We propose new experiments with high sensitivity to a possible spatial or temporal variation of the electron-to-proton mass ratio $μ\equiv m_e/m_p$. 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 $μ$, 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 $μ$.
Ultrastable frequency reference at 1.56 μm using a CO molecular overtone transition with the noise immune cavity-enhanced optical heterodyne molecular spectroscopy method
报道了一种基于一氧化碳12 C 16 O在1563 nm处的3ν振转结合带的超稳分子钟。激光稳定方案是基于频率调制（FM）饱和光谱在高精细度超低膨胀（ULE）玻璃光学腔中使用CO作为长期稳定腔谐振的分子参考。采用NICEOHMS FM调制方法，以保持高的信噪比，并避免由高精细度腔将激光频率噪声转换为幅度噪声。我们报告1秒时的艾伦偏差为1.8x10-12，在1000秒的平均后提高到3.5x10-14。
$\mathcal{P}$, $\mathcal{T}$-odd Faraday rotation in intracavity absorption spectroscopy with molecular beam as a possible way to improve the sensitivity of the search for the time reflection noninvariant effects in nature
Enhanced Sensitivity to the Time Variation of the Fine-Structure Constant and $m_p/m_e$ in Diatomic Molecules: A Closer Examination of Silicon Monobromide
