Constraints on Changes in Fundamental Constants from a Cosmologically Distant OH Absorber or Emitter

We have detected the four 18 cm OH lines from the z∼0.765 gravitational lens toward PMN J0134–0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the z∼0.765 absorber and the z∼0.685 lens toward B0218+357 to place stringent constraints on changes in F≡g_p[α²/μ]^1.57. We obtain [ΔF/F]=(0.44±0.36^stat±1.0^syst)×10^-5, consistent with no evolution over the redshift range 0<z≲0.7. The measurements have a 2σ sensitivity of [Δα/α]<6.7×10^-6 or [Δμ/μ]<1.4×10^-5 to fractional changes in α and μ over a period of ∼6.5  G yr, half the age of the Universe. These are among the most sensitive constraints on changes in μ.