We discuss the possibility of trapping polar molecules in the standing-wave
electromagnetic field of a microwave resonant cavity. Such a trap has several
novel features that make it very attractive for the development of ultracold
molecule sources. Using commonly available technologies, microwave traps can be
built with large depth (up to several Kelvin) and acceptance volume (up to
several cm^3), suitable for efficient loading with currently available sources
of cold polar molecules. Unlike most previous traps for molecules, this
technology can be used to confine the strong-field seeking absolute ground
state of the molecule, in a free-space maximum of the microwave electric field.
Such ground state molecules should be immune to inelastic collisional losses.
We calculate elastic collision cross-sections for the trapped molecules, due to
the electrical polarization of the molecules at the trap center, and find that
they are extraordinarily large. Thus, molecules in a microwave trap should be
very amenable to sympathetic and/or evaporative cooling. The combination of
these properties seems to open a clear path to producing large samples of polar
molecules at temperatures much lower than has been possible previously.Comment: 10 pages, 3 figure