Young-Ik Sohn

Enhanced Strain Coupling of Nitrogen-Vacancy Spins to Nanoscale Diamond Cantilevers

Nitrogen vacancy (NV) centers can couple to confined phonons in diamond mechanical resonators via the effect of lattice strain on their energy levels. Access to the strong spin-phonon coupling regime with this system requires resonators with nanoscale dimensions in order to overcome the weak strain response of the NV ground state spin sublevels. In this work, we study NVs in diamond cantilevers with lateral dimensions of a few hundred nm. Coupling of the NV ground state spin to the mechanical mode is detected in electron spin resonance (ESR), and its temporal dynamics are measured via spin echo. Our small mechanical mode volume leads to a 10-100X enhancement in spin-phonon coupling strength over previous NV-strain coupling demonstrations. This is an important step towards strong spin-phonon coupling, which can enable phonon-mediated quantum information processing and quantum metrology.

Faraday cage angled-etching of nanostructures in bulk dielectrics

For many emerging optoelectronic materials, heteroepitaxial growth techniques do not offer the same high material quality afforded by bulk, single-crystal growth. However, the need for optical, electrical, or mechanical isolation at the nanoscale level often necessitates the use of a dissimilar substrate, upon which the active device layer stands. Faraday cage angled-etching (FCAE) obviates the need for these planar, thin-film technologies by enabling in situ device release and isolation through an angled-etching process. By placing a Faraday cage around the sample during inductively coupled plasma reactive ion etching, the etching plasma develops an equipotential at the cage surface, directing ions normal to its face. In this article, the effects that Faraday cage angle, mesh size, and sample placement have on etch angle, uniformity, and mask selectivity are investigated within a siliconetching platform. Simulation results qualitatively confirm experiments and help to clarify the physical mechanisms at work. These results will help guide FCAE process design across a wide range of material platforms.

Dynamic actuation of single-crystal diamond nanobeams

We show the dielectrophoretic actuation of single-crystal diamond nanomechanical devices. Gradient radio-frequency electromagnetic forces are used to achieve actuation of both cantilever and doubly clamped beam structures, with operation frequencies ranging from a few MHz to ∼50 MHz. Frequency tuning and parametric actuation are also studied.

Freestanding nanostructures via reactive ion beam angled etching

Freestanding nanostructures play an important role in optical and mechanical devices for classical and quantum applications. Here, we use reactive ion beam angled etching to fabricate optical resonators in bulk polycrystalline and single crystal diamond. Reported quality factors are approximately 30 000 and 286 000, respectively. The devices show uniformity across 25 mm samples, a significant improvement over comparable techniques yielding freestanding nanostructures.

Controlling the coherence of a diamond spin qubit through its strain environment

The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. For quantum bits in the solid state, decoherence from thermal vibrations of the surrounding lattice can typically only be suppressed by lowering the temperature of operation. Here, we use a nano-electro-mechanical system to mitigate the effect of thermal phonons on a spin qubit – the silicon-vacancy colour centre in diamond – without changing the system temperature. By controlling the strain environment of the colour centre, we tune its electronic levels to probe, control, and eventually suppress the interaction of its spin with the thermal bath. Strain control provides both large tunability of the optical transitions and significantly improved spin coherence. Finally, our findings indicate the possibility to achieve strong coupling between the silicon-vacancy spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics.Silicon-vacancy centres in diamond are promising candidates as emitters in photonic quantum networks, but their coherence is degraded by large electron-phonon interactions. Sohn et al. demonstrate the use of strain to tune a silicon vacancy’s electronic structure and suppress phonon-mediated decoherence.

Novel fabrication of diamond nanophotonics coupled to single-photon detectors

Diamond nanophotonics is a rapidly evolving platform in which non-classical light—emitted by defect centers in diamond— can be generated, manipulated, and detected in a single monolithic device (e.g., for quantum information processing applications).1–3 Indeed, novel diamond fabrication techniques make it possible to engineer unique nanostructures in which diamond’s extraordinary material properties (e.g., high refractive index, wide band gap, and large optical transmission window) can be exploited.4, 5 The relatively large Kerr non-linearity6 of diamond also makes it an attractive platform for on-chip nonlinear optics at visible and IR wavelengths.7 This nonlinearity could be used for frequency conversion of photons generated by color centers in diamond (i.e., from their typical visible wavelengths to telecom wavelengths).8 In turn, this would enable transmission of quantum information and distribution of quantum entanglement9, 10 over long distances. Such integrated diamond–quantum photonics platforms would benefit from the use (and realization) of high-performance single-photon detectors that have broadband photon sensitivity and are integrated on the same diamond chip. Superconducting nanowire single-photon detectors (SNSPDs) are a class of cutting-edge photon detectors that outperform other technologies in terms of detection efficiency, dark counts, timing jitter, and maximum count rates.11–13 SNSPDs typically consist of narrow nanowires that are patterned into an ultrathin (4–8nm) superconducting film.14 The nanowires are biased close to the critical current of the superconductor material so that Figure 1. Confocal scan of freestanding diamond waveguides, where bright spots indicate locations of implanted single nitrogen vacancy centers.

Mechanical and optical nanodevices in single-crystal quartz

Single-crystal {\alpha}-quartz, one of the most widely used piezoelectric materials, has enabled a wide range of timing applications. Owing to the fact that integrated thin-film based quartz platform is not available, most of these applications rely on macroscopic, bulk crystal-based devices. Here we show that the Faraday cage angled-etching technique can be used to realize nanoscale electromechanical and photonic devices in quartz. Using this approach, we demonstrate quartz nanomechanical cantilevers and ring resonators featuring Qs of 4,900 and 8,900, respectively.