Proposed Experimental Test Of Exotic Monopole-Dipole Interaction At The Micrometer Range

Here we propose an experiment to test the exotic spin-dependent interaction that can be mediated by axion-like particles. A sensitive cantilever is used to measure the force between a Bi4Ge3O12 (BGO) microsphere and a spin-polarized magnetic structure. The magnetic structure consists of alternate reversely spin-polarized electrons. The magnetic structure is to be driven to oscillate during data acquisition, thus the exotic force signal is modulated to the high harmonics of the drive frequency. This helps to suppress the spurious background signal. The separation between the BGO sphere and the magnetic structure can be as close as 3.5 mu m, and the force sensitivity is expected to be similar to 1 fN. If a Null result is obtained, the constraints on the coupling constant could be four orders of magnitude stronger than the current status of the experimental test at lambda = 10 mu m.