A cryofuge for cold-collision experiments with slow polar molecules

Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to prepare dense samples at low velocities. Here we present a solution to this goal by a non-conventional approach dubbed cryofuge. It employs centrifugal force to bring cryogenically cooled molecules to kinetic energies below $1$K$\times k_B$ in the laboratory frame, with corresponding fluxes exceeding ${10}^{10}$/s at velocities below $20$m/s. By attaining densities higher than ${10}^9$/cm${}^3$ and interaction times longer than $25$ms in samples of fluoromethane as well as deuterated ammonia, we observe cold dipolar collisions between molecules and determine their collision cross sections.