  We propose a new method of individual single-qubit addressing of linear
trapped-ion chains utilizing two ultrastable femtosecond frequency combs. For
that, we suggest implementing the single-qubit gates with two
counter-propagating frequency combs overlapping on the target ion and causing
the AC Stark shift between the qubit levels. With analytical calculations and
numerical modeling, we show that the arbitrary single-qubit rotations can be
indeed realized using only laser fields propagating along the ion chain. We
analyze the error sources for the proposed addressing method and prove that it
allows implementing the single-qubit gates with high fidelity.
