CAREER: Precision Measurements with Ultracold Diatomic Molecules

Columbia University, New York NY

Investigators

Abstract

Non-technical description: The answer to the question "what time is it?" ultimately traces back to master clocks that are based on the internal ticking of atoms. Increasing the accuracy of these master clocks has in the past enabled such innovations as the GPS systems that we use in our cars and smartphones to locate our position on the globe. Future improvements in clocks can be expected to enable similar innovations that are only just beginning to be imagined. The present project seeks to extend the scope of the science and technology we can achieve by keeping track of time ever more accurately, using molecules instead of atoms. Molecules present the possibility of a quantum clock based on different physics than atomic clocks: nuclear vibrations rather than electronic transitions. Simple molecules that consist of two atoms will be created near the temperature of absolute zero and trapped in standing waves of light to ensure nearly complete isolation from the environment. These strontium molecules possess very well defined internal energy states that allow precise manipulation and probing with laser light. This clock is sensitive to variations in the electron-to-proton mass ratio that may occur as the universe evolves, and to yet undiscovered forces that might appear at nanometer scales. Technical description: A new class of ultracold diatomic molecules based on laser-cooled strontium atoms was recently demonstrated by the primary investigator's research group. This work (based on optical trapping, manipulation, and imaging of these dimers) will enable precision measurements in molecular physics as well as tests of fundamental laws that may indicate new physics beyond the Standard Model. Initial work indicates that by applying atomic lattice-clock techniques to this molecule in both the excited and ground states, a direct measurement of the nonadiabatic Coriolis mixing angles of the molecular wavefunctions can be performed; these angles are critical for describing weak molecular bonding near the atomic continuum. This project will further characterize the transition from adiabatic to nonadiabatic behavior in these weakly bound systems. Additionally, tightly bound ultracold ground-state strontium dimers will be created for vibrational spectroscopy, or a molecular vibrational clock. If the mass scaling of the van der Waals type interatomic interaction is better understood, this clock can potentially improve the knowledge of nanometer-scale mass-dependent forces by several orders of magnitude. When the systematic effects of lattice spectroscopy of this molecule are better characterized and state-insensitive lattice trapping is optimized as part of this project, this molecular clock can set the best model-independent limit on the stability of the electron-to-proton mass ratio. Robust molecular clocks have applications in geodesy, navigation, and tests of fundamental science. Special efforts are made to involve young public school students from local New York City neighborhoods and expose them to the day-to-day work of scientists.