Stability of the proton-to-electron mass ratio

Understand

We report a limit on the fractional temporal variation of the proton-to-electron mass ratio as, obtained by comparing the frequency of a rovibrational transition in SF6 with the fundamental hyperfine transition in Cs.

• The SF6 transition was accessed using a CO2 laser to interrogate spatial 2-photon Ramsey fringes.
• The atomic transition was accessed using a primary standard controlled with a Cs fountain.
• This result is direct and model-free.