Heterogeneous integration of single InAs/InP quantum dots with the SOI chip using direct bonding.

Quantum information processing with photons in small-footprint and highly integrated silicon-based photonic chips requires incorporating non-classical light sources. In this respect, self-assembled III-V semiconductor quantum dots (QDs) are an attractive solution, however, they must be combined with the silicon platform. Here, by utilizing the large-area direct bonding technique, we demonstrate the hybridization of InP and SOI chips, which allows for coupling single photons to the SOI chip interior, offering cost-effective scalability in setting up a multi-source environment for quantum photonic chips. We fabricate devices consisting of self-assembled InAs QDs embedded in the tapered InP waveguide (WG) positioned over the SOI-defined Si WG. Focusing on devices generating light in the telecom C-band compatible with the low-loss optical fiber networks, we demonstrate the light coupling between InP and SOI platforms by observing photons outcoupled at the InP-made circular Bragg grating outcoupler fabricated at the end of an 80 µm-long Si WG, and at the cleaved edge of the Si WG. Finally, for a device with suppressed multi-photon generation events exhibiting 80% single photon generation purity, we measure the photon number outcoupled at the cleaved facet of the Si WG. We estimate the directional on-chip photon coupling between the source and the Si WG to 5.1%.

Temperature dependence of refractive indices of Al0.9Ga0.1As and In0.53Al0.1Ga0.37As in the telecommunication spectral range.

In this work, we determine the temperature dependence of refractive indices of In0.53Al0.1Ga0.37As and Al0.9Ga0.1As semiconductor alloys at telecommunication wavelengths in the range from room temperature down to 10 K. For that, we measure the temperature-dependent reflectance of two structures: with an Al0.9Ga0.1As/GaAs distributed Bragg reflector (DBR) designed for 1.3 µm and with an In0.53Al0.1Ga0.37As/InP DBR designed for 1.55 µm. The obtained experimental results are compared to DBR reflectivity spectra calculated within the transfer matrix method to determine refractive index values. We further show that changes due to the thermal expansion of the DBR layers are negligible for our method.

Spin memory effect in charged single telecom quantum dots: erratum.

This erratum corrects the value of the wetting layer thickness provided in our Article [Opt. Express29, 34024 (2021)10.1364/OE.438708]. This misprint does not influence the results and conclusions presented in the original Article.

Spin memory effect in charged single telecom quantum dots.

Single InP-based quantum dots emitting in the third telecom window are probed quasi-resonantly in polarization-resolved microphotoluminescence experiments. For charged quantum dots we observe negative circular polarization being a fingerprint of the optical spin writing of the carriers within the quantum dots. The investigated quantum dots have a very dense ladder of excited states providing relatively easy quasi-resonant optical excitation, and together with telecom wavelengths emission they bring quantum gates and memories closer to compatibility with fiber-optic communication.

Method for direct coupling of a semiconductor quantum dot to an optical fiber for single-photon source applications.

We present an effective method for direct fiber coupling of a quantum dot (QD) that is deterministically incorporated into a cylindrical mesa. For precise positioning of the fiber with respect to the QD-mesa, we use a scanning procedure relying on interference of light reflected back from the fiber end-face and the top surface of the mesa, applicable for both single-mode and multi-mode fibers. The central part of the fiber end-face is etched to control the required distance between the top surface of the mesa and the fiber core. Emission around 1260 nm from a fiber-coupled InGaAs/GaAs QD is demonstrated and its stability is proven over multiple cooling cycles. Moreover, a single photon character of emission from such system for a line emitting above 1200 nm is proven experimentally by photon autocorrelation measurements with an obtained value of the second order correlation function at zero time-delay well below 0.5.

Zincblende InAsxP1-x/InP Quantum Dot Nanowires for Telecom Wavelength Emission.

InAsxP1-x quantum dots (QDs) in InP nanowires (NWs) have been realized as a platform for emission at telecom wavelengths. These QDs are typically grown in NWs with the wurtzite crystal phase, but in this case, ultrathin diameters are required to achieve defect-free heterostructures, making the structures less robust. In this work, we demonstrate the growth of pure zincblende InAsxP1-x QDs in InP NWs, which enabled an increase in NW diameters to about 45 nm, achieved by employing Au-assisted vapor liquid solid growth in a chemical beam epitaxy system. We studied the growth of InP/InAsxP1-x heterostructures with different compositions to control the straight growth along the ⟨100⟩ direction and to tune the emission wavelength. Interestingly, we found that the growth mechanism for pure InAs QDs is different compared to that for InAsxP1-x alloy QDs. This allowed us to optimize different growth protocols to achieve straight growth of the final QD NWs. We successfully obtained the growth of InAsxP1-x QDs with a composition in the range of x = 0.24-1.00. By means of microphotoluminescence measurements, we demonstrate the tunability of the emission in dependence of the InAsxP1-x QD composition and morphology, remarkably observing an emission at the telecom O-band for a 10 nm thick QD with 80% of As content.

High-throughput quantum photonic devices emitting indistinguishable photons in the telecom C-band.

Single indistinguishable photons at telecom C-band wavelengths are essential for quantum networks and the future quantum internet. However, high-throughput technology for single-photon generation at 1550 nm remained a missing building block to overcome present limitations in quantum communication and information technologies. Here, we demonstrate the high-throughput fabrication of quantum-photonic integrated devices operating at C-band wavelengths based on epitaxial semiconductor quantum dots. Our technique enables the deterministic integration of single pre-selected quantum emitters into microcavities based on circular Bragg gratings. Respective devices feature the triggered generation of single photons with ultra-high purity and record-high photon indistinguishability. Further improvements in yield and coherence properties will pave the way for implementing single-photon non-linear devices and advanced quantum networks at telecom wavelengths.

On-Demand Generation of Indistinguishable Photons in the Telecom C-Band Using Quantum Dot Devices.

Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, which are useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550 nm is ideal. The direct generation of QD-photons in this spectral range with high quantum-optical quality, however, remained challenging. Here, we demonstrate the coherent on-demand generation of indistinguishable photons in the telecom C-band from single QD devices consisting of InAs/InP QD-mesa structures heterogeneously integrated with a metallic reflector on a silicon wafer. Using pulsed two-photon resonant excitation of the biexciton-exciton radiative cascade, we observe Rabi rotations up to pulse areas of 4π and a high single-photon purity in terms of g(2)(0) = 0.005(1) and 0.015(1) for exciton and biexciton photons, respectively. Applying two independent experimental methods, based on fitting Rabi rotations in the emission intensity and performing photon cross-correlation measurements, we consistently obtain preparation fidelities at the π-pulse exceeding 80%. Finally, performing Hong-Ou-Mandel-type two-photon interference experiments, we obtain a photon-indistinguishability of the full photon wave packet of up to 35(3)%, representing a significant advancement in the photon-indistinguishability of single photons emitted directly in the telecom C-band.

Bright Quantum Dot Single-Photon Emitters at Telecom Bands Heterogeneously Integrated on Si.

Whereas the Si photonic platform is highly attractive for scalable optical quantum information processing, it lacks practical solutions for efficient photon generation. Self-assembled semiconductor quantum dots (QDs) efficiently emit photons in the telecom bands (1460-1625 nm) and allow for heterogeneous integration with Si. In this work, we report on a novel, robust, and industry-compatible approach for achieving single-photon emission from InAs/InP QDs heterogeneously integrated with a Si substrate. As a proof of concept, we demonstrate a simple vertical emitting device, employing a metallic mirror beneath the QD emitter, and experimentally obtained photon extraction efficiencies of ∼10%. Nevertheless, the figures of merit of our structures are comparable with values previously only achieved for QDs emitting at shorter wavelength or by applying technically demanding fabrication processes. Our architecture and the simple fabrication procedure allows for the demonstration of high-purity single-photon generation with a second-order correlation function at zero time delay, g (2)(τ = 0) < 0.02, without any corrections at continuous wave excitation at the liquid helium temperature and preserved up to 50 K. For pulsed excitation, we achieve the as-measured g (2)(0) down to 0.205 ± 0.020 (0.114 ± 0.020 with background coincidences subtracted).

Magneto-Optical Characterization of Trions in Symmetric InP-Based Quantum Dots for Quantum Communication Applications.

Magneto-optical parameters of trions in novel large and symmetric InP-based quantum dots, uncommon for molecular beam epitaxy-grown nanostructures, with emission in the third telecom window, are measured in Voigt and Faraday configurations of an external magnetic field. The diamagnetic coefficients are found to be in the range of 1.5-4 µeV/T2, and 8-15 µeV/T2, respectively out-of-plane and in-plane of the dots. The determined values of diamagnetic shifts are related to the anisotropy of dot sizes. Trion g-factors are measured to be relatively small, in the range of 0.3-0.7 and 0.5-1.3, in both configurations, respectively. Analysis of single carrier g-factors, based on the formalism of spin-correlated orbital currents, leads to similar values for hole and electron of ~0.25 for Voigt and ge ≈ -5; gh ≈ +6 for Faraday configuration of the magnetic field. Values of g-factors close to zero measured in Voigt configuration make the investigated dots promising for electrical tuning of the g-factor sign, required for schemes of single spin control in qubit applications.

Metamorphic Buffer Layer Platform for 1550 nm Single-Photon Sources Grown by MBE on (100) GaAs Substrate.

We demonstrate single-photon emission with a low probability of multiphoton events of 5% in the C-band of telecommunication spectral range of standard silica fibers from molecular beam epitaxy grown (100)-GaAs-based structure with InAs quantum dots (QDs) on a metamorphic buffer layer. For this purpose, we propose and implement graded In content digitally alloyed InGaAs metamorphic buffer layer with maximal In content of 42% and GaAs/AlAs distributed Bragg reflector underneath to enhance the extraction efficiency of QD emission. The fundamental limit of the emission rate for the investigated structures is 0.5 GHz based on an emission lifetime of 1.95 ns determined from time-resolved photoluminescence. We prove the relevance of a proposed technology platform for the realization of non-classical light sources in the context of fiber-based quantum communication applications.

InP-Substrate-Based Quantum Dashes on a DBR as Single-Photon Emitters at the Third Telecommunication Window.

We investigated emission properties of photonic structures with InAs/InGaAlAs/InP quantum dashes grown by molecular beam epitaxy on a distributed Bragg reflector. In high-spatial-resolution photoluminescence experiment, well-resolved sharp spectral lines are observed and single-photon emission is detected in the third telecommunication window characterized by very low multiphoton events probabilities. The photoluminescence spectra measured on simple photonic structures in the form of cylindrical mesas reveal significant intensity enhancement by a factor of 4 when compared to a planar sample. These results are supported by simulations of the electromagnetic field distribution, which show emission extraction efficiencies even above 18% for optimized designs. When combined with relatively simple and undemanding fabrication approach, it makes this kind of structures competitive with the existing solutions in that spectral range and prospective in the context of efficient and practical single-photon sources for fiber-based quantum networks applications.

Optical Quality of InAs/InP Quantum Dots on Distributed Bragg Reflector Emitting at 3rd Telecom Window Grown by Molecular Beam Epitaxy.

We present an experimental study on the optical quality of InAs/InP quantum dots (QDs). Investigated structures have application relevance due to emission in the 3rd telecommunication window. The nanostructures are grown by ripening-assisted molecular beam epitaxy. This leads to their unique properties, i.e., low spatial density and in-plane shape symmetry. These are advantageous for non-classical light generation for quantum technologies applications. As a measure of the internal quantum efficiency, the discrepancy between calculated and experimentally determined photon extraction efficiency is used. The investigated nanostructures exhibit close to ideal emission efficiency proving their high structural quality. The thermal stability of emission is investigated by means of microphotoluminescence. This allows to determine the maximal operation temperature of the device and reveal the main emission quenching channels. Emission quenching is predominantly caused by the transition of holes and electrons to higher QD's levels. Additionally, these carriers could further leave the confinement potential via the dense ladder of QD states. Single QD emission is observed up to temperatures of about 100 K, comparable to the best results obtained for epitaxial QDs in this spectral range. The fundamental limit for the emission rate is the excitation radiative lifetime, which spreads from below 0.5 to almost 1.9 ns (GHz operation) without any clear spectral dispersion. Furthermore, carrier dynamics is also determined using time-correlated single-photon counting.

Thermal stability of emission from single InGaAs/GaAs quantum dots at the telecom O-band.

Single-photon sources are key building blocks in most of the emerging secure telecommunication and quantum information processing schemes. Semiconductor quantum dots (QD) have been proven to be the most prospective candidates. However, their practical use in fiber-based quantum communication depends heavily on the possibility of operation in the telecom bands and at temperatures not requiring extensive cryogenic systems. In this paper we present a temperature-dependent study on single QD emission and single-photon emission from metalorganic vapour-phase epitaxy-grown InGaAs/GaAs QDs emitting in the telecom O-band at 1.3 µm. Micro-photoluminescence studies reveal that trapped holes in the vicinity of a QD act as reservoir of carriers that can be exploited to enhance photoluminescence from trion states observed at elevated temperatures up to at least 80 K. The luminescence quenching is mainly related to the promotion of holes to higher states in the valence band and this aspect must be primarily addressed in order to further increase the thermal stability of emission. Photon autocorrelation measurements yield single-photon emission with a purity of [Formula: see text] up to 50 K. Our results imply that these nanostructures are very promising candidates for single-photon sources at elevated (e.g., Stirling cryocooler compatible) temperatures in the telecom O-band and highlight means for improvements in their performance.

Recent developments in cholinesterases inhibitors for Alzheimer's disease treatment.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the central nervous system (CNS) which is the most common cause of dementia in the elderly. It is characterized by the deficits in the cholinergic system and presence of characteristic hallmarks: neurofibrillary tangles and amyloid plaques. Since the cholinergic system plays an important role in the regulation of learning and memory processes it became a target for the design of anti-alzheimer drugs. Cholinesterase inhibitors enhance cholinergic transmission indirectly, by inhibiting the enzyme which hydrolyses acetylcholine. It has been also demonstrated that acetylcholinesterase (AChE) is involved in the development of amyloid plaques. Therefore, substances which are AChE inhibitors (AChEI) are the only drugs approved for the symptomatic treatment of AD. This review presents the main classes of cholinesterase inhibitors developed recently for the treatment of AD. We have started with the analogues of the existing drugs: tacrine, donepezil, rivastigmine and galantamine which are still of interest for many research groups. Among them there is a very interesting group--dual binding site inhibitors characterized by increased inhibitory potency against AChE and amyloid plaques formation. There is also a group of compounds with additional properties such as: antioxidant activity, affinity to 5-HT(3) receptors, inhibition of N-methyltransferase that metabolize histamine, which can be beneficial for the treatment of AD. Furthermore there are some interesting compounds which belong to different chemical groups also of natural origin. In this review we sum up current research concerned with development of AChEIs which can be more effective in the future treatment of AD.

Design, synthesis and pharmacological evaluation of alpha-substituted N-benzylamides of gamma-hydroxybutyric acid with potential GABA-ergic activity. Part 6. Search for new anticonvulsant compounds.

In the recent study we have extended our investigations to the new anticonvulsant derivatives of alpha-substituted N-benzylamides of gamma-hydroxybutyric acid (GHB). Among the obtained compounds N-benzylamide of alpha-(1,2,3,4-tetrahydroisoquinoline)-GHB (9) has demonstrated activity against maximal electroshock (MES) induced seizures in mice (at 100 mg/kg ip) and in rats (at 30 mg/kg, po dose). Lactone 8 and amide 9 have possessed a weak effect on [3H]-muscimol binding. Molecular modeling studies have revealed that anticonvulsant activity of the alpha-substituted amides of GHB might partially be explained by the orientation of the terminal benzylamide fragment.

Synthesis of novel N-alkyl carbamates of a-substituted amides of g-hydroxybutyric acid as potential acetylcholinesterase inhibitors.

In a search for new acetylcholinesterase (AChE) inhibitors, derivatives of N-alkyl carbamates of a-substituted N-benzylamides of g-hydroxybutyric acid (GHB) 2(a-d); 3(a-d); 4(a-d) were obtained. Starting from 3-bromo-tetrahydrofuran-2-one, and N-phenylpiperazine 3-(4-phenylpiperazin-1-yl) tetrahydrofuran-2-one (1) was obtained. The aminolysis of lactone 1 with 4-substituted derivatives of benzylamine yielded N-substituted benzylamides of a-(4-phenylpiperazin-1-yl)-g-hydroxy-butyric acid (2-4). The target compounds were prepared by refluxing N-substituted benzyl-amides of a-(4-phenylpiperazinyl-1-)-GHB with ethyl-, i-propyl-, n-propyl- or n-butyl-isocyanate in dry acetonitrile. The inhibitory potency of AChE was evaluated by means of Ellman's in vitro test.