The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots(SQDs) to raise the growth repeatability.Here,through many growth tests on rotating substrates,we...The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots(SQDs) to raise the growth repeatability.Here,through many growth tests on rotating substrates,we develop a proper In deposition amount(θ) for SQD growth,according to the measured critical θ for test QD nucleation(θ;).The proper ratio θ/θ;,with a large tolerance of the variation of the real substrate temperature(T;),is 0.964-0.971 at the edge and> 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer,and around 0.9709 but < 0.9714 in the center of a 1/4-piece N;wafer as shown in the evolution of QD size and density as θ/θ;varies.Bright SQDs with spectral lines at 905 nm-935 nm nucleate at the edge and correlate with individual 7 nm-8 nm-height QDs in atomic force microscopy,among dense 1 nm-5 nm-height small QDs with a strong spectral profile around 860 nm-880 nm.The higher T;in the center forms diluter,taller and uniform QDs,and very dilute SQDs for a proper θ/θ;:only one 7-nm-height SQD in25 μm;.On a 2-inch(1 inch = 2.54 cm) semi-insulating wafer,by using θ/θ;= 0.961,SQDs nucleate in a circle in 22%of the whole area.More SQDs will form in the broad high-T;region in the center by using a proper θ/θ;.展开更多
We report here a nanostructure that traps single quantum dots for studying strong cavity-emitter coupling. The nanostructure is designed with two elliptical holes in a thin silver patch and a slot that connects the ho...We report here a nanostructure that traps single quantum dots for studying strong cavity-emitter coupling. The nanostructure is designed with two elliptical holes in a thin silver patch and a slot that connects the holes. This structure has two functionalities:(1) tweezers for optical trapping;(2) a plasmonic resonant cavity for quantum electrodynamics. The electromagnetic response of the cavity is calculated by finite-difference time-domain(FDTD) simulations, and the optical force is characterized based on the Maxwell's stress tensor method. To be tweezers, this structure tends to trap quantum dots at the edges of its tips where light is significantly confined. To be a plasmonic cavity, its plasmonic resonant mode interacts strongly with the trapped quantum dots due to the enhanced electric field. Rabi splitting and anti-crossing phenomena are observed in the calculated scattering spectra, demonstrating that a strong-coupling regime has been achieved. The method present here provides a robust way to position a single quantum dot in a nanocavity for investigating cavity quantum electrodynamics.展开更多
This paper studies the size dependence of biexciton binding energy in single quantum dots (QDs) by using atomic force microscopy and micro-photoluminescence measurements. It finds that the biexciton binding energies...This paper studies the size dependence of biexciton binding energy in single quantum dots (QDs) by using atomic force microscopy and micro-photoluminescence measurements. It finds that the biexciton binding energies in the QDs show "binding" and "antibinding" properties which correspond to the large and small sizes of QDs, respectively. The experimental results can be well interpreted by the biexciton potential curve, calculated from the exciton molecular model and the Heitler London method.展开更多
The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules,quantum dots and plasmonic nanoparticles.Optimal co...The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules,quantum dots and plasmonic nanoparticles.Optimal control of the extremely short-lived coherences of these individual systems has so far remained elusive,yet its successful implementation would enable arbitrary external manipulation of otherwise inaccessible nanoscale dynamics.In ensemble measurements,such control is often achieved by resorting to a closed-loop optimization strategy,where the spectral phase of a broadband laser field is iteratively optimized.This scheme needs long measurement times and strong signals to converge to the optimal solution.This requirement is in conflict with the nature of single emitters whose signals are weak and unstable.Here we demonstrate an effective closed-loop optimization strategy capable of addressing single quantum dots at room temperature,using as feedback observable the two-photon photoluminescence induced by a phase-controlled broadband femtosecond laser.Crucial to the optimization loop is the use of a deterministic and robust-against-noise search algorithm converging to the theoretically predicted solution in a reduced amount of steps,even when operating at the few-photon level.Full optimization of the single dot luminescence is obtained within~100 trials,with a typical integration time of 100 ms per trial.These times are faster than the typical photobleaching times in single molecules at room temperature.Our results show the suitability of the novel approach to perform closed-loop optimizations on single molecules,thus extending the available experimental toolbox to the active control of nanoscale coherences.展开更多
The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains el...The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains elusive how these two phenomena are linked to each other.Unraveling the potential link between blinking and QCSE could facilitate the adoption of appropriate strategies that can simultaneously suppress both PL blinking and spectral diffusion.In this work,we investigated the blinking mechanism and QCSE of single CdSe/CdS/ZnS QDs in the presence of positive and negative surface charges using single-dot PL spectroscopy.We found that the negative surface charges can simultaneously suppress PL blinking and spectral diffusion of single QDs.On the other hand,the positive surface charges could change the blinking mechanisms of QDs from Auger-blinking to band-edge carrier(BC)-blinking.Two types of QCSE were observed,and a significant QCSE-induced spectral broadening of 5.25 nm was measured,which could be attributed to the hopping of surface charges between different surface-trap sites.Based on these findings,several theoretical models are proposed to explain various phenomena observed.展开更多
基金supported by the National Key Basic Research Program of China(Grant No.2013CB933304)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB01010200)the National Natural Science Foundation of China(Grant No.65015196)
文摘The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots(SQDs) to raise the growth repeatability.Here,through many growth tests on rotating substrates,we develop a proper In deposition amount(θ) for SQD growth,according to the measured critical θ for test QD nucleation(θ;).The proper ratio θ/θ;,with a large tolerance of the variation of the real substrate temperature(T;),is 0.964-0.971 at the edge and> 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer,and around 0.9709 but < 0.9714 in the center of a 1/4-piece N;wafer as shown in the evolution of QD size and density as θ/θ;varies.Bright SQDs with spectral lines at 905 nm-935 nm nucleate at the edge and correlate with individual 7 nm-8 nm-height QDs in atomic force microscopy,among dense 1 nm-5 nm-height small QDs with a strong spectral profile around 860 nm-880 nm.The higher T;in the center forms diluter,taller and uniform QDs,and very dilute SQDs for a proper θ/θ;:only one 7-nm-height SQD in25 μm;.On a 2-inch(1 inch = 2.54 cm) semi-insulating wafer,by using θ/θ;= 0.961,SQDs nucleate in a circle in 22%of the whole area.More SQDs will form in the broad high-T;region in the center by using a proper θ/θ;.
基金National Key R&D Program of China(2016YFA0301300)
文摘We report here a nanostructure that traps single quantum dots for studying strong cavity-emitter coupling. The nanostructure is designed with two elliptical holes in a thin silver patch and a slot that connects the holes. This structure has two functionalities:(1) tweezers for optical trapping;(2) a plasmonic resonant cavity for quantum electrodynamics. The electromagnetic response of the cavity is calculated by finite-difference time-domain(FDTD) simulations, and the optical force is characterized based on the Maxwell's stress tensor method. To be tweezers, this structure tends to trap quantum dots at the edges of its tips where light is significantly confined. To be a plasmonic cavity, its plasmonic resonant mode interacts strongly with the trapped quantum dots due to the enhanced electric field. Rabi splitting and anti-crossing phenomena are observed in the calculated scattering spectra, demonstrating that a strong-coupling regime has been achieved. The method present here provides a robust way to position a single quantum dot in a nanocavity for investigating cavity quantum electrodynamics.
基金Project supported by the National Natural Science Foundations of China (Grant Nos O69C041001 and 2007CB924904)
文摘This paper studies the size dependence of biexciton binding energy in single quantum dots (QDs) by using atomic force microscopy and micro-photoluminescence measurements. It finds that the biexciton binding energies in the QDs show "binding" and "antibinding" properties which correspond to the large and small sizes of QDs, respectively. The experimental results can be well interpreted by the biexciton potential curve, calculated from the exciton molecular model and the Heitler London method.
基金funded by the European Commission(ERC Adv.Grant 247330-NanoAntennas and ERC Adv.Grant 670949-LightNet)Spanish Severo Ochoa Programme for Centres of Excellence in R&D(SEV-2015-0522)+3 种基金Plan Nacional Project FIS2012-35527,co-funded by FEDER,the Catalan AGAUR(2014 SGR01540)Fundació CELLEX(Barcelona)support from Spanish Government MINECO-FPI grant and European Science Foundation under the PLASMON-BIONANOSENSE Exchange Grant programsupport from grants MICINN TEC2011-22422 and MINECO TEC2014-52642-C2-1-R.
文摘The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules,quantum dots and plasmonic nanoparticles.Optimal control of the extremely short-lived coherences of these individual systems has so far remained elusive,yet its successful implementation would enable arbitrary external manipulation of otherwise inaccessible nanoscale dynamics.In ensemble measurements,such control is often achieved by resorting to a closed-loop optimization strategy,where the spectral phase of a broadband laser field is iteratively optimized.This scheme needs long measurement times and strong signals to converge to the optimal solution.This requirement is in conflict with the nature of single emitters whose signals are weak and unstable.Here we demonstrate an effective closed-loop optimization strategy capable of addressing single quantum dots at room temperature,using as feedback observable the two-photon photoluminescence induced by a phase-controlled broadband femtosecond laser.Crucial to the optimization loop is the use of a deterministic and robust-against-noise search algorithm converging to the theoretically predicted solution in a reduced amount of steps,even when operating at the few-photon level.Full optimization of the single dot luminescence is obtained within~100 trials,with a typical integration time of 100 ms per trial.These times are faster than the typical photobleaching times in single molecules at room temperature.Our results show the suitability of the novel approach to perform closed-loop optimizations on single molecules,thus extending the available experimental toolbox to the active control of nanoscale coherences.
基金the National Key Research and Development Program of China(No.2017YFA0304203)the National Natural Science Foundation of China(Nos.62127817,62075120,62075122,61875109,91950109,and 62105193),NSFCSTINT(No.62011530133)+3 种基金PCSIRT(No.IRT_17R70)Natural Science Foundation of Shanxi Province(No.201901D111010(ZD))Research Project Supported by Shanxi Scholarship Council of China(No.HGKY2019002)PTIT,Shanxi“1331 Project”,and 111 project(No.D18001).
文摘The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains elusive how these two phenomena are linked to each other.Unraveling the potential link between blinking and QCSE could facilitate the adoption of appropriate strategies that can simultaneously suppress both PL blinking and spectral diffusion.In this work,we investigated the blinking mechanism and QCSE of single CdSe/CdS/ZnS QDs in the presence of positive and negative surface charges using single-dot PL spectroscopy.We found that the negative surface charges can simultaneously suppress PL blinking and spectral diffusion of single QDs.On the other hand,the positive surface charges could change the blinking mechanisms of QDs from Auger-blinking to band-edge carrier(BC)-blinking.Two types of QCSE were observed,and a significant QCSE-induced spectral broadening of 5.25 nm was measured,which could be attributed to the hopping of surface charges between different surface-trap sites.Based on these findings,several theoretical models are proposed to explain various phenomena observed.
基金the financial support from the National Natural Science Foundation of China(11774326)the National Key R&D Program of China(2017YFA0304301)+2 种基金Innovation Program for Quantum Science and Technology(2021ZD0300204)Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)Anhui Initiative in Quantum Information Technologies。