Results from a High-Sensitivity Search for Cosmic Axions

We report the first results of a high-sensitivity $\left(\sim {10}^{-23\mathrm{}}\mathrm{W}\right)$ search for light halo axions through their conversion to microwave photons. At the 90% confidence level, we exclude a Kim-Shifman-Vainshtein-Zakharov axion of mass $2.9\times {10}^{-6\mathrm{}}$ to $3.3\times {10}^{-6\mathrm{}}\mathrm{eV}$ as the dark matter in the halo of our galaxy.