The ability to control phonons in solids is key in many fields of quantum science, ranging from quantum information processing to sensing. Phonons often act as a source of noise and decoherence when solid-state quantum systems interact with the phonon bath of their host matrix. In this study, we demonstrate the ability to control the phononic local density of states of the host matrix using phononic crystals and measure its positive impact on single quantum systems. We design and fabricate diamond phononic crystals with features down to around 20 nm, resulting in a high-frequency complete phononic bandgap from 50 to 70 GHz. The engineered local density of states is probed using single silicon-vacancy colour centres embedded in the phononic crystals. We observe an 18-fold reduction in the phonon-induced orbital relaxation rate of the emitters compared to bulk, thereby demonstrating that the phononic crystal suppresses spontaneous single-phonon processes. Furthermore, we show that our approach can efficiently suppress single-phonon–emitter interactions up to 20 K, allowing the investigation of multi-phonon processes in the emitters. Our results represent an important step towards the realization of efficient phonon–emitter interfaces that can be used for quantum acoustodynamics and quantum phononic networks.

控制固体中声子的能力是量子科学许多领域的关键，从量子信息处理到传感。当固态量子系统与其主矩阵的声子浴相互作用时，声子通常充当噪声和退相干的来源。在这项研究中，我们展示了使用声子晶体控制主矩阵的声子局部状态密度并测量其对单量子系统的积极影响的能力。我们设计和制造具有低至 20 nm 左右特征的金刚石声子晶体，从而产生 50 至 70 GHz 的高频完整声子带隙。使用嵌入声子晶体中的单个硅空位色中心来探测工程化的局部态密度。我们观察到与本体相比，声子诱导的发射器轨道弛豫率降低了 18 倍，从而证明声子晶体抑制了自发的单声子过程。此外，我们表明我们的方法可以有效地抑制高达 20 K 的单声子-发射极相互作用，从而允许研究发射机中的多声子过程。我们的结果代表了朝着实现可用于量子声动力学和量子声子网络的高效声子-发射体界面迈出的重要一步。