  We have detected the four 18cm OH lines from the $z \sim 0.765$ 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 $z \sim 0.765$
absorber and the $z \sim 0.685$ lens toward B0218+357 to place stringent
constraints on changes in $F \equiv g_p [\alpha^2/\mu]^{1.57}$. We obtain
$[\Delta F/F] = (0.44 \pm 0.36^{\rm stat} \pm 1.0^{\rm syst}) \times 10^{-5}$,
consistent with no evolution over the redshift range $0 < z < 0.7$. The
measurements have a $2 \sigma$ sensitivity of $[\Delta \alpha/\alpha] < 6.7
\times 10^{-6}$ or $[\Delta \mu/\mu] < 1.4 \times 10^{-5}$ to fractional
changes in $\alpha$ and $\mu$ over a period of $\sim 6.5$ Gyr, half the age of
the Universe. These are among the most sensitive current constraints on changes
in $\mu$.
