Proposed Test of the Equivalence Principle with Rotating Cold Polar Molecules

We propose a novel scheme for testing the equivalence principle with rotating cold polar molecules whose angular momenta are polarized at different states. Molecules in specific rotational states are selected out via the hexapole state-selection technique and the gravitational acceleration g of molecules is measured by measuring the Doppler shift of the molecules free falling in the gravitational field. Some other possible methods of rotating molecules and measuring g are also mentioned. Molecules, as the test masses, have higher rotating speed and smaller dimension in comparison with mechanical gyroscopes and may open a new way for testing the equivalence principle and the possible coupling between rotation and gravity.