Sub-recoil transverse momentum width in a cold ytterbium atomic beam

We demonstrate the generation of a slow ytterbium atomic beam with a transverse momentum width of 0.44(6) times the photon recoil associated with Bragg diffraction, and a flux of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>6.7</a:mn><a:mrow><a:mo>(</a:mo><a:mn>9</a:mn><a:mo>)</a:mo></a:mrow><a:mo>×</a:mo><a:msup><a:mn>10</a:mn><a:mn>6</a:mn></a:msup></a:mrow></a:math> atoms/s. This is achieved by applying momentum filtering through a long-lived metastable state to atoms prepared in a slow beam via two-dimensional transverse laser cooling. The resulting narrow momentum distribution enables efficient quasi-Bragg diffraction, which we exploit to realize a Bragg interferometer. These results mark a significant step toward continuous, high-precision, and magnetically insensitive angular rate measurements using cold alkaline-earth(-like) atomic beams.