Ground-state electromagnetically-induced-transparency cooling of 171Yb+ions in a polychromatic field

We propose a scheme of deep laser cooling of 171Yb+, which is based on the effect of electromagnetically induced transparency (EIT) in a polychromatic field with three frequency components resonant with optical transitions of the 2S1/2 -> 2P1/2 line. The deep cooling down to the ground motional state in a trap allows for a significant suppression of the second-order Doppler shift in the frequency standard. Moreover, in our scheme, there is no need to use a magnetic field, which is required for Doppler cooling of 171Yb+ in a field with a two frequency component. Cooling without the use of a magnetic field is important for the deep suppression of quadratic Zeeman shifts of clock transitions due to an uncontrolled residual magnetic field.