  The dominant error sources for state-of-the-art laser-free trapped-ion
entangling gates are decoherence of the qubit state and the ion motion. The
effect of these decoherence mechanisms can be suppressed with additional
control fields, or with techniques that have the disadvantage of reducing gate
speed. Here, we propose using a near-motional-frequency magnetic field gradient
to implement a laser-free gate that is simultaneously resilient to both types
of decoherence, does not require additional control fields, and has a
relatively small cost in gate speed.
