Spin-locked internally resonant ion cyclotron excitation for magnetic resonance trapped ions

Abstract

We have recently proposed internally resonant ion cyclotron excitation (IRICE) as a tool for detecting the magnetic resonance (MR) spectra of trapped ions. A magnetic field gradient modulated at both the Larmor and cyclotron frequencies leads to cyclotron acceleration proportional to the transverse magnetic moment of a coherent state of the particle and radiation field. In the presence of a magnetic bottle, the resulting shift in the axial trapping frequency due to this spin-dependent work can be made much larger than the shift due directly to a spin flip. Our original proposal, however, was effective only for fields sharply resonant with the Larmor frequency, limiting its applicability primarily to cw MR experiments. For Fourier transform experiments, excitation of ion motion over the entire MR spectral width is desirable. FT experiments would require a large IRICE Larmor bandwidth. We present a spin-locked version of IRICE (SL-IRICE), where an additional magnetic field at the Larmor frequency is used to lock the transverse magnetic moment in phase with the IRICE field gradient. Illustrative experimental designs indicate that spectral widths sufficient for FT NMR experiments are practical. In the proposed experiment, the time evolution from a period of high-resolution precession modulates the probability ofmore » a net axial frequency shift between two detection periods. Quantum and semiclassical analyses of the excitation process agree quantitatively. Simulated signals including estimated noise illustrate the feasibility of the method.« less