Thiago P. Mayer Alegre

Polarization-selective excitation of nitrogen vacancy centers in diamond

The nitrogen vacancy (NV) center in diamond is promising as an electron spin qubit due to its long-lived coherence and optical addressability. The ground state is a spin triplet with two levels

Ultrahigh-Q optomechanical crystal cavities fabricated in a CMOS foundry

({m}_{s}=\ifmmode\pm\else\textpm\fi{}1)

Efficient anchor loss suppression in coupled near-field optomechanical resonators

degenerate at zero magnetic field. Polarization-selective microwave excitation is an attractive method to address the spin transitions independently since this allows operation down to zero magnetic field. Using a resonator designed to produce circularly polarized microwaves, we have investigated the polarization selection rules of the NV center. We first apply this technique to NV ensembles in [100]- and [111]-oriented samples. Next, we demonstrate an imaging technique, based on optical polarization dependence, which allows rapid identification of the orientations of many single NV centers. Finally, we test the microwave polarization selection rules of individual NV centers of known orientation.

Hybrid Confinement Of Optical And Mechanical Modes In A Bullseye Optomechanical Resonator

Photonic crystals use periodic structures to create frequency regions where the optical wave propagation is forbidden, which allows the creation and integration of complex optical functionalities in small footprint devices. Such strategy has also been successfully applied to confine mechanical waves and to explore their interaction with light in the so-called optomechanical cavities. Because of their challenging design, these cavities are traditionally fabricated using dedicated high-resolution electron-beam lithography tools that are inherently slow, limiting this solution to small-scale or research applications. Here we show how to overcome this problem by using a deep-UV photolithography process to fabricate optomechanical crystals in a commercial CMOS foundry. We show that a careful design of the photonic crystals can withstand the limitations of the photolithography process, producing cavities with measured intrinsic optical quality factors as high as Qi = (1.21 ± 0.02) × 106. Optomechanical crystals are also created using phononic crystals to tightly confine the GHz sound waves within the optical cavity, resulting in a measured vacuum optomechanical coupling rate of g0 = 2π × (91 ± 4) kHz. Efficient sideband cooling and amplification are also demonstrated since these cavities are in the resolved sideband regime. Further improvements in the design and fabrication process suggest that commercial foundry-based optomechanical cavities could be used for quantum ground-state cooling.

Theory and Observation of the Brillouin Scattering Self-Cancellation

Elastic dissipation through radiation towards the substrate is a major loss channel in micro- and nanomechanical resonators. Engineering the coupling of these resonators with optical cavities further complicates and constrains the design of low-loss optomechanical devices. In this work we rely on the coherent cancellation of mechanical radiation to demonstrate material and surface absorption limited silicon near-field optomechanical resonators oscillating at tens of MHz. The effectiveness of our dissipation suppression scheme is investigated at room and cryogenic temperatures. While at room temperature we can reach a maximum quality factor of 7.61k (fQ-product of the order of 1011 Hz), at 22 K the quality factor increases to 37k, resulting in a fQ-product of 2 × 1012 Hz.

Brillouin Scattering in Silicon Slot Waveguides

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and applied aspects of the interaction between mechanical and optical waves. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Simulations foresee an optomechanical coupling rate g0 reaching 2π × 100 kHz for mechanical frequencies around 5 GHz as well as anchor loss suppression of 60 dB. Our device design is not limited by unique material properties and could be easily adapted to allow for large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our devices were fabricated in a commercial silicon photonics facility, demonstrating g0/2π = 23 kHz for mechanical modes with frequencies around 2 GHz and mechanical Q-factors as high as 2300 at room temperature, also showing that our approach can be easily scalable and useful as a new platform for multimode optomechanics.

Multi-Ghz Bullseye Optomechanical Cavity

The Brillouin scattering self-cancellation effect arising from the interplay between the photo-elastic and moving-boundary effects is reviewed. Our recent demonstration of this effect for the fundamental Rayleigh acoustic mode in silica nanowires is also discussed.

High Frequency Double-disk Optomechanical Oscillators

Here we numerically investigate Brillouin scattering (BS) in a silicon slot waveguide. We show that BS is strongly influenced by the boundary effects, instead of the usual photo-elastic effect leading to the interaction with distinct mechanical modes.

ERRATA: Optomecânica de microcavidades: do quente ao frio [Physicae 10, 1 (2011)]

We propose a new design for an optomechanical cavity based on a disk with a mechanical radial bandgap. This design allows for independent control of the mechanical and optical frequency and large optomechanical coupling.

Determination of Er-fibre L-band gain coefficient from measured ASE spectra

We propose a double-disk optomechanical resonator with mechanical frequency close to 1 GHz. The design is based on the optimization of the optomechanical interaction of a second-order mechanical mode.