Molecular Lattice Clock for Precision Measurements and Ultracold Chemistry

The connection between the science of atoms and molecules and the big questions relating to the fundamental laws of nature is growing. Atoms and molecules obey the rules of quantum physics and thus have discrete energy states. The new techniques of controlling these quantum states are leading to a new generation of table-top experiments that can offer a glimpse of new physics over an extensive range of possible energies and types of fundamental interactions. The unprecedented reach of these experiments arises from an immaculate control of atomic and molecular quantum states as well as of any undesirable environmental influences. The fundamental insights gained from experiments in atomic and molecular physics include the tight constraints on processes that do not appear the same if viewed backwards in time; measurements of several fundamental constants of nature and tests of whether they are truly constant; searches for dark energy and dark matter that are not yet understood but are hypothesized to contain most of the energy of the universe; tests of Einstein's general relativity; and searches for possible new physical forces. Among many types of such experimental approaches, atomic clocks play a special role as extremely precise measurement tools, contributing to diverse scientific questions. On the other hand, molecules possess significantly more types of internal motions and quantum states than atoms, - for example, vibrations of the molecular constituents relative to each other. A clock based on molecular vibrations as its central mechanism can access new fundamental measurements that are out of reach for atomic clocks. Significant progress has recently taken place in molecular cooling and quantum state control. This makes possible state-of-the-art molecular clocks that utilize molecules cooled toward absolute zero, where motional degradation of precision and accuracy is nearly eliminated. In this project, a vibrational molecular lattice clock and its first scientific applications, including tests of Newtonian gravity at nanometer length scales, will be developed. Furthermore, this work makes broad connections between the fields of metrology, chemistry at ultracold temperatures, and fundamental physics.

Tightly trapping neutral molecules in an optical lattice affords measurements with a large signal-to-noise ratio while eliminating motional effects that lead to rapid decoherence of the molecular state superpositions. Recent work by the recipients of this grant resulted in the development of a molecular clock based on vibrational dynamics, with a quality factor Q of nearly a trillion, matching the best atomic clocks of just over a decade ago. Realizing molecular state-insensitive, trapping is a key to this success. This starting point makes the clock already applicable to a new class of high-precision measurements. The primary scientific application is for an ultraprecise measurement of an interatomic force. Combined with state-of-the-art quantum chemistry theory developed concurrently, this clock-based measurement should lead to the best limit on non-Newtonian gravity at the nanometer scale, while providing tests of molecular quantum electrodynamics. The molecular clock will also yield a model-independent measurement of the temporal stability of the electron-to-proton mass ratio. Further improvement in Q is contingent on understanding two-photon molecular photodissociation processes, which intellectually connects the molecular clock with the field of ultracold chemistry. The long coherence times between molecular states that will be achieved in this project are highly relevant to quantum-information and many-body experiments with molecular qubits.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.