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Metastability Transfer Spectroscopy with Two like Ions in the Same Trap

Hans Dehmelt and Warren Nagourney
Proceedings of the National Academy of Sciences of the United States of America
Vol. 85, No. 20 (Oct. 15, 1988), pp. 7426-7427
Stable URL: http://www.jstor.org/stable/32955
Page Count: 2
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Abstract

High-resolution optical spectroscopy of an individual trapped ion is hampered by lack of sharp lasers. This suggests the use of a second metastable excited ion as an ultrasharp light source. To this end, laser-cool two barium ions to an equilibrium distance of ≈ 8 μ m on the z (symmetry) axis of the trap and, in this (earth)(Ba+)2-molecule, visually or photoelectrically identify them as A and B by their location. Briefly turn on a 455-nm spectral lamp until one of the ions, say the A ion, is pumped into the metastable D5/2 level and turns invisible. Focus on the visible, spatially well-resolved B ion and turn off the blue and red illumination lasers for ≈ 15 s. Then turn them back on again and check on whether the excitation by chance has been transferred to the B ion and is now in the D5/2 level and dark while the A ion is bright. The cross section for absorption of the λ (D5/2→ S1/2) $\equiv \lambda _{0}$ = 1.76 μ m radiation by a stationary ion can be >λ 02/2π . Thus, by pushing the two ions together to ≈ λ 0/4 by turning on a much stronger trapping field during the excitation exchange period, one might be able to detect excitation transfer in >10% of the attempts. The ions are tuned relative to each other by a 0- to 10-mV/cm variable dc field in the z direction, which displaces them axially and causes them to see different rf fields, which Stark-shifts their frequencies. In this way, a resonant transfer response as sharp as twice the natural width of the D5/2 level, 11 mHz or a Q ≈ 0.4 × 1017, might be demonstrated.

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