Single-site Rydberg addressing in 3D atomic arrays for quantum computing with neutral atoms

Neutral atom arrays are promising for large-scale quantum computing especially because it is possible to prepare large-scale qubit arrays. An unsolved issue is how to selectively excite one qubit deep in a 3D atomic array to Rydberg states. In this work, we show two methods for this purpose. The first method relies on a well-known result: in a dipole transition between two quantum states driven by two off-resonant fields of equal strength but opposite detunings $\pm\Delta$, the transition is characterized by two counter-rotating Rabi frequencies $\Omega e^{\pm i\Delta t}$~[or $\pm\Omega e^{\pm i\Delta t}$ if the two fields have a $\pi$-phase difference]. This pair of detuned fields lead to a time-dependent Rabi frequency $2\Omega \cos(\Delta t)$~[or $2i\Omega \sin(\Delta t)$], so that a full transition between the two levels is recovered. We show that when the two detuned fields are sent in different directions, one atom in a 3D optical lattice can be selectively addressed for Rydberg excitation, and when its state is restored, the state of any nontarget atoms irradiated in the light path is also restored. Moreover, we find that the Rydberg excitation by this method can significantly suppress the fundamental blockade error of a Rydberg gate, paving the way for a high-fidelity entangling gate with commonly used quasi-rectangular pulse that is easily obtained by pulse pickers. Along the way, we find a second method for single-site Rydberg addressing in 3D, where a selected target atom can be excited to Rydberg state while preserving the state of any nontarget atom due to a spin echo sequence. The capability to selectively address a target atom in 3D atomic arrays for Rydberg excitation makes it possible to design large-scale neutral-atom information processor based on Rydberg blockade.