Using Atom Interferometry to Search for New Forces
8/17/2009
5 citations. An interdisciplinary paper connecting precision atomic physics to particle physics beyond the Standard Model.
The Problem
Many extensions of the Standard Model predict new forces that operate at short distances, from micrometers to kilometers. These include forces mediated by light scalar particles (moduli from string compactifications, dilatons), new gauge bosons with very weak couplings, and modifications to gravity at short range predicted by extra-dimensional scenarios. The existing experimental constraints on such forces came primarily from torsion balance experiments and Casimir force measurements, which had set limits at distances down to roughly 10 micrometers. But there was a gap: at distances between 100 micrometers and 1 kilometer, the constraints were surprisingly weak, and theoretically motivated new forces could be hiding in that window.
The Key Idea
Atom interferometry, a rapidly advancing technology that uses the wave nature of atoms to make extraordinarily precise measurements of accelerations, was already achieving sensitivities competitive with the best gravitational experiments. The paper proposes a specific experimental configuration, based on existing technology, that could improve sensitivity to new short-distance forces by up to a factor of 100 at ranges from 100 micrometers to 1 kilometer. Near-future advances in atom interferometry would push the limits further. The key advantage of atom interferometry over mechanical experiments is that atoms are identical, well-characterized quantum systems: systematic errors from material properties, surface effects, and electrostatic patches that plague macroscopic force measurements are absent. The paper maps the theoretically motivated parameter space (coupling strength versus range) and shows that atom interferometers could probe regions that no other technique could access.
Impact
Rosi et al. (Physical Review A, 2015, 108 citations) built a cold-atom gravity gradiometer and used it to set constraints on Yukawa-type fifth forces at the 10 cm scale, a direct experimental realization of the program this paper proposed. Geraci et al. (Physical Review D, 2015, 54 citations) extended the approach to nanosphere interferometry, projecting 10,000-fold improvements over prior limits by bringing matter-wave interference closer to source masses. The broader program of using quantum sensors to search for fundamental physics has grown into a major community effort: a 2023 whitepaper on “Quantum Sensors for High Energy Physics” (32 citations) frames the entire field, covering dark matter, dark sectors, and gravitational wave detection with atom interferometric techniques. Tino’s 2021 review in Quantum Science and Technology, “Testing gravity with cold atom interferometry,” surveys the full scope of what the field has become: gravitational constant measurements, equivalence principle tests, modified gravity searches, dark matter and dark energy probes, and gravitational wave detection. Experiments like MAGIS at Stanford and AION at Oxford are now targeting exactly the parameter space this paper mapped.
Recollections
This paper had a difficult birth. It started as a collaboration with Peter Graham, Savas Dimopoulos, and Mark Kasevich, but for whatever reason they dropped off. The paper was mostly finished over a year before publication but just sat stagnating. It was also a period when I had a lull in publications, and I felt the pressure of having two years of work with nothing to show for it.
Over the summer, while Mira and I were traveling, she motivated me to finish the paper. I remember working at cafes in Dubrovnik, editing draft after draft and refining calculations. One of the things that didn’t make it into the final version were several alternate interferometry designs that were more speculative in terms of experimental feasibility. I don’t think those designs have ever been published. The paper that came out was the conservative core of what had been a more ambitious project. The unpublished designs included a “butterfly” geometry using reflected Raman beams off a Casimir shield to create three momentum states for short-distance force measurement, and a “rose” configuration sensitive to the third derivative of the gravitational potential (V'''). A literature search shows that the geometric concepts were independently reinvented: Oh et al. (2020) adopted the “butterfly” name for gradient-sensitive Stern-Gerlach interferometry, and Rosi et al. (PRL, 2015) made the first measurement of gravity-field curvature using three simultaneous interferometers. But neither used the specific mechanism of reflected Raman beams off a shield to generate the multi-path topology. That particular approach, as far as I can tell, remains original to these unpublished notes.