Constraints on a Spin-Dependent Exotic Interaction between Electrons with Single Electron Spin Quantum Sensors.

A new laboratory bound on the axial-vector mediated interaction between electron spins at micrometer scale is established with single nitrogen-vacancy (NV) centers in diamond. A single crystal of p-terphenyl doped pentacene-d(14) under laser pumping provides the source of polarized electron spins. Based on the measurement of polarization signal via nitrogen-vacancy centers, we set a constraint for the exotic electron-electron coupling g(A)(e)g(A)(e), within the force range from 10 to 900 mu m. The obtained upper bound of the coupling at 500 mu m is |g(A)(e)g(A)(e)/4 pi hc| <= 1.8 x 10(-19), which is one order of magnitude more stringent than a previous experiment. Our result shows that the NV center can be a promising platform for searching for new particles predicted by theories beyond the standard model.