Quantitative Study of Laser Cooling in a Penning Trap
Penning traps are currently being studied at our laboratory [1,2] and elsewhere [3,4] for use in atomic frequency standards. A Penning trap confines ions by a combination of a static, uniform magnetic field and a static, nonuniform electric field. The fact that the fields are static makes it feasible to laser cool more than 104 ions to low temperatures . In contrast, the radio-frequency (Paul) ion trap uses oscillating electric fields, which, in combination with the nonlinear Coulomb coupling between ions, cause heating and make it difficult to laser cool large numbers of ions . For either trap, large numbers increase the signal-to-noise ratio; low temperatures reduce the second-order Doppler shift .