Dissipation dilution enhances SiV coupling to vdW diamond nanomechanics

Abstract

Solid-state color centers embedded into mechanical resonators, where orbital states mediate interactions between spins and long-lived phonons, are a promising platform for hybrid quantum systems. The negatively charged silicon vacancy center in diamond (SiV-) is particularly favorable for strain-coupling to nanomechanical resonators because of its large spin-strain susceptibility and compatibility with device integration. Tensioned nanomechanical resonators offer an attractive route due to their ultra-long mechanical coherence times enabled by diluting defect-induced dissipation, though it is unclear if the same dilution effect undermines strain-mediated coupling to material defect centers. Here, we experimentally demonstrate a tensioned diamond nanobeam platform that enables enhanced strain coupling to SiV- orbital states. Through monitoring the optical response of the SiVs to the static and dynamical strain of the mechanical resonator, we observe that dynamical strain localizes near the clamps of these resonators under static strain. This allows us to enhance SiV-mechanical coupling and the mechanical coherence simultaneously, and provide a SiV-strain sensitivity with greatly improved accuracy over previous literature values. Thus, our work opens a pathway towards seconds-long coherence hybrid quantum systems utilizing point defects in diamond nanomechanics for quantum information processing.

Can dissipation dilution improve mechanical coherence without weakening strain coupling to embedded defects? This paper studies SiV centers in van der Waals self-tensioned diamond nanobeams, using optical spectroscopy to measure static and driven strain responses and interferometry to characterize mechanical motion. Mechanical resonance frequencies calibrate tensile stress, while spectra from small SiV ensembles constrain strain susceptibilities. After correcting for local cross-section variations, a global rescaling of previously reported susceptibilities by $0.356$ fits the static spectra; an independent analysis of published temperature-dependent orbital relaxation gives $0.370$. These results imply roughly threefold smaller coupling rates than predictions using the earlier parameters. Driven optical modulation, calibrated against displacement, shows approximately tenfold greater orbital–phonon coupling near clamps than at beam centers. This is attributed to bending strain localized within a tension-dependent boundary layer. Mechanical quality factors reach $Q_m=2.6\times10^7$, with dilution factors around 30 and inferred intrinsic $Q_{\mathrm{int}}\approx10^6$ at 4 K. Comparison with previous devices finds no measurable implantation-associated degradation. Combined coupling and dilution enhancements yield an estimated thousandfold cooperativity improvement, reaching orbital cooperativity $C_{\mathrm{GS}}\sim100$. The demonstrated coupling is orbital, not a coherent spin–phonon interface: thermal occupation limits quantum cooperativity to approximately $10^{-3}$ at 4 K. Static strain also suppresses spin–strain sensitivity. Alternative clamps that separate static and dynamic strain are simulated, with predicted $g_{\mathrm{spin}}/2\pi\sim1.5$ kHz. Large projected quantum cooperativities require millikelvin operation and assumed spin coherence and mechanical quality factors; preservation of pristine diamond’s ultrahigh low-temperature quality after implantation remains unvalidated.