Geraci Research Group


Measuring gravity at the micron scale with laser cooled optically levitated microspheres

Why is gravity so much weaker than the other Standard Model forces? As a number of recent theories have suggested, by measuring how gravity behaves at sub-millimeter distances, important clues related to this 'hierarchy problem' can be obtained. Such measurements could lead to exciting new discoveries of physics beyond the Standard Model. However, the gravitational force between massive objects becomes weak very rapidly as their size and separation distance decreases, thus making ultra-precise measurements a necessity at sub-millimeter length scales.

We have developed an apparatus to trap and cool dielectric nanospheres using lasers. A levitated sphere in vacuum experiences minimal friction as it oscillates in a 'container' made of light. This low friction is the key to excellent force sensitivity. We have predicted that this new technique can advance our understanding of gravity at the micron length scale by a factor of ~100,000 or more. Thus far we have shown that optically trapped nanospheres in an optical standing wave trap can exceed the force sensitivity of any room temperature solid state force sensor by more than order of magnitude, and we have demonstrated calibrated force sensing at the zeptonewton (10-21 N) level, showing excellent promise for the short distance gravity tests.

Selected References

“Zeptonewton force sensing with nanospheres in an optical lattice”, Gambhir Ranjit, Mark Cunningham, Kirsten Casey, Andrew A. Geraci, Phys. Rev. A 93, 053801 (2016).

“Attonewton force detection using microspheres in a dual-beam optical trap in high vacuum”, Gambhir Ranjit, David P. Atherton, Jordan H. Stutz, Mark Cunningham, Andrew A. Geraci, Phys. Rev. A 91, 051805(R) (2015).

"Detecting high-frequency gravity waves using optically levitated sensors", Asimina Arvanitaki, and Andrew A. Geraci, Phys. Rev. Lett.110, 071105 (2013).

"Short-range Force Detection Using Optically Cooled Levitated Microspheres" Andrew A. Geraci, Scott B. Papp, and John Kitching, Phys. Rev. Lett. 102, 101101 (2010).

“Improved constraints on non-Newtonian forces at 10 microns” , Andrew A. Geraci, Sylvia J. Smullin, David M. Weld, John Chiaverini, and Aharon Kapitulnik, Phys. Rev. D 78, 022002 (2008).

The Axion Resonant Interaction Detection Experiment (ARIADNE)

Axions are particles predicted to exist in order to explain the apparent smallness of the neutron electric dipole moment. While also being promising candidates for dark matter, in tabletop experiments axions can mediate short-range spin-dependent forces between objects. In collaboration with Indiana University, Stanford University, Perimeter Institute, and the Institute for Basic Science in South Korea, we are developing the Axion Resonant InterAction Detection Experiment (ARIADNE) which will use nuclear magnetic resonance in laser-polarized Helium-3 gas to search for axion-induced interactions between the helium sample and an unpolarized tungsten mass. The method can potentially improve previous experimental bounds by several orders of magnitude and can probe deep into the theoretically interesting regime for the QCD axion, over a range that is complementary to existing axion search experiments.

Selected References

“Resonantly Detecting Axion-Mediated Forces with Nuclear Magnetic Resonance”, A. Arvanitaki and A. Geraci, Phys. Rev. Lett. 113, 161801 (2014).

“Progress on the ARIADNE Axion Experiment”, A. A. Geraci for the ARIADNE Collaboration et al. In: Carosi G., Rybka G., van Bibber K. (eds) Microwave Cavities and Detectors for Axion Research. Springer Proceedings in Physics, vol 211. Springer, Cham (2018).

Cold atoms coupled to micro-mechanical oscillators

We study the interactions between laser-cooled atoms and magnetic micro- and nano-mechanical resonators. Micro-cantilevers have demonstrated sub-attonewton force sensitivity, enabling single electron-spin detection in solids. They can also be used to manipulate and probe the spin states of trapped cold atoms with single-spin sensitivity and sub-micron spatial resolution. Ultimately, hybrid systems consisting of cold atoms coupled with micro- and nano-mechanical devices may lead to new applications in quantum information science or quantum simulation.

We have conducted an experiment to excite magnetic resonance in an ensemble of laser-cooled trapped Rb atoms using a capacitively driven cantilever functionalized with a magnetic tip. For those atoms in a "resonant slice" with their Larmor frequency coinciding with the mechanical frequency of the beam, the mechanical oscillator drives coherent atomic spin precession. This results in Zeeman state transitions in the atomic sample. Additionally, we plan to detect the backaction of atomic spins on the motion of a cantilever.

In our current project, we are studying the coupling between an optically trapped silica nanosphere and laser-cooled atoms. The cold atoms will be used to sympathetically cool the nanosphere; it is predicted that this method can be used to cool the nanosphere to its quantum ground state. Additionally, the system is designed so that the cooling and trapping can be turned off, which allows observation of the strong-coupling dynamics and matter-wave phenomena.

Selected References

“Resonant interaction of trapped cold atoms with a magnetic cantilever tip”, Cris Montoya, Jose Valencia, Andrew A. Geraci, Matthew Eardley, John Moreland, Leo Hollberg, and John Kitching, Phys. Rev. A 91, 063835 (2015).

“Cold atoms as a coolant for levitated optomechanical systems”, Gambhir Ranjit, Cris Montoya, and Andrew A. Geraci Phys. Rev. A 91, 013416 (2015).

“Sensing Short-Range Forces with a Nanosphere Matter-Wave Interferometer”, Hart Goldman, Andrew A. Geraci, Phys. Rev. D 92, 062002 (2015).

"Ultracold mechanical resonators coupled to atoms in an optical lattice" Andrew A. Geraci and John Kitching, Phys. Rev. A 80, 032317 (2009).

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