Atom Interferometry tests of the isotropy of post-Newtonian gravity (0710.3768v2)

Abstract: We present a test of the local Lorentz invariance of post-Newtonian gravity by monitoring Earth's gravity with a Mach-Zehnder atom interferometer that features a resolution of about 8*10^-9g/Hz^1/2, the highest reported thus far. Expressed within the standard model extension (SME) or Nordtvedt's anisotropic universe model, the analysis limits four coefficients describing anisotropic gravity at the ppb level and three others, for the first time, at the 10ppm level. Using the SME we explicitly demonstrate how the experiment actually compares the isotropy of gravity and electromagnetism.

• The paper presents a rigorous atom interferometry experiment that tests local Lorentz invariance by measuring phase shifts in Earth’s gravitational field.
• It employs a Mach-Zehnder interferometer to achieve a resolution near 8×10⁻⁹ g/√Hz, setting constraints on gravity anisotropy coefficients at ppb levels.
• The findings tighten limits on potential violations of general relativity and position atom interferometry as a superior tool over classical gravimeters.

Analyzing Local Lorentz Invariance in Post-Newtonian Gravity through Atom Interferometry

This paper presents a meticulous examination of the isotropy of post-Newtonian gravity, utilizing the capabilities of atom interferometry. Conducted by researchers at multiple prestigious institutions, the experiment explores the local Lorentz invariance (LLI) aspect of Einstein's Equivalence Principle (EEP) by testing Earth's gravitational field. The researchers achieved this using a Mach-Zehnder atom interferometer, which boasts an unprecedented resolution of approximately $8 \times 10^{-9}$ g/$\sqrt{\text{Hz}}$.

The experiment capitalizes on the high sensitivity of atom interferometry, achieving a significant milestone in gravitational measurements. By inducing a controlled superposition of atomic states, the interferometer effectively measures the phase shifts attributable to gravity, enabling the detection of potential anisotropies in the gravitational field. The paper employs the standard model extension (SME) and Nordtvedt's anisotropic universe model to frame and interpret the measurements. Within these theoretical constructs, the analysis yields stringent constraints on the coefficients that describe anisotropic gravity—four coefficients are limited at the parts-per-billion (ppb) level and three others at the parts-per-million (ppm) level for the first time.

Significantly, the research demonstrates the sensitivity of their interferometric gravimeter, which surpasses traditional classical instruments such as the FG-5 optical interferometer gravimeter by a factor of approximately 20. This parallels advancements in atomic clocks and opens the door for improved tests of gravitational theories and potential new physics beyond the current paradigm of general relativity and the standard model of particle physics.

The results presented provide critical insights into the fundamental symmetries of nature, specifically the isotropy of spacetime as predicted by the theories of relativity. The constraints on LLI suggested by this experiment are vital data points in the ongoing quest to reconcile general relativity with quantum mechanics. This work represents an intersection of theoretical physics and experimental precision, illustrating how atomic physics and quantum optics can provide probes of fundamental forces.

The implications of this paper reach into both theoretical and practical domains. Theoretically, it challenges gravitational theories by further narrowing the parameter space for Lorentz invariance violations. Practically, it highlights the potential of atom interferometers in geophysical research, precise gravitational measurement, and testing relativistic predictions under terrestrial conditions. In advancing the precision of these experiments, it spurs technological and methodological innovations that could sharpen the tools of fundamental physics investigations.

Looking forward, enhancements to atom interferometry, such as minimizing tidal influences or employing horizontal interferometer configurations, hold promise for refining these measurements. Such advancements may drive future experimental approaches that test the nature of gravity and spacetime with even greater accuracy, potentially paving the way for novel insights into quantum gravity and the unification of forces. This paper exemplifies progress towards these ambitious goals, underscoring the dynamic interplay between experimental capability and theoretical exploration in contemporary physics research.