New limits on variation of the fine-structure constant using atomic dysprosium

TL;DR

This study uses atomic dysprosium spectroscopy to set new limits on the possible variation of the fine-structure constant over time and its coupling to gravity, achieving the most stringent constraints to date.

Contribution

It introduces a novel method using nearly-degenerate dysprosium states for sensitive tests of fundamental constant variations and provides the tightest experimental bounds so far.

Findings

No detectable variation of alpha over two years.

Established the best constraint on alpha's coupling to gravity.

Demonstrated the effectiveness of isotopic comparisons in systematic error suppression.

Abstract

We report on the spectroscopy of radio-frequency transitions between nearly-degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant, $\alpha$, owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of $\alpha$ competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in $^{164}$Dy and 235-MHz transition in $^{162}$Dy were measured over the span of two years. Linear variation of $\alpha$ is found to be $\dot{\alpha}/\alpha = (-5.8\pm6.9)\times10^{-17}$ yr$^{-1}$, consistent with zero. The same data are used to constrain the dimensionless parameter $k_\alpha$, characterizing a possible coupling of $\alpha$ to a changing gravitational potential. We find that $k_\alpha = (-5.5\pm5.2)\times10^{-7}$, essentially consistent with zero and the best constraint to date.