Measuring gravity at the micron-scale with laser-cooled trapped microspheres: a renewal proposal

Project: Research project

Project Details

Description

Project Summary
Overview. In this proposal, an experiment will continue to be developed using laser-cooled trapped
microspheres to test for Yukawa-type deviations from Newtonian gravity at the micron length scale. The
project is conceptually divided into three tasks: (1) investigation of systematic errors in preliminary gravity
measurements, (2) a dedicated gravitational force search at the � 1 �m-scale with the goal of acquiring 106s
of integrated data, and (3) in-parallel development of novel methods for trapping and cooling the levitated
nanoparticles, including sympathetic cooling with cold atoms.
Intellectual Merit. Gravity is the least understood fundamental force of nature: there is a 16 order of
magnitude disparity between the energy scale of quantum gravity and that of the other Standard Model
(electro-weak) forces. The mystery can be cast in another way: why is gravity so much weaker than the
other Standard Model forces? As a number of recent theories have suggested, important clues related to
this \hierarchy problem" can be obtained by measuring how gravity behaves at sub-millimeter distances.
However, the gravitational force between massive objects becomes weak very rapidly as their size and sep-
aration distance decreases, thus making ultra-sensitive measurements a necessity at sub-millimeter length
scales. Cryogenic micro-cantilever beams have been previously used by the Kapitulnik group at Stanford to
measure gravitational forces at sub-100 micron length scales at the atto-Newton (10􀀀18 N) level. While a
graduate student, the PI took part in such a measurement that extended the search for new physics, with
a factor of 10,000 improvement over earlier gravity measurements at the 20 micron length scale. These
results have placed signi�cant bounds on physics beyond the Standard Model. The force sensitivity of these
micro-cantilever experiments is limited by mechanical dissipation. By optically levitating the force sensor,
an exquisite decoupling from the environment is possible. Our group has achieved calibrated 10􀀀21 N force
sensitivity with optically trapped laser-cooled silica nanospheres { over an order of magnitude better than
any solid-state room-temperature force sensor. When combined with the ability to precisely position the
nanosphere test mass within micron distances of a surface, as our team has recently demonstrated, this new
technique could ultimately advance our understanding of gravity at the micron length scale by a factor of
103 to 105, and may lead to ground-breaking discoveries. In addition to studies of short-range gravitational
forces, the proposed experimental technique will also enable novel investigations of Casimir forces in un-
explored regimes. Novel trapping and cooling methods will be investigated for the trapped nanoparticles,
including sympathetic cooling with cold atoms.
Broader Impacts. One graduate student and one postdoctoral researcher will be broadly trained in
experimental physics and nanofabrication, and encouraged to present results at scienti�c meetings. By
participating in this highly interdisciplinary research project, students will be well equipped for scienti�c
careers. In addition, e�orts to include women and minority researchers in the project will be undertaken.
The group has a record of including underrepresented researchers. For example the primary graduate student
and postdoc who worked on this project during the previous funding cycle were both Hispanic physicists.
One postdoc and 4 of the 8 graduate students who have recently worked i
StatusActive
Effective start/end date7/15/216/30/22

Funding

  • National Science Foundation (PRESPEND)