171Yb+ Single-Ion Optical Frequency Standards

We present work on a frequency standard based on the ²S_1/2(F=0, m_F=0)rarr²D_3/2(F=2, m_F=0) electric quadrupole transition in ¹⁷¹Yb⁺ at 688 THz, and future plans for a frequency standard based on the ²S_1/2(F=0, m_F=0)rarr²F_7/2(F=3, m_F=0) electric octupole transition in the same ion at 642 THz. Direct measurement of the ratio of these two frequencies, derived from a single ytterbium ion, constitutes a sensitive test for the temporal constancy of the fine structure constant.