Controlling all Degrees of Freedom of the Optical Coupling in Hybrid Quantum Photonics

Nanophotonic quantum devices can significantly boost light-matter interaction which is important for applications such as quantum networks. Reaching a high interaction strength between an optical transition of a spin system and a single mode of light is an essential step which demands precise control over all degrees of freedom of the optical coupling. While current devices have reached a high accuracy of emitter positioning, the placement process remains overall statistically, reducing the device fabrication yield. Furthermore, not all degrees of freedom of the optical coupling can be controlled limiting the device performance. Here, we develop a hybrid approach based on negatively-charged silicon-vacancy center in nanodiamonds coupled to a mode of a Si$_3$N$_4$-photonic crystal cavity, where all terms of the coupling strength can be controlled individually. We use the frequency of coherent Rabi-oscillations and line-broadening as a measure of the device performance. This allows for iterative optimization of the position and the rotation of the dipole with respect to individual, preselected modes of light. Therefore, our work marks an important step for optimization of hybrid quantum photonics and enables to align device simulations with real device performance.Comment: 20 pages, 7 figure

Opto-Mechanical Manipulation Of Molecules And Chemical Reactions

We developed optical methods to manipulate molecules in a microfluidic environment. Optical tweezers can manipulate micro-spheres in solutions with the gradient force but are not practical for spheres smaller than 500 nm in diameter. Nanotweezers use the evanescent field out of waveguides, slot-waveguides, plasmonic resonances, and photonic crystal resonators. They were able to manipulate objects down to 40 nm. Proteins and many biomolecules are of sizes on the order of a few nanometers, a priori out of reach of these techniques. During my PhD, I developed nanophotonic and nano-optic systems aimed at applying electromagnetic potential wells to bias the motion of molecules against Brownian motion and eventually demonstrated that chemical reaction pathways could also be altered. I showed that photonic crystal resonators are a toolbox for nanoscale assembly enabling trapping, transport, and orientation of nano-objects. I also investigated the heat arising in optofluidic photonic crystals and found it to be higher than previously thought, up to 57 K for 10 mW of power input, which makes such devices incompatible with biological single molecule experiments. I then used electromagnetic fields shaped by waveguides-carbon nanotubes hybrids to trap immunoglobulin of mass down to 160 kDa. Last, I developed the optical manipulation of chemical reactions. I showed that electromagnetic gradient force can transport molecules across reaction barriers along a reaction coordinate demonstrating it experimentally by guiding the adsorption of immunoglobulin proteins onto carbon nanotubes. These techniques are part of a wider evolution that is changing the way we interact with molecules. Although originally dismissed for studying single molecules because of the diffraction limit, nano-optics and nanophotonics are becoming the center of this revolution

Multipath trapping dynamics of nanoparticles towards an integrated waveguide with a high index contrast

Optical trapping and manipulation of nanoparticles in integrated photonics devices have recently received increasingly more attention and greatly facilitated the advances in lab-on-chip technologies. In this work, by solving motion equation numerically, we study the trapping dynamics of a nanoparticle near a high-index-contrast slot waveguide, under the influence of water flow perpendicular to the waveguide. It is shown that a nanoparticle can go along different paths before it gets trapped, strongly depending on its initial position relative to the integrated waveguide. Due to localized optical field enhancement on waveguide sidewalls, there are multiple trapping positions, with a critical area where particle trapping and transport are unstable. As the water velocity increases, the effective trapping range shrinks, but with a rate that is smaller than the increasing of water velocity. Finally, the trapping range is shown to decrease for smaller slot width that is below 100 nm, even though smaller slot width generates stronger local optical force

Investigating the use of a hybrid plasmonic–photonic nanoresonator for optical trapping using finite-difference time-domain method

We investigate the use of a hybrid nanoresonator comprising a photonic crystal (PhC) cavity coupled to a plasmonic bowtie nanoantenna (BNA) for the optical trapping of nanoparticles in water. Using finite difference time-domain simulations, we show that this structure can confine light to an extremely small volume of ~30,000 nm3 (~30 zl) in the BNA gap whilst maintaining a high quality factor (5400–7700). The optical intensity inside the BNA gap is enhanced by a factor larger than 40 compared to when the BNA is not present above the PhC cavity. Such a device has potential applications in optical manipulation, creating high precision optical traps with an intensity gradient over a distance much smaller than the diffraction limit, potentially allowing objects to be confined to much smaller volumes and making it ideal for optical trapping of Rayleigh particles (particles much smaller than the wavelength of light)

Bio-molecular applications of recent developments in optical tweezers

In the past three decades, the ability to optically manipulate biomolecules has spurred a new era of medical and biophysical research. Optical tweezers (OT) have enabled experimenters to trap, sort, and probe cells, as well as discern the structural dynamics of proteins and nucleic acids at single molecule level. The steady improvement in OT\u2019s resolving power has progressively pushed the envelope of their applications; there are, however, some inherent limitations that are prompting researchers to look for alternatives to the conventional techniques. To begin with, OT are restricted by their one-dimensional approach, which makes it difficult to conjure an exhaustive three-dimensional picture of biological systems. The high-intensity trapping laser can damage biological samples, a fact that restricts the feasibility of in vivo applications. Finally, direct manipulation of biological matter at nanometer scale remains a significant challenge for conventional OT. A significant amount of literature has been dedicated in the last 10 years to address the aforementioned shortcomings. Innovations in laser technology and advances in various other spheres of applied physics have been capitalized upon to evolve the next generation OT systems. In this review, we elucidate a few of these developments, with particular focus on their biological applications. The manipulation of nanoscopic objects has been achieved by means of plasmonic optical tweezers (POT), which utilize localized surface plasmons to generate optical traps with enhanced trapping potential, and photonic crystal optical tweezers (PhC OT), which attain the same goal by employing different photonic crystal geometries. Femtosecond optical tweezers (fs OT), constructed by replacing the continuous wave (cw) laser source with a femtosecond laser, promise to greatly reduce the damage to living samples. Finally, one way to transcend the one-dimensional nature of the data gained by OT is to couple them to the other large family of single molecule tools, i.e., fluorescence-based imaging techniques. We discuss the distinct advantages of the aforementioned techniques as well as the alternative experimental perspective they provide in comparison to conventional OT

Multiplexed long-range electrohydrodynamic transport and nano-optical trapping with cascaded bowtie photonic crystal cavities

Photonic crystal cavities have been widely studied for optical trapping due to their ability to generate high quality factor resonances. However, prior photonic crystal nanotweezers possess mode volumes significantly larger than those of plasmonic nanotweezers, which limit the gradient force. Additionally, they also suffer from low particle capture rates. In this paper, we propose a nanotweezer system based on a 1D bowtie photonic crystal nanobeam that achieves extreme mode confinement and an electromagnetic field enhancement factor of 68 times, while supporting a high-quality factor of 15,000 in water. Furthermore, by harnessing the localized heating of a water layer near the bowtie cavity region, combined with an applied alternating current electric field, our system provides long-range transport of particles with average velocities of 5 ${\mu}$m/s towards the bowtie cavities on demand. Once transported to the bowtie cavity region, our results show that a 20 nm quantum dot will be confined in a potential well with a depth of 35 ${k_B}$T. Thus, our approach effectively addresses the challenge of limited capture rate in photonic crystal nanotweezers for the first time. Finally, we present the concept of multiplexed long-range transport for hand-off of a single emitter from one cavity to the next by simply switching the wavelength of the input light. This novel multiplexed integrated particle trapping platform is expected to open new opportunities in directed assembly of nanoscale quantum emitters and ultrasensitive sensors for single particle spectroscopy.Comment: 11 pages, 4 figure