Observation of resonant dipolar collisions in ultracold <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>Na</mml:mi><mml:mprescripts /><mml:none /><mml:mn>23</mml:mn></mml:mmultiscripts><mml:mmultiscripts><mml:mi>Rb</mml:mi><mml:mprescripts /><mml:none /><mml:mn>87</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> rotational mixtures

We report the investigation on dipolar collisions in rotational state mixtures of ultracold bosonic ^{23}a^{87}b molecules. The large resonant dipole-dipole interaction between molecules in rotational states of opposite parities brings about significant modifications to their collisions, even when an electric field is not present. In this work, this effect is revealed by measuring the dramatically enhanced two-body loss rate constants in...