Srujan Meesala

High quality-factor optical nanocavities in bulk single-crystal diamond

Single-crystal diamond, with its unique optical, mechanical and thermal properties, has emerged as a promising material with applications in classical and quantum optics. However, the lack of heteroepitaxial growth and scalable fabrication techniques remains the major limiting factors preventing more wide-spread development and application of diamond photonics. In this work, we overcome this difficulty by adapting angled-etching techniques, previously developed for realization of diamond nanomechanical resonators, to fabricate racetrack resonators and photonic crystal cavities in bulk single-crystal diamond. Our devices feature large optical quality factors, in excess of 105, and operate over a wide wavelength range, spanning visible and telecom. These newly developed high-Q diamond optical nanocavities open the door for a wealth of applications, ranging from nonlinear optics and chemical sensing, to quantum information processing and cavity optomechanics.

A multicolor, broadband (5–20 μm), quaternary-capped InAs/GaAs quantum dot infrared photodetector

An InAs/GaAs quantum dot infrared photodetector with strong, multicolor, broadband (5–20 μm) photoresponse is reported. Using a combined quaternary In0.21Al0.21Ga0.58As and GaAs capping that relieves strain and maintains strong carrier confinement, we demonstrate a four color infrared response with peaks in the midwave- (5.7 μm), longwave- (9.0 and 14.5 μm), and far- (17 μm) infrared regions. Narrow spectral widths (7% to 9%) are noted at each of these wavelengths including responsivity value ∼95.3 mA/W at 14.5 μm. Using strain field and multi-band k⋅p theory, we map specific bound-to-bound and bound-to-quasibound transitions to the longwave and midwave responses, respectively.

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.

Diamond optomechanical crystals

Cavity-optomechanical systems realized in single-crystal diamond are poised to benefit from its extraordinary material properties, including low mechanical dissipation and a wide optical transparency window. Diamond is also rich in optically active defects, such as the nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, which behave as atom-like systems in the solid state. Predictions and observations of coherent coupling of the NV electronic spin to phonons via lattice strain has motivated the development of diamond nanomechanical devices aimed at realization of hybrid quantum systems, in which phonons provide an interface with diamond spins. In this work, we demonstrate diamond optomechanical crystals (OMCs), a device platform to enable such applications, wherein the co-localization of ~ 200 THz photons and few to 10 GHz phonons in a quasi-periodic diamond nanostructure leads to coupling of an optical cavity field to a mechanical mode via radiation pressure. In contrast to other material systems, diamond OMCs operating in the resolved-sideband regime possess large intracavity photon capacity (> 10

Efficient, uniform, and large area microwave magnetic coupling to NV centers in diamond using double split-ring resonators.

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Fiber-Coupled Diamond Quantum Nanophotonic Interface

) and sufficient optomechanical coupling rates to reach a cooperativity of ~ 20 at room temperature, allowing for the observation of optomechanically induced transparency and the realization of large amplitude optomechanical self-oscillations.

Freestanding nanostructures via reactive ion beam angled etching

We report on the development and utilization of a double split-ring microwave resonator for uniform and efficient coupling of microwave magnetic field into nitrogen-vacancy (NV) centers in a diamond over a mm(2) area. Uniformity and magnitude of delivered microwave field were measured using the Rabi nutation experiment on arrays of diamond nanowires with ensemble NV centers. An average Rabi nutation frequency of 15.65 MHz was measured over an area of 0.95 × 1.2 mm, for an input microwave power of 0.5 W. By mapping the Rabi nutation frequency to the magnetic field, the average value of the magnetic field over the aforementioned area and input microwave power was 5.59 G with a standard division of 0.24 G.

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

Color centers in diamond provide a promising platform for quantum optics in the solid state, with coherent optical transitions and long-lived electron and nuclear spins. Building upon recent demonstrations of nanophotonic waveguides and optical cavities in single-crystal diamond, we now demonstrate on-chip diamond nanophotonics with a high efficiency fiber-optical interface, achieving > 90% power coupling at visible wavelengths. We use this approach to demonstrate a bright source of narrowband single photons, based on a silicon-vacancy color center embedded within a waveguide-coupled diamond photonic crystal cavity. Our fiber-coupled diamond quantum nanophotonic interface results in a high, nearly 0.45 MHz, flux of narrowband single photons into a single mode fiber, enabling new possibilities for realizing quantum networks that interface multiple emitters, both on-chip and separated by long distances.

Phonon networks with SiV centers in diamond waveguides

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.

Effects of contact space charge on the performance of quantum intersubband photodetectors

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.