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Single photon interference between bidirectionally extracted photons originating from semiconductor quantum dots
摘要： We report the experimental demonstration of the single-photon interference of bidirectionally extracted photons from epitaxially grown semiconductor quantum dots. The quantum dots were directly connected to single-mode optical fibers. Single-photon nature between transmission and reflection directions was confirmed through detection of antibunching in second-order photon correlation measurements. A Mach–Zehnder interferometer that was naturally formed by introducing the two outputs into a 2 x 2-fiber coupler was used to perform first-order photon correlation measurements.
关键词： single photon interference,single-mode optical fibers,Mach–Zehnder interferometer,semiconductor quantum dots
更新于2025-09-23 15:21:01
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Design for Hybrid Circular Bragg Gratings for a Highly Efficient Quantum-Dot Single-Photon Source
摘要： We present a design for hybrid circular Bragg gratings (hCBGs) for efficiently extracting single-photons emitted by InAs quantum dots (QDs) embedded in GaAs. Finite-difference time-domain simulations show that a very high photon collection efficiency (PCE) up to 96% over a 50 nm bandwidth and pronounced Purcell factors up to 19 at cavity resonance are obtained. We also systematically investigate the geometry parameters, including the SiO2 thickness, grating period, gap width and the central disk radius, to improve the device performances. Finally, the PCEs and the Purcell factors of QDs located at different positions of the hCBG are studied, and the results show great robustness against uncertainties in the location of the QD.
关键词： Semiconductor quantum dots,Circular Bragg gratings,Single-photon source
更新于2025-09-23 15:21:01
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Interaction of ZnO nanorods with plasmonic metal nanoparticles and semiconductor quantum dots
摘要： We model the enhancement of near band edge emission from ZnO nanorods using plasmonic metal nanoparticles and compare it with emission enhancement from ZnO with semiconducting quantum dots. Selected CdSe quantum dots with absorption energies close to those of Ag and Au nanoparticles are chosen to construct model systems with ZnO to comprehend the role of ZnO’s intrinsic defects and plasmonic excitation in realizing the spectrally selective luminescence enhancement. Excitation wavelength dependent photoluminescence spectra along with theoretical models quantifying the related transitions and plasmonic absorption reveal that a complex mechanism of charge transfer between the ZnO nanorods and metal nanoparticles or quantum dots is essential along with an optimal energy band alignment for realizing emission enhancement. The theoretical model presented also provides a direct method of quantifying the relative transition rate constants associated with various electronic transitions in ZnO and their change upon the incorporation of plasmonic nanoparticles. The results indicate that, while the presence of deep level defect states may facilitate the essential charge transfer process between ZnO and the plasmonic nanoparticles, their presence alone does not guarantee UV emission enhancement and strong plasmonic coupling between the two systems. The results offer clues to designing novel multicomponent systems with coupled plasmonic and charge transfer effects for applications in charge localization, energy harvesting, and luminescence enhancement, especially in electrically triggered nanophotonic applications.
关键词： ZnO nanorods,plasmonic metal nanoparticles,semiconductor quantum dots,luminescence enhancement,charge transfer
更新于2025-09-23 15:19:57
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Colloidal Synthesis of Bulk-Bandgap Lead Selenide Nanocrystals
摘要： Lead selenide quantum dots (QDs) are low-bandgap IV-VI semiconducting nanomaterials that have been studied for a variety of applications. Their preparation using colloidal methods can create small spherical to larger cubic nanocrystals, with an upper limit of ～17 nm reported to date. Here we describe methods for preparing cubic PbSe nanocrystals over a 20–40 nm size range using a two-step procedure. Specifically, ～10 nm PbSe QDs are generated using the rapid injection method, the products from which are overcoated with additional lead and selenium precursors. The use of two lead reagents were studied; lead oleate resulted in a maximum of 20 nm cubes, while more reactive lead hexyldecanoate resulted in much larger nanomaterials with bulk bandgaps. However, PbSe samples prepared with lead hexyldecanoate also contained agglomerates. Special care must be taken when characterizing larger strained nanomaterials with X-ray powder diffraction, for which the Scherrer equation is inadequate. A more rigorous approach using the Williamson–Hall method provides characterizations that are consistent with electron microscopy analysis.
关键词： lead selenide,nanomaterials,conductivity,semiconductor,quantum dots
更新于2025-09-19 17:15:36
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Tailored Photoluminescence Properties of Ag(In,Ga)Se <sub/>2</sub> Quantum Dots for Near-Infrared in vivo Imaging
摘要： Multinary semiconductor quantum dots (QDs) that have less toxicity and show near-infrared light responsivity have attracted much attention for in vivo bioimaging. In this study, we controlled the optical properties of Ag-In-Se QDs by modulating the non-stoichiometry and the degree of Ga3+ doping. Precise tuning of the Ag/In ratio of Ag-In-Se QDs enabled a sharp band-edge emission to emerge without broad defect-site emission. Ga3+ doping into Ag-In-Se (AIGSe) QDs enlarged their energy gap, resulting in a blue shift of band-edge PL peak from from 890 to 630 nm. The band-edge PL intensity was remarkably enlarged by surface coating with a thin GaSx shell followed by treatment with trioctylphosphine, the highest PL yield being 38% for the PL peak at 800 nm. Thus-obtained QDs were successfully used as near-IR PL probes for three-dimensional in vivo bio-imaging in which the wavelengths of excitation and detection lights could be selected in the first biological window and then the signals were clearly detected from AIGSe@GaSx core-shell QDs injected into biological tissues by ca. 5 mm in depth.
关键词： I-III-VI2 semiconductor,Quantum dots,Semiconductor nanocrystals,Band-edge emission,Biological imaging,Near-IR photoluminescence
更新于2025-09-19 17:13:59
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An efficient entangled-photon source from semiconductor quantum dots
摘要： Photon entanglement, also known as “Spooky Action at a Distance”, is a promising solution to quantum cryptography and quantum computing. The former will construct a cryptosystem that is impossible to break, and the latter will be capable of solving specific problems much more quickly than any classical computer. An ideal entangled-photon source meeting the following criteria is needed for eventually the practical implementation of quantum information processing: on-demand generation, high-fidelity, ultrabright, high extraction efficiency, and high-temperature operation. For practical applications, it is preferred to have a simple approach that is compatible with current solid-state technologies. Self-organized semiconductor quantum dots (QDs) represent a promising option as an on-demand source of a triggered single-photon and entangled-photon pairs, through the radiative recombination of excitons and biexcitons.
关键词： quantum computing,semiconductor quantum dots,entangled-photon source,quantum cryptography
更新于2025-09-19 17:13:59
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Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise
摘要： The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasistatic noise inherent to any semiconductor device. We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04 (cid:1) 0.23% in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1=f noise observed in isotopically purified silicon qubits.
关键词： gallium arsenide quantum dot,low-frequency noise,Rabi frequency,1=f noise,semiconductor quantum dots,π-flip gate fidelity,isotopically purified silicon qubits,feedback-control technique,high-frequency charge noise,electron spin qubits
更新于2025-09-19 17:13:59
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Nucleation chronology and electronic properties of InAs <sub/>1-x-y</sub> Sb <sub/>x</sub> P <sub/>y</sub> graded composition quantum dots grown on an InAs(100) substrate
摘要： We provide a detailed study of nucleation process, characterization, electronic and optical properties of graded composition quantum dots (GC-QDs) grown from In-As-Sb-P composition liquid phase on an InAs(100) substrate in the Stranski-Krastanov growth mode. Our GCQDs exhibit diameters from 10 to 120 nm and heights from 2 to 20 nm with segregation profiles having a maximum Sb content of approximately 20% at the top and a maximum P content of approximately 15% at the bottom of the GCQDs so that hole confinement is expected in the upper parts of the GCQDs. Using an eight-band k · p model taking strain and built-in electrostatic potentials into account, we have computed the hole ground state energies and charge densities for a wide range of InAs1?x?ySbxPy GCQDs as close as possible to the systems observed in experiment. Finally, we have obtained an absorption spectrum for an ensemble of GCQDs by combining data from both experiment and theory. Excellent agreement between measured and simulated absorption spectra indicates that such GCQDs can be grown following a theory-guided design for application in specific devices.
关键词： absorption spectra,nucleation process,electronic properties,Semiconductor quantum dots,liquid-phase epitaxy,self-assembly
更新于2025-09-19 17:13:59
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Fano resonance induced fast to slow light in a hybrid semiconductor quantum dot and metal nanoparticle system
摘要： We theoretically demonstrate the Fano resonance and the conversion from fast to slow light in a hybrid semiconductor quantum dot (SQDs)-metal nanoparticle (MNPs) with cavity quantum electrodynamics treatment. The absorption spectra of the weak probe field exhibit a series of asymmetric Fano line shapes and their related optical propagation properties, such as fast and slow light effects, are investigated based on the hybrid system for suitable parametric regimes. Further, the transparency windows (i.e. the absorption dip approaches zero) in the probe absorption spectra are accompanied by the rapid steep dispersion of the Fano resonance profile, which promises the slow or fast light effect, and even tunable fast-to-slow light propagation (or vice versa) can be achieved by controlling different parameter regimes. Therefore the investigation may indicate promising applications in quantum information processing based on the hybrid SQD-MNP system.
关键词： semiconductor quantum dots,cavity quantum electrodynamics (C-QED),metal nanoparticles,fast to slow light,Fano resonance
更新于2025-09-16 10:30:52
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Photons and charges from colloidal doped semiconductor quantum dots
摘要： The utility of colloidal semiconductor quantum dots as a source of photons and charge carriers for photonic and photovoltaic applications has created a large field of research focused on tailoring and broadening their functionality beyond what an exciton can provide. One approach towards expanding the range of characteristics of photons and charge carriers from quantum dots is through doping impurity ions (e.g. Mn2+, Cu+, and Yb3+) in the host quantum dots. In addition to the progress in synthesis enabling fine control of the structure of the doped quantum dots, a mechanistic understanding of the underlying processes correlated with the structure has been crucial in revealing the full potential of the doped quantum dots as the source of photons and charge carriers. In this review, we discuss the recent progress made in gaining microscopic understanding of the photophysical pathways that give rise to unique dopant-related luminescence and the generation of energetic hot electrons via exciton-to-hot electron upconversion.
关键词： doping impurity ions,charge carriers,photons,hot electrons,colloidal semiconductor quantum dots,photophysical pathways
更新于2025-09-16 10:30:52