Enhanced sensitivity to variation of $m_{e}/m_{p}$ in molecular spectra

TL;DR

This paper proposes using nearly-degenerate vibrational levels in ultracold Cs₂ molecules to detect tiny variations in the electron-to-proton mass ratio, leveraging their high sensitivity and narrow spectral lines.

Contribution

It introduces a new experimental approach utilizing specific molecular vibrational level pairs in Cs₂ for enhanced detection of variations in fundamental constants.

Findings

Identifies nearly-degenerate vibrational levels in Cs₂ suitable for sensitive measurements.

Shows potential for high-precision detection of $5$ variations using ultracold molecules.

Highlights the advantage of narrow spectral lines in long-lived molecular states.

Abstract

We propose new experiments with high sensitivity to a possible spatial or temporal variation of the electron-to-proton mass ratio $\mu \equiv m_e/m_p$. We consider a nearly-degenerate pair of molecular vibrational levels, where each state is associated with a different electronic potential. The change in the splitting between such levels, with respect to a change in $\mu$, can be large both on an absolute scale and relative to the splitting. We demonstrate the existence of such pairs of levels in Cs$_2$. The narrow spectral lines achievable with ultracold Cs$_2$ in these long-lived levels make this system promising for future searches for small variations in $\mu$.