Tunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon.

隧穿是基本的量子过程，没有经典的等效过程，它可以与库仑相互作用竞争，从而产生复杂的现象。可以精确地放置硅中的磷掺杂剂，以解决这种竞争带来的不同状况。然而，他们利用依赖于晶体带对称性的波函数，隧穿相互作用固有地敏感。在这里，我们使用扫描隧道显微镜直接成像硅中耦合原子之间的晶格-非周期性谷干涉。我们的原子分析揭示了包络各向异性，谷值干涉和掺杂剂在海森堡自旋交换相互作用中的作用。我们发现，通过沿特定晶体学方向工程化平面内掺杂剂放置，该交换可以不受谷干扰的影响。恢复了类似真空的行为，其中交换最大化到施主轨道之间的重叠，并且考虑到掺杂剂定位的准确性，成对的对对变化限制为小于10的因数。从与高保真量子计算相关的强库仑相互作用机制到在硅中进行量子仿真的目标耦合强供体阵列，这种鲁棒性在很大的距离范围内均保持不变。