Laser-controlled entanglement between atomic qubits (‘spins’) and collective motion in trapped ion Coulomb crystals requires conditional momentum transfer from the laser. Since the spin-dependent force is derived from a spatial gradient in the spin–light interaction, this force is typically longitudinal—parallel and proportional to the average laser k-vector (or two beams’ k-vector difference), which constrains both the direction and relative magnitude of the accessible spin–motion coupling. Here, we show how momentum can also be transferred perpendicular to a single laser beam due to the gradient in its transverse profile. By controlling the transverse gradient at the position of the ion through beam shaping, the relative strength of the sidebands and carrier can be tuned to optimize the desired interaction and suppress undesired, off-resonant effects that can degrade gate fidelity. We also discuss how this effect may already be playing an unappreciated role in recent experiments.

捕获的离子库仑晶体中原子量子位（“自旋”）与集体运动之间的激光控制纠缠需要从激光进行有条件的动量转移。由于自旋相关力是从自旋光相互作用中的空间梯度得出的，因此该力通常是纵向的，与平均激光k矢量（或两个光束的k-矢量差），它限制了可到达的自旋运动耦合的方向和相对大小。在这里，我们展示了由于其横向轮廓的梯度，动量如何也可以垂直于单个激光束传输。通过束成形控制离子位置的横向梯度，可以调整边带和载流子的相对强度，以优化所需的相互作用，并抑制会降低栅极保真度的不良共振现象。我们还讨论了这种效应在最近的实验中可能已经起着不为人知的作用。