Microwave shielding of ultracold polar molecules

We use microwaves to engineer repulsive long-range interactions between ultracold polar molecules. The resulting shielding suppresses various loss mechanisms and provides large elastic cross sections. Hyperfine interactions limit the shielding under realistic conditions, but a magnetic field allows suppression of the losses to below $10^{-14}$~cm$^3$~s$^{-1}$. The mechanism and optimum conditions for shielding differ substantially from those proposed by Gorshkov \emph{et al.}\ [Phys.\ Rev.\ Lett.\ {\bf 101}, 073201 (2008)], and do not require cancelation of the long-range dipole-dipole interaction that is vital to many applications. \newline \newline [1] T.~Karman and J.M.~Hutson, Phys. Rev. Lett. {\bf 121}, 163401 (2018)