arXiv subjects

Igor Aharonovich

Publications and source records attributed to Igor Aharonovich.

At least 109 records · Page 6Linked to original sources

arXiv2021

Bottom-Up Synthesis of Hexagonal Boron Nitride Nanoparticles with Intensity-Stabilized Quantum Emitters

Fluorescent nanoparticles are widely utilized in a large range of nanoscale imaging and sensing applications. While ultra-small nanoparticles (size <10 nm) are highly desirable, at this size range their photostability can be compromised due to effects such as intensity fluctuation and spectral diffusion caused by interaction with surface states. In this letter, we demonstrate a facile, bottom-up technique for the fabrication of sub-10-nm hBN nanoparticles hosting photostable bright emitters via a catalyst-free hydrothermal reaction between boric acid and melamine. We also implement a simple stabilization protocol that significantly reduces intensity fluctuation by ~85% and narrows the emission linewidth by ~14% by employing a common sol-gel silica coating process. Our study advances a promising strategy for the scalable, bottom-up synthesis of high-quality quantum emitters in hBN nanoparticles.

physics.optics↗

arXiv2021

Fabrication of photonic resonators in bulk 4H-SiC

The design and engineering of photonic architectures, suitable to enhance, collect and guide light on chip is needed for applications in quantum photonics and quantum optomechanics. In this work we apply a Faraday cage based oblique angle etch method to fabricate various functional photonic devices from 4H Silicon Carbide - a material that has attracted attention in recent years, due to its potential in optomechanics, nonlinear optics and quantum information. We detail the processing conditions and thoroughly address the geometrical and optical characteristics of the fabricated devices. Employing photoluminescence measurements we demonstrate high quality factors for suspended microring resonators of up to 3500 in the visible range. Such devices will be applicable in the future to augment the properties of SiC in integrated on chip quantum photonics.

physics.optics↗

arXiv2021

Nanofabrication of high Q, transferable, diamond resonators

Advancement of diamond based photonic circuitry requires robust fabrication protocols of key components, including diamond resonators and cavities. Here, we present 1D (nanobeam) photonic crystal cavities generated from single crystal diamond membranes utilising a metallic tungsten layer as a restraining, conductive and removable hard mask. The use of tungsten instead of a more conventional silicon oxide layer enables good repeatability and reliability of the fabrication procedures. The process yields high quality diamond cavities with quality factors (Q factors) approaching 10$^$4. Finally, we show that the cavities can be picked up and transferred onto a trenched substrate to realise fully suspended diamond cavities. Our fabrication process demonstrates the capability of diamond membranes as modular components for broader diamond based quantum photonic circuitry.

physics.optics↗

arXiv2020

Room Temperature Coherent Control of Spin Defects in hexagonal Boron Nitride

Optically active defects in solids with accessible spin states are promising candidates for solid state quantum information and sensing applications. To employ these defects as quantum building blocks, coherent manipulation of their spin state is required. Here we realize coherent control of ensembles of boron vacancy (V$_B^-$) centers in hexagonal boron nitride (hBN). Specifically, by applying pulsed spin resonance protocols, we measure spin-lattice relaxation time ($T_1$) of 18 $μ$s and spin coherence time ($T_2$) of 2 $μ$s at room temperature. The spin-lattice relaxation time increases by three orders of magnitude at cryogenic temperature. Furthermore, employing a two- and three-pulse electron spin-echo envelope modulation (ESEEM) we separate the quadrupole and hyperfine interactions with the surrounding nuclei. Finally, by applying a method to decouple the spin state from its inhomogeneous nuclear environment - a "hole-burning" - the spectral optically detected magnetic resonance linewidth is significantly reduced to several tens of kHz, thus extending the spin coherence time by a factor of three. Our results are important for employment of van der Waals materials for quantum technologies, specifically in the context of using hBN as a high-resolution quantum sensor for hybrid quantum systems including 2D heterostructures, nanoscale devices and emerging atomically thin magnets.

cond-mat.mes-hall↗

arXiv2020

Versatile Direct Writing of Dopants in a Solid State Host Through Recoil Implantation

Modifying material properties at the nanoscale is crucially important for devices in nanoelectronics, nanophotonics and quantum information. Optically active defects in wide band gap materials, for instance, are vital constituents for the realisation of quantum technologies. Yet, the introduction of atomic defects through direct ion implantation remains a fundamental challenge. Herein, we establish a universal method for material doping by exploiting one of the most fundamental principles of physics - momentum transfer. As a proof of concept, we direct-write arrays of emitters into diamond via momentum transfer from a Xe+ focused ion beam (FIB) to thin films of the group IV dopants pre-deposited onto a diamond surface. We conclusively show that the technique, which we term knock-on doping, can yield ultra-shallow dopant profiles localized to the top 5 nm of the target surface, and use it to achieve sub-50 nm lateral resolution. The knock-on doping method is cost-effective, yet very versatile, powerful and universally suitable for applications such as electronic and magnetic doping of atomically thin materials and engineering of near-surface states of semiconductor devices.

physics.app-ph↗

arXiv2020

Optical repumping of resonantly excited quantum emitters in hexagonal boron nitride

Resonant excitation of solid-state quantum emitters enables coherent control of quantum states and generation of coherent single photons, which are required for scalable quantum photonics applications. However, these systems can often decay to one or more intermediate dark states or spectrally jump, resulting in the lack of photons on resonance. Here, we present an optical co-excitation scheme which uses a weak non-resonant laser to reduce transitions to a dark state and amplify the photoluminescence from quantum emitters in hexagonal boron nitride (hBN). Utilizing a two-laser repumping scheme, we achieve optically stable resonance fluorescence of hBN emitters and an overall increase of ON time by an order of magnitude compared to only resonant excitation. Our results are important for the deployment of atom-like defects in hBN as reliable building blocks for quantum photonic applications.

physics.optics↗

arXiv2020

Atomically Thin Boron Nitride as an Ideal Spacer for Metal-Enhanced Fluorescence

The metal-enhanced fluorescence (MEF) considerably enhances the luminescence for various applications, but its performance largely depends on the dielectric spacer between the fluorophore and plasmonic system. It is still challenging to produce a defect-free spacer having an optimized thickness with a subnanometer accuracy that enables reusability without affecting the enhancement. In this study, we demonstrate the use of atomically thin hexagonal boron nitride (BN) as an ideal MEF spacer owing to its multifold advantages over the traditional dielectric thin films. With rhodamine 6G as a representative fluorophore, it largely improves the enhancement factor (up to ~95+-5), sensitivity (10^-8 M), reproducibility, and reusability (~90% of the plasmonic activity is retained after 30 cycles of heating at 350 °C in air) of MEF. This can be attributed to its two-dimensional structure, thickness control at the atomic level, defect-free quality, high affinities to aromatic fluorophores, good thermal stability, and excellent impermeability. The atomically thin BN spacers could increase the use of MEF in different fields and industries.

physics.app-ph↗

arXiv2020

Characterization of single photon sources for radiometry applications at room temperature

A single photon source with high repeatability and low uncertainties is the key element for few-photon metrology based on photon numbers. While low photon number fluctuations and high repeatability are important figures for qualification as a standard light source, these characteristics are limited in single photon emitters by some malicious phenomena like blinking or internal relaxations to varying degrees in different materials. This study seeks to characterize photon number fluctuations and repeatability for radiometry applications at room temperature. For generality in this study, we collected photon statistics data with various single photon emitters of $g^{(2)}(0) < 1$ at low excitation power and room temperature in three material platforms: silicon vacancy in diamond, defects in GaN, and vacancy in hBN. We found common factors related with the relaxation times of the internal states that indirectly affect photon number stability. We observed a high stability of photon number with defects in GaN due to faster relaxations compared with vacancies in hBN, which on the other hand produced high rates ($> 10^6$) of photons per second. Finally, we demonstrate repeatable radiant flux measurements of a bright hBN single photon emitter for a wide radiant flux range from a few tens of femtowatts to one picowatt.

physics.optics↗

arXiv2020

Large few-layer hexagonal boron nitride flakes for nonlinear optics

Hexagonal boron nitride (hBN) is a layered dielectric material with a wide range of applications in optics and photonics. In this work, we demonstrate a fabrication method for few-layer hBN flakes with areas up to 5000 $\rm μm$. We show that hBN in this form can be integrated with photonic microstructures: as an example, we use a circular Bragg grating (CBG). The layer quality of the exfoliated hBN flake on a CBG is confirmed by second-harmonic generation (SHG) microscopy. We show that the SHG signal is uniform across the hBN sample outside the CBG and is amplified in the centre of the CBG.

physics.app-ph↗

arXiv2020

Photoluminescence and photochemistry of the $V_B^-$ defect in hexagonal boron nitride

Extensive photochemical and spectroscopic properties of the $V_B^-$ defect in hexagonal boron nitride are calculated, concluding that the observed photoemission associated with recently observed optically-detected magnetic resonance is most likely of (1)3E" to (1)3A2' origin. Rapid intersystem crossing from the defect's triplet to singlet manifolds explains the observed short excited-state lifetime and very low quantum yield. New experimental results reveal smaller intrinsic spectral bandwidths than previously recognized, interpreted in terms spectral narrowing and zero-phonon-line shifting induced by the Jahn-Teller effect. Different types of computational methods are applied to map out the complex triplet and singlet defect manifolds, including the doubly ionised formulation of the equation-of-motion coupled-cluster theory that is designed to deal with the open-shell nature of defect states, and mixed quantum-mechanics/molecular-mechanics schemes enabling 5763-atom simulations. Two other energetically feasible spectral assignments from amongst the singlet and triplet manifolds are considered, but ruled out based on inappropriate photochemical properties.

cond-mat.mtrl-sci↗

arXiv2020

Tunable quantum photonics platform based on fiber-cavity enhanced single photon emission from two-dimensional hBN

Realization of quantum photonic devices requires coupling single quantum emitters to the mode of optical resonators. In this work we present a hybrid system consisting of defect centers in few-layer hBN grown by chemical vapor deposition and a fiber-based Fabry-Perot cavity. The sub 10 nm thickness of hBN and its smooth surface enables efficient integration into the cavity mode. We operate our hybrid platform over a broad spectral range larger than 30 nm and use its tuneability to explore different coupling regimes. Consequently, we achieve very large cavity-assisted signal enhancement up to 50-fold and equally strong linewidth narrowing owing to cavity funneling, both records for hBN-cavity systems. Additionally, we implement an excitation and readout scheme for resonant excitation that allows us to establish cavity-assisted PLE spectroscopy. Our work marks an important milestone for the deployment of 2D materials coupled to fiber-based cavities in practical quantum technologies.

physics.app-ph↗

arXiv2020

Grain Dependent Growth of Bright Quantum Emitters in Hexagonal Boron Nitride

Point defects in hexagonal boron nitride have emerged as a promising quantum light source due to their bright and photostable room temperature emission. In this work, we study the incorporation of quantum emitters during chemical vapor deposition growth on a nickel substrate. Combining a range of characterization techniques, we demonstrate that the incorporation of quantum emitters is limited to (001) oriented nickel grains. Such emitters display improved emission properties in terms of brightness and stability. We further utilize these emitters and integrate them with a compact optical antenna enhancing light collection from the sources. The hybrid device yields average saturation count rates of ~2.9 x106 cps and an average photon purity of ~90%. Our results advance the controlled generation of spatially distributed quantum emitters in hBN and demonstrate a key step towards on-chip devices with maximum collection efficiency.

physics.app-ph↗

arXiv2020

Valley Polarization Enhancement Induced by a Single Chiral Nanoparticle

Valley polarization is amongst the most critical attributes of atomically thin materials. However, achieving a high contrast from monolayer transition metal dichalcogenides (TMDs) has so far been challenging. In this work, a giant valley polarization contrast up to 45% from a monolayer WS2 has been achieved at room temperature by using a single chiral plasmonic nanoparticle. The increased contrast is attributed to the selective enhancement of both the excitation and the emission rate having one particular handedness of the circular polarization. The experimental results were corroborated by the optical simulation using finite-difference time-domain (FDTD) method. Additionally, the single chiral nanoparticle enabled the observation of valley-polarized luminescence with a linear excitation. Our results provide a promising pathway to enhance valley contrast from monolayer TMDs and utilize them for nanophotonic devices.

physics.app-ph↗

arXiv2020

Identifying Carbon as the Source of Visible Single Photon Emission from Hexagonal Boron Nitride

Single photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered significant attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN and by comparing various synthesis methods, we provide direct evidence that the visible SPEs are carbon related. Room temperature optically detected magnetic resonance (ODMR) is demonstrated on ensembles of these defects. We also perform ion implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of hundreds of potential carbon-based defect transitions suggest that the emission results from the negatively charged VBCN- defect, which experiences long-range out-of-plane deformations and is environmentally sensitive. Our results resolve a long-standing debate about the origin of single emitters at the visible range in hBN and will be key to deterministic engineering of these defects for quantum photonic devices.

physics.app-ph↗

arXiv2020

Engineering spin defects in hexagonal boron nitride

Two-dimensional hexagonal boron nitride offers intriguing opportunities for advanced studies of light-matter interaction at the nanoscale, specifically for realizations in quantum nanophotonics. Here, we demonstrate the engineering of optically-addressable spin defects based on the negatively-charged boron vacancy center. We show that these centers can be created in exfoliated hexagonal boron nitride using a variety of focused ion beams (nitrogen, xenon and argon), with nanoscale precision. Using a combination of laser and resonant microwave excitation, we carry out optically detected magnetic resonance spectroscopy measurements, which reveal a zero-field ground state splitting for the defect of ~3.46 GHz. We also perform photoluminescence excitation spectroscopy and temperature dependent photoluminescence measurements to elucidate the photophysical properties of the center. Our results are important for advanced quantum and nanophotonics realizations involving manipulation and readout of spin defects in hexagonal boron nitride.

physics.app-ph↗

arXiv2020

How to organize an online conference

On January 13th 2020, the inaugural Photonics Online Meetup (POM) brought together more than 1100 researchers to discuss the latest advances in photonics. Or rather, it didn't, because the meeting was completely delocalized with the speakers, organizers, and attendees scattered across six continents and hundreds of locations, connected via a video-conferencing tool and social media. Despite this "delocalisation," the meeting retained many characteristics of a traditional conference: invited and contributed talks with follow-up questions and discussion, and a poster session. However, unlike with traditional conferences, all attendees avoided air travel, high registration costs (it was completely free), CO2 emission, or visa issues. Surely the impact on families was minimized as well, though participants in inconvenient time zones had to wake up early or stay up late. In this Comment, we highlight the key steps that enabled this event, offering tips and advice, to aid the organisation of similar Online Meetups.

cs.CY↗

arXiv2020

Optical Thermometry with Quantum Emitters in Hexagonal Boron Nitride

Nanoscale optical thermometry is a promising non-contact route for measuring local temperature with both high sensitivity and spatial resolution. In this work, we present a deterministic optical thermometry technique based on quantum emitters in nanoscale hexagonal boron-nitride. We show that these nanothermometers exhibit better performance than that of homologous, all-optical nanothermometers both in sensitivity and range of working temperature. We demonstrate their effectiveness as nanothermometers by monitoring the local temperature at specific locations in a variety of custom-built micro-circuits. This work opens new avenues for nanoscale temperature measurements and heat flow studies in miniaturized, integrated devices.

physics.app-ph↗

arXiv2020

Quantum Random Number Generation using a Solid-State Single-Photon Source

Quantum random number generation (QRNG) harnesses the intrinsic randomness of quantum mechanical phenomena. Demonstrations of such processes have, however, been limited to probabilistic sources, for instance, spontaneous parametric down-conversion or faint lasers, which cannot be triggered deterministically. Here, we demonstrate QRNG with a quantum emitter in hexagonal boron nitride; an emerging solid-state quantum source that can generate single photons on demand and operates at room temperature. We achieve true random number generation through the measurement of single photons exiting one of four integrated photonic waveguides, and subsequently, verify the randomness of the sequences in accordance with the National Institute of Standards and Technology benchmark suite. Our results open a new avenue to the fabrication of on-chip deterministic random number generators and other solid-state-based quantum-optical devices.

physics.optics↗