural gas, in the correction of tidal charts, and seismic monitoring. This initiative is supported by an industrial partner who is the leading manufacturer of commercial gravimeters. A different configuration of the same AI recently utilized a time scale of 100 ms and demonstrated a 37 ppb measurement of the momentum transferred to atoms by light, a quantity that can be related to the atomic fine structure constant "alpha". This universal coupling parameter defines the strength of light-matter interactions. We propose to reduce systematic effects and realize an accuracy of 0.5 ppb. This measurement is of interest to basic physics in the context of an international effort to define this fundamental constant using independent measurement techniques. The applicant's group has recently made the most precise measurement of a particular class of magnetic interactions that can be used as a sensitive test of atomic structure and for comparing the magnetic properties of matter with antimatter. Using a refined experiment, we propose to further improve the precision, avoid systematic effects and realize an accuracy of 100 ppb. Technological goals will focus on commercial applications of auto-locked laser systems developed by the applicant's group.