Ramsey Gravity Resonance Spectroscopy with Ultracold Neutrons
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amsey Gravity Resonance Spectroscopy with Ultracold Neutrons R. Sedmika, *, J. Bosinaa, b, P. Geltenbortb, A. Ivanova, T. Jenkeb, J. Mickoa, b, M. Pitschmanna, T. Rechbergera, S. Rocciab, M. Thalhammera, and H. Abelea aTechnische
Universität Wien, Atominstitut, Vienna, 1020 Austria Laue-Langevin, Grenoble, 38042 France *e-mail: [email protected]
bInstitut
Received July 5, 2019; revised August 30, 2019; accepted September 10, 2019
Abstract—Neutrons appear to be ideal test particles to search for non-Newtonian gravity at micrometer separations, as with their vanishing electrostatic sensitivity they avoid many of the problems appearing with other test masses. Over the past decade, the qBounce collaboration has developed a technique named gravity resonance spectroscopy (GRS) that allows probing the bound states of ultracold neutrons in the Earth’s gravitational field. With the successful implementation of Ramsey spectroscopy and long interaction times, the setup presented promises to test Einstein’s gravity with unprecedented sensitivity. Keywords: ultracold neutrons, gravity, spectroscopy, dark energy, dark matter DOI: 10.1134/S1027451020070423
INTRODUCTION Understanding the nature of dark energy and dark matter is considered one of the most pressing problems of physics. In the present cosmological standard model Λ-CDM, these effects are pragmatically described via the cosmological constant and a noninteracting gravitating fluid, respectively – both being empiric models only. In addition, significant tensions exist between different observations of the Hubble constant [1] and of the cosmological density fluctuation parameter [2], as well as the lensing potential [3] that cannot be explained within Λ-CDM. On the theoretical side, sterile neutrinos, axions (and more generally, weakly interacting massive particles) for dark matter and quintessence with screening for dark energy are presently seen as some of the most promising candidates for constituting the dark sector [4]. A common effect of most of these hypothetical new interactions is that they would cause small deviations from Newtonian gravity on small scales – a fact that motivates metrological force measurements. Common approaches are torsion balances [5], atom interferometry [6], and Casimir experiments [7]. Most of these are plagued by electrostatic disturbances that limit the achievable precision. An alternative way to avoid electrostatic problems is to use ultracold neutrons as test particles. The latter approach has been followed by the qBounce collaboration [8, 9] and is the subject of this article.
GRAVITY RESONANCE SPECTROSCOPY Ultracold neutrons are reflected specularly from almost all surfaces under arbitrary angles. When placed on a horizontal plane, the potential well created by the Fermi pseudopotential of the surface material and the gravitational potential leads to discrete nonequidistant energy levels En of a few peV. As the differences between these states correspond to acoustic frequencies ν = ω/2π, transitions can unambiguously be ad
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