Testing gravity with cold atom interferometry: results and prospects

Abstract

Atom interferometers have been developed in the last three decades as new powerful tools to investigate gravity. They were used for measuring the gravity acceleration, the gravity gradient, and the gravity-field curvature, for the determination of the gravitational constant, for the investigation of gravity at microscopic distances, to test the equivalence principle of general relativity and the theories of modified gravity, to probe the interplay between gravitational and quantum physics and to test quantum gravity models, to search for dark matter and dark energy, and they were proposed as new detectors for the observation of gravitational waves. Here I describe past and ongoing experiments with an outlook on what I think are the main prospects in this field and the potential to search for new physics.

Stern-Gerlach Interferometry for Tests of Quantum Gravity and General Applications

“…Over the years, there have been attempts to test the weak form of the equivalence principle in regimes wherein quantum effects become important. One of these experimental realizations employs the use of a Bragg-atom interferometer in a gravitygradiometer configuration to test the equivalence principle at the quantum scale; in this case, for 87 Rb atoms in a coherent superposition of internal (hyperfine) energy states [23]. Providing a detailed description of said experiment is not within the scope of this Perspective; nevertheless the key takeaway is that tests of the quantum aspects of the equivalence principle are in principle realizable and the use of quantum superpositions essentially allows one to probe the quantum aspects of fundamental laws and/or principles (which for many years have been thought to be purely classical, with possibly no quantum analogue) over suitably long time scales.…”

“…More recently, there have been attempts to measure G using cold atoms and quantum interferometric techniques (see for instance [55,56]), and these experiments have greatly aided in revealing the systematic errors that prevent one from discerning the value of G precisely. A more recent work by Asenbaum et al demonstrates a very interesting realization of a long-time drift large momentum transfer atom interferometer with ultracold 87 Rb atoms which can essentially be used as a gradiometer [57]. This gradiometric configuration can reach resolutions of down to 10 -9 s −2 and the macroscopic separation realizable between the interfering atomic wavepackets allows the authors to probe the coupling between atomic recoil effects and the spacetime curvature induced by the presence of a Pb source mass [57].…”

Spacetime Quantum Reference Frames and superpositions of proper times

“…The two effects discussed here, namely the superposition of special-relativistic time dilations and the superposition of gravitational redshifts are, in principle observable. A promising experimental system to carry out tests on the generalisation of these concepts could be atom interferometry [61].…”

A Cold-Atom Interferometer with Microfabricated Gratings and a Single Seed Laser

“…Over the past 30 years 16,17 , these LPAIs have demonstrated excellent laboratory sensitivity 18 and serious efforts are underway to advance the platform for real-world applications 19 and multi-axis sensors [20][21][22][23] . Their applications range from fundamental physics 18,24,25 and geophysics 26 to civil engineering 27 and navigation, but bringing cold-atom sensors out of a well-controlled laboratory into a dynamic environment poses significant physics and engineering challenges that must be addressed.…”

“…The light pulse sequence of LPAIs, e.g., π 2 → T → π → T → π 2 , coherently splits, redirects, and recombines atomic wavepackets for matter wave interference, where T is the interrogation time. During this process, the phase shifts experienced by the atoms are sensitive to inertial forces, resulting in an atomic interference fringe that provides acceleration and angular velocity information.Over the past 30 years 16,17 , these LPAIs have demonstrated excellent laboratory sensitivity 18 and serious efforts are underway to advance the platform for real-world applications 19 and multi-axis sensors [20][21][22][23] . Their applications range from fundamental physics 18,24,25 and geophysics 26 to civil engineering 27 and navigation, but bringing cold-atom sensors out of a well-controlled laboratory into a dynamic environment poses significant physics and engineering challenges that must be addressed.…”