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Jean Lapointe

Publications and source records attributed to Jean Lapointe.

At least 19 recordsLinked to original sources
arXiv2025

Free space optics in two dimensions: optical elements for silicon photonics without lateral confinement

Silicon photonic components based on freely propagating beams in 220 nm thick Si slab waveguides are described and characterized. Examples include optical relays, waveguide crossings, couplers, and resonators with wavelength independent Q factors. The unconfined beams are manipulated using reflecting mirrors etched into the Si layer, which operate in the total internal reflection (TIR) regime. This approach eliminates the back-scattering and waveguide loss arising from sidewall roughness in single mode waveguides, reduces sensitivity to small dimensional variations, and reduces light induced self-heating. Although the detailed behavior of TIR at curved waveguide side wall mirror is too complex to capture by simple models, the experimental results are found to be in qualitative agreement with simple analytical calculations based on Gaussian beam theory and effective index approximations.

physics.optics↗
arXiv2025

Quantum Emission in Monolayer WSe2 Transferred onto InP Nanowires

Localized quantum emitters in transition-metal dichalcogenides (TMDs) have recently emerged as solid-state candidates for on-demand sources of single photons. Due to the role of strain in the site-selective creation of TMD emitters, their hybrid integration into photonic structures such as cavities and waveguides is possible using pick-and-place methods. Here we investigate quantum emission from a hybrid structure consisting of a monolayer of WSe2 interfaced with horizontally aligned InP nanowires (NWs). Our experiments reveal multiple narrow and bright emission peaks in the 715-785 nm spectral range and g(2)(0) as low as 0.049, indicating strong antibunching and good single photon purity. The faceted nature of III-V NWs provides unique opportunities for strain engineering, including the potential for placement of emitters on the top surface for optimal coupling. Our findings pave the way for realizing hybrid quantum light sources for integrated quantum photonics that could combine III-V quantum dots with TMD emitters into a single platform.

physics.optics↗
arXiv2025

Planar Waveguide Circulating Gaussian Beam Resonators on a Silicon Photonic Chip

A Si slab waveguide resonator design with a circulating Gaussian-like cavity mode is described and characterized, for both all-pass and add-drop configurations and several different input/output coupling strengths. The circulating beam propagates in a slab waveguide with no lateral confinement. Three straight mirrors and one curved mirror define a folded two-dimensional Gaussian cavity. Light is coupled to and from the resonator by beam splitters formed by a narrow gap between a cavity mirror and the input slab waveguides. The coupling is determined by the gap width and is wavelength independent and lossless. For a L=100 um path length cavity, resonance line widths of 5 pm with Q-values of Q = 310000 were measured. The resonator drop spectrum exhibited a comb of almost identical resonance lines across a 100 nm tuning range. This resonator design is capable of broadband operation and is less susceptible to sidewall roughness and defect scattering induced loss and mode splitting, when compared with Si rings formed from narrow single mode waveguides.

physics.optics↗
arXiv2023

On-demand single photon emission in the telecom C-band from nanowire-based quantum dots

Single photon sources operating on-demand at telecom wavelengths are required in fiber-based quantum secure communication technologies. In this work we demonstrate single photon emission from position-controlled nanowire quantum dots emitting at {\lambda} > 1530 nm. Using above-band pulsed excitation, we obtain single photon purities of g(2)(0) = 0.062. These results represent an important step towards the scalable manufacture of high efficiency, high rate single photon emitters in the telecom C-band.

quant-ph↗
arXiv2022

Approaching transform-limited photons from nanowire quantum dots excited above-band

We demonstrate that, even when employing above-band excitation, photons emitted from semiconductor quantum dots can have linewidths that approach their transform-limited values. This is accomplished by using quantum dots embedded in bottom-up photonic nanowires, an approach which mitigates several potential mechanisms that can result in linewidth broadening: (i) only a single quantum dot is present in each device, (ii) dot nucleation proceeds without the formation of a wetting layer, and (iii) the sidewalls of the photonic nanowire are comprised not of etched facets, but of epitaxially grown crystal planes. Using these structures we achieve linewidths of 2x the transform limit, unprecedented for above-band excitation. We also demonstrate a highly nonlinear dependence of the linewidth on both excitation power and temperature which can be described by an independent Boson model that considers both deformation and piezoelectric exciton-phonon coupling. We find that for sufficiently low excitation powers and temperatures, the observed excess broadening is not dominated by phonon dephasing, a surprising result considering the high phonon occupation that occurs with above-band excitation.

cond-mat.mes-hall↗
arXiv2022

Charge detection using a WSe$_2$ van der Waals heterostructure

Detecting single charging events in quantum devices is an important step towards realizing practical quantum circuits for quantum information processing. In this work, we demonstrate that van derWaals heterostructure devices with gated nano-constrictions in monolayer WSe2 can be used as charge detectors for nearby quantum dots. These results open the possibility of implementing charge detection schemes based on 2D materials in complex quantum circuits.

cond-mat.mes-hall↗
arXiv2021

Unity yield of deterministically positioned quantum dot single photon sources

We report on a platform for the production of single photon devices with a fabrication yield of 100%. The sources are based on InAsP quantum dots embedded within position-controlled bottom-up InP nanowires. Using optimized growth conditions, we produce large arrays of structures having highly uniform geometries. Collection efficiencies are as high as 83% and multiphoton emission probabilities as low as 0.6% with the distribution away from optimal values associated with the excitation of other charge complexes and re-excitation processes, respectively, inherent to the above-band excitation employed. Importantly, emission peak lineshapes have Lorentzian profiles indicating that linewidths are not limited by inhomogeneous broadening but rather pure dephasing, likely elastic carrier-phonon scattering due to a high phonon occupation. This work establishes nanowire-based devices as a viable route for the scalable fabrication of efficient single photon sources and provides a valuable resource for hybrid on-chip platforms currently being developed.

quant-ph↗
arXiv2021

Optical fibre-based (plug-and-play) single photon source using InAsP quantum dot nanowires and gradient-index lens collection

We present a compact, fibre-coupled single photon source using gradient-index (GRIN) lenses and an InAsP semiconductor quantum dot embedded within an InP photonic nanowire waveguide. A GRIN lens assembly is used to collect photons close to the tip of the nanowire, coupling the light immediately into a single mode optical fibre. The system provides a stable, high brightness source of fibre-coupled single photons. Using pulsed excitation, we demonstrate on-demand operation with a single photon purity of 98.5% when exciting at saturation in a device with a source-fibre collection efficiency of 35% and an overall single photon collection efficiency of 10%. We also demonstrate "plug and play" operation using room temperature photoluminescence from the InP nanowire for room temperature alignment.

physics.optics↗
arXiv2020

Spectrum-free integrated photonic remote molecular identification and sensing

Absorption spectroscopy is widely used in sensing and astronomy to understand molecular compositions on microscopic to cosmological scales. However, typical dispersive spectroscopic techniques require multichannel detection, fundamentally limiting the ability to detect extremely weak signals when compared to direct photometric methods. We report the realization of direct spectral molecular detection using a silicon nanophotonic waveguide resonator, obviating dispersive spectral acquisition. We use a thermally tunable silicon ring resonator with a transmission spectrum matched and cross-correlated to the quasi-periodic vibronic absorption lines of hydrogen cyanide. We show that the correlation peak amplitude is proportional to the number of overlapping ring resonances and gas lines, and that molecular specificity is obtained from the phase of the correlation signal in a single detection channel. Our results demonstrate on-chip correlation spectroscopy that is less restricted by the signal-to-noise penalty of other spectroscopic approaches, enabling the detection of faint spectral signatures.

physics.ins-det↗
arXiv2018

Monolithic integration of single photon sources via evanescent coupling of tapered InP nanowires to SiN waveguides

We demonstrate a method to monolithically integrate nanowire-based quantum dot single photon sources on-chip using evanescent coupling. By deterministically placing an appropriately tapered III-V nanowire waveguide, containing a single quantum dot, on top of a silicon-based ridge waveguide, the quantum dot emission can be transferred to the ridge waveguide with calculated efficiencies close to 100%. As the evanescent coupling is bidirectional, the source can be optically pumped in both free-space and through the ridge waveguide. The latter onfiguration provides a self-contained, all-fiber, single photon source suitable as a plug-and-play solution for applications requiring bright, on-demand single photons. Using InAsP quantum dots embedded in InP nanowire waveguides, we demonstrate coupling efficiencies to a SiN ridge waveguide of 74% with a single photon purity of 97%.

physics.app-ph↗
arXiv2018

Theory and experiments of coherent photon coupling in semiconductor nanowire waveguides with quantum dot molecules

We present a quantum optics theory, numerical calculations, and experiments on coupled quantumdots in semiconductor nanowire waveguides. We first present an analytical Green function theory tocompute the emitted spectra of two coupled quantum dots, treated as point dipoles, fully accountingfor retardation effects, and demonstrate the signatures of coherent and incoherent coupling througha pronounced splitting of the uncoupled quantum dot resonances and modified spectral broadening.In the weak excitation regime, the classical Green functions used in models are verified and justifiedthrough full 3D solutions of Maxwell equations for nanowire waveguides, specifically using finite-difference time-domain techniques, showing how both waveguide modes and near-field evanescentmode coupling is important. The theory exploits an ensemble-based quantum description, and andan intuitive eigenmode-expansion based Maxwell theory. We then demonstrate how the molecularresonances (in the presence of coupling) take on the form of bright and dark (or quasi-dark) reso-nances, and study how these depend on the excitation and detection conditions. To go beyond theweak excitation regime, we also introduce a quantum master equation approach to model the non-linear spectra from an increasing incoherent pump field, which shows the role of the pump field onthe oscillator strengths and broadening of the molecular resonances, with and without pure dephas-ing. Next, we present experimental photoluminescence spectra for spatially-separated quantum dotmolecules (InAsP) in InP nanowires, which show clear signatures of pronounced splittings, thoughthey also highlight additional mechanisms that are not accounted for in the dipole-dipole couplingmodel. Two different approaches are taken to control the spatial separation of the quantum dotmolecules, and we discuss the advantages and disadvantages of each.

physics.optics↗
arXiv2018

In-situ tuning of individual position-controlled nanowire quantum dots via laser-induced intermixing

We demonstrate an in-situ technique to tune the emission energy of semiconductor quantum dots. The technique is based on laser-induced atomic intermixing applied to nanowire quantum dots grown using a site-selective process that allows for the deterministic tuning of individual emitters. A tuning range of up to 15 meV is obtained with a precision limited by the laser exposure time. A distinct saturation of the energy shift is observed, which suggests an intermixing mechanism relying on grown-in defects that are subsequently removed from the semiconductor material during annealing. The ability to tune different emitters into resonance with each other will be required for fabricating remote quantum dot-based sources of indistinguishable photons for secure quantum networks.

cond-mat.mes-hall↗
arXiv2018

Bright single InAsP quantum dots at telecom wavelengths in position-controlled InP nanowires: the role of the photonic waveguide

We report on the site-selected growth of bright single InAsP quantum dots embedded within InP photonic nanowire waveguides emitting at telecom wavelengths. We demonstrate a dramatic dependence of the emission rate on both the emission wavelength and the nanowire diameter. With an appropriately designed waveguide, tailored to the emission wavelength of the dot, an increase in count rate by nearly two orders of magnitude (0.4kcps to 35kcps) is obtained for quantum dots emitting in the telecom O-band. Using emission-wavelength-optimised waveguides, we demonstrate bright, narrow linewidth emission from single InAsP quantum dots with an unprecedented tuning range from 880nm to 1550nm. These results pave the way towards efficient single photon sources at telecom wavelengths using deterministically grown InAsP/InP nanowire quantum dots.

cond-mat.mes-hall↗
arXiv2017

A solid state source of photon triplets based on quantum dot molecules

Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on single photons and photon pairs, multipartite correlated photon states are usually produced in purely optical systems by post-selection or cascading, with extremely low efficiency and exponentially poor scaling. Multipartite states enable improved tests of the foundations of quantum mechanics as well as implementations of complex quantum optical networks and protocols. It would be favorable to directly generate these states using solid state systems, for better scaling, simpler handling, and the promise of reversible transfer of quantum information between stationary and flying qubits. Here we use the ground states of two optically active coupled quantum dots to directly produce photon triplets. The wavefunctions of photogenerated excitons localized in these ground states are correlated via molecular hybridization and Coulomb interactions. The formation of a triexciton leads to a triple cascade recombination and sequential emission of three photons with strong correlations. The quantum dot molecule is embedded in an epitaxially grown nanowire engineered for single-mode waveguiding and improved extraction efficiency at the emission wavelength. We record 65.62 photon triplets per minute, surpassing rates of all earlier reported sources, in spite of the moderate efficiency of our detectors. Our structure and data represent a breakthrough towards implementing multipartite photon entanglement and multi-qubit readout schemes in solid state devices, suitable for integrated quantum information processing.

quant-ph↗
arXiv2014

Overcoming power broadening of the quantum dot emission in a pure wurtzite nanowire

One of the key challenges in developing quantum networks is to generate single photons with high brightness, purity, and long temporal coherence. Semiconductor quantum dots potentially satisfy these requirements; however, due to imperfections in the surrounding material, the coherence generally degrades with increasing excitation power yielding a broader emission spectrum. Here we overcome this power broadening regime and demonstrate the longest coherence at exciton saturation where the detection count rates are highest. We detect single-photon count rates of 460,000 counts per second under pulsed laser excitation while maintaining a single-photon purity of greater than 99%. Importantly, the enhanced coherence is attained with quantum dots in ultraclean wurtzite InP nanowires, where the surrounding charge traps are filled by exciting above the wurtzite InP nanowire bandgap. By raising the excitation intensity, the number of possible charge configurations in the quantum dot environment is reduced, resulting in a narrower emission spectrum. Via Monte Carlo simulations we explain the observed narrowing of the emission spectrum with increasing power. Cooling down the sample to 300 mK, we further enhance the single-photon coherence two-fold as compared to operation at 4.5 K, resulting in a homogeneous coherence time, T2, of 1.2 ns.

cond-mat.mes-hall↗
arXiv2012

A Semiconductor Under Insulator Technology in Indium Phosphide

This Letter introduces a Semiconductor-Under-Insulator (SUI) technology in InP for designing strip waveguides that interface InP photonic crystal membrane structures. Strip waveguides in InP-SUI are supported under an atomic layer deposited insulator layer in contrast to strip waveguides in silicon supported on insulator. We show a substantial improvement in optical transmission when using InP-SUI strip waveguides interfaced with localized photonic crystal membrane structures when compared with extended photonic crystal waveguide membranes. Furthermore, SUI makes available various fiber-coupling techniques used in SOI, such as sub-micron coupling, for planar membrane III-V systems.

physics.optics↗
arXiv2008

Stability Diagram of a Few-Electron Triple Dot

Quantum dots are considered building blocks for future quantum information circuits. We present here experimental results on a quantum dot circuit consisting of three quantum dots with controlled electron numbers down to one per dot and tunable coupling. We experimentally map out for the first time the stability diagram of the triatomic system and reveal the existence of quadruple points, a signature of the three dots being in resonance. In their vicinity we observe a surprising effect, a 'cloning' of charge transfer transitions related to charge and spin reconfigurations. The experimental results are reproduced by equivalent circuit analysis and Hubbard models.

cond-mat.mes-hall↗