Cyclotron frequency shifts arising from polarization forces

The cyclotron frequency of a charged particle in a uniform magnetic field B is related to its mass m and charge q by the relationship omega(c) = qB/m. This simple relationship forms the basis for sensitive mass comparisons using ion cyclotron resonance mass spectroscopy, with applications ranging from the identification of biomolecules(1) and the study of chemical reaction rates(2) to determinations of the fine structure constant of atomic spectra(3). Here we report the observation of a deviation from the cyclotron frequency relationship for polarizable particles: in high-accuracy measurements of a single CO+ ion, a dipole induced in the orbiting ion shifts the measured cyclotron frequency. We use this cyclotron frequency shift to measure nondestructively the quantum state of the CO+ ion. The effect also provides a means to determine to a few per cent the body-frame dipole moment of CO+, thus establishing a method for measuring dipole moments of molecular ions for which few comparably accurate measurements exist(4-6). The general perturbation that we describe here affects the most precise mass comparisons attainable today(7,8), with applications including direct tests of Einstein's mass-energy relationship(9) and charge-parity-time reversal symmetry(10), and possibly the weighing of chemical bonds(7).