Tunable All-Optical Filtering and Buffering in a Coupled Quantum Dot-Planar Photonic Crystal Structure

We theoretically investigate controlled tunable all-optical filtering and buffering of optical pulses in a hybrid nano-photonic structure, where a single quantum dot （QD） embedded in a photonic crystal nanocavity is sidecoupled between a bare nanocavity and a photonic crystal waveguide. We demonstrate that there is a sharp low-loss transmission peak in the transmission spectrum under even low QD-nanocavity coupling strength and the input optical pulses can be delayed up to several hundred picoseconds within the dephasing time of the QD. The filtering regime can be shifted readily by manipulating the detuning between the QD excitonic transition frequency and resonant frequency of the nanocavity mode, which can be explored in future for on-chip all-optical logic and signal processing.     

微腔中单量子点的受激辐射行为

研究了微腔中单模光场与一个三能级量子点相互作用系统.利用系统主方程作数值模拟计算微腔中单量子点的净受激辐射率随量子点和腔模耦合强度的变化,同时研究激光能级间衰减率γ23对净受激辐射率的影响.发现净受激辐射率随泵浦强度增大而呈现较快趋于饱和的曲线,这些饱和曲线随着耦合强度的增加又较快地趋于一个极值.而激光能级间衰减率γ23的增大使该激光的净受激辐射率的曲线组表现出相反的规律.     

Double-state controllable optical switching through three tunnel-coupled quantum dots inside waveguide coupled photonic crystal microcavity

We study optical transmission properties of a combined system which is composed of a photonic crystal (PC) microcavity with low quality factor Q, a triple quantum dot (QD) embedded in cavity and two parallel waveguides. We demonstrate that low coupling strength (i.e., the weak coupling regime) between a cavity and a dot, by means of electron tunnel-induced coupling, can lead to a type of double-state controllable optical switching under the experimentally available parameter conditions.     

Theoretical study of photon emission from single quantum dot emitter coupled to surface plasmons

Motivated by the recent pioneering advances on nanoscale plasmonics and also nanophotonics technology based on the surface plasmons (SPs), in this work, we give a master equation model in the Lindblad form and investigate the quantum optical properties of single quantum dot (QD) emitter coupled to the SPs of a metallic nanowire. Our main results demonstrate the QD luminescence results of photon emission show three distinctive regimes depending on the distance between QD and metallic nanowire, which elucidates a crossover passing from being metallic dissipative for much smaller emitter-nanowire distances to surface plasmon (SP) emission for larger separations at the vicinity of plasmonic metallic nanowire. Besides, our results also indicate that, for both the resonant case and the detuning case, through measuring QD emitter luminescence spectra and second-order correlation functions, the information about the QD emitter coupling to the SPs of the dissipative metallic nanowire can be extracted. This theoretical study will serve as an introduction to understanding the nanoplasmonic imaging spectroscopy and pave a new way to realize the quantum information devices.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

Polarization Properties of Quantum-Dot-Based Single Photon Sources

Polarization properties of single photons emitted by optical pumping from a single quantum dot （ QD） are studied by using a four-level system model. The model is capable of explaining the polarization uncertainty observed in single photon emission experiments. It is found that the dependence of photon emission efficiency and polarization visibility on pump power are opposite in general cases. By employing QDs with small size and strong carrier confinement, the photon polarization visibility under high pump power can be improved. In addition, embedding a QD into a well designed microcavity is also found to be favourable, whereas the trade-off between high polarization visibility and multi-photon emission is noted.     

微腔中单量子点的激光输出特性研究

研究一个四能级量子点耦合到单模光学腔中的量子系统,利用系统的主方程作数值模拟计算微腔中单量子点的激光输出强度随非相干泵浦的变化关系.结果显示量子点在泵浦作用下激光的输出有一个阈值;且量子点和腔模耦合强度增强时,产生激光的阈值明显减小,输出激光的峰值却增大.当泵浦作用继续增强到一定程度,因激光能级间的相干性被过强的非相干泵浦所破坏,单量子点激光输出变为零----出现了淬灭现象.     

Isolated single quantum dot emitters in all-epitaxial microcavities

Data are presented on a fabrication approach that places an isolated single quantum dot at the center of a semiconductor microcavity. The microcavity is based on an all-epitaxial mesa-confined design that is mechanically robust and provides the thermal dissipation needed for a single photon source device technology. Microphotoluminescence is used to reveal single quantum dot emission with the essential optical properties of single quantum emitters.     

Coupling effects in a photonic crystal microcavity with embedded semiconductor quantum dot

The present work investigates the effects of relevant parameters of InAs/GaAs quantum dot and photonic crystal slab-based microcavity on the QD–cavity coupling characteristics, in detail. We employ variational approach to find exciton state in QD and to find cavity modes we use the open source GME code. Calculations have performed in linear regime where excitons behave as bosons which correspond to the limit of low excitation. The dynamics of the system are studied using the first order correlation function (G⁽¹⁾(t,τ)). We will show how G⁽¹⁾ varies with time in both strong and weak coupling regimes. Our results indicate that the achieving of strong coupling regime is affected by the size of the quantum dot and how to engineer the photonic crystal microcavity to maximize the ratio of quality factor and mode volume.     

Controllable four-wave mixing based on quantum dot-cavity coupling system

We theoretically study the four-wave mixing(FWM) response in a quantum dot-cavity coupling system, where a two-level quantum dot(QD) is placed in an optical cavity while the cavity mode is coupled to the nanomechanical resonator via radiation pressure. The influences of the QD-cavity coupling strength, the Rabi coupling strength of the QD, and the power of the pump light on the FWM intensity are mainly considered. The numerical results show that the FWM intensity in this hybrid system can be significantly enhanced by increasing the QD-cavity coupling strength. In addition, the FWM intensity can be effectively modulated by the Rabi coupling strength and the pump power. Furthermore, the effects of the cavity decay rate and the cavitypump detuning on the FWM signal are also explored. The obtained results may have potential applications in the fields of quantum optics and quantum information science.     

Efficient source of single photons: a single quantum dot in a micropost microcavity

We have demonstrated efficient production of triggered single photons by coupling a single semiconductor quantum dot to a three-dimensionally confined optical mode in a micropost microcavity. The efficiency of emitting single photons into a single-mode traveling wave is approximately 38%, which is nearly 2 orders of magnitude higher than for a quantum dot in bulk semiconductor material. At the same time, the probability of having more than one photon in a given pulse is reduced by a factor of 7 as compared to light with Poissonian photon statistics.     

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.     

Deterministic CNOT gate and entanglement swapping for photonic qubits using a quantum-dot spin in a double-sided optical microcavity

Abstract We propose a deterministic and scalable scheme to construct a two-qubit controlled-NOT (CNOT) gate and realize entanglement swapping between photonic qubits using a quantum-dot (QD) spin in a double-sided optical microcavity. The scheme is based on spin selective photon reflection from the cavity and can be achieved in a nondestructive and heralded way. We assess the feasibility of the scheme and show that the scheme can work in both the weak coupling and the strong coupling regimes. The scheme opens promising perspectives for long-distance photonic quantum communication and distributed quantum information processing.     

Strong exciton-photon coupling and exciton hybridization in a thermally evaporated polycrystalline film of an organic small molecule

We demonstrate strong exciton-photon coupling in an optical microcavity containing a thermally evaporated polycrystalline organic thin film. Microcavity polaritons result from coupling between the 0-0 excitonic transition of 3,4,7,8 napthalenetetracarboxylic dianhydride and a cavity photon. For thicker films, the 0-1 transition also couples to the cavity mode, as vibronic relaxation is overcome by the short Rabi period for strong coupling. To our knowledge, this is the first report of strong coupling between a cavity photon and multiple vibronic transitions in a single material, made possible by the pronounced vibronic absorption features characteristic of crystalline organic materials.     

Controlled waveguide coupling for photon emission from colloidal PbS quantum dot using tunable microcavity made of optical polymer and silicon

A tunable microcavity device composed of optical polymer and Si with a colloidal quantum dot (QD) is proposed as a single-photon source for planar optical circuit. Cavity size is controlled by electrostatic micromachine behavior with the air bridge structure to tune timing of photon injection into optical waveguide from QD. Three-dimensional positioning of a QD in the cavity structure is available using a nanohole on Si processed by scanning probe microscope lithography. We fabricated the prototype microcavity with PbS-QD-mixed polymenthyl methacrylate on a SOI (semiconductor-on-insulator) substrate to show the tunability of cavity size as the shift of emission peak wavelength of QD ensemble.     

Coherent photonic coupling of semiconductor quantum dots

We report a new type of coupling between quantum dot excitons mediated by the strong single-photon field in a high-finesse micropillar cavity. Coherent exciton coupling is observed for two dots with energy differences of the order of the exciton-photon coupling. The coherent coupling mode is characterized by an anticrossing with a particularly large line splitting of 250 microeV. Because of the different dispersion relations with temperature, the simultaneous photonic coupling of quantum dot excitons can be easily distinguished from cases of sequential strong coupling of two quantum dots.     

量子点单光子源的光纤耦合

半导体量子点在低温下产生谱线细锐的激子发光可制备单光子源.光纤耦合可避免低温共聚焦装置扫描定位和振动影响,是实现单光子源即插即用和组件化的关键技术.在耦合工艺上,基于微区定位标记发展出拉锥光纤与光子晶体腔或波导侧向耦合、大数值孔径锥形端面光纤与量子点样片垂直耦合等技术;然而,上述工艺需要多维度精密调节以避免柔软光纤的畸形弯曲实现对准和高效耦合.陶瓷插针或石英V槽封装的光纤无弯曲且具有大平滑端面,只要与单量子点样片对准贴合就可保证垂直收光, V槽封装的排式光纤还可通过盲对粘合避免扫描对准,耦合简单.本文在前期排式光纤粘合少对数分布Bragg反射镜(distributed Bragg reflector, DBR)微柱样片实现单光子输出基础上,经理论模拟采用多对数DBR腔提升样片垂直出光和光纤收光效率,使光纤输出单光子计数率大大提升.     

Dot-in-a-dot: electronic and photonic confinement in all three dimensions

We have studied the optical properties of three-dimensionally confined photon states in a spherical microcavity (the photonic dots) resonantly excited by photons emitted from semiconductor nanocrystals (the quantum dots). Glass and polymer microspheres with sizes of 2<R<10 are characterized by spatially and temporally resolved micro-photoluminescence. The role of nanocrystal position and orientation is analyzed experimentally and theoretically. The emission spectra of single, bulk and hollow microspheres impregnated with CdSe quantum dots and quantum rods are investigated and the modification of the quantum dot radiative lifetime by the three-dimensional photon confinement is discussed. PACS 78.66.Hf; 61.46.+w; 42.60.Da     

量子点腔非谐振耦合系统纯退相干的特性及应用

采用非相干泵浦、受激辐射和纯退相干的量子主方程研究了量子点腔耦合系统,得出腔与量子点发射光谱解析解.理论分析显示,在非谐振耦合系统中纯退相干能使腔发射谱产生明显的移位效应,从而可以解释“非谐振耦合腔有效发射”效应.为了进一步研究纯退相干在量子点腔耦合系统上的应用,引入了系统有效耦合率和单光子源效率,并通过比较有效耦合率与腔耗散定义出好腔与坏腔机制.选取两组依据实验数据作为参量,在共振与失谐时研究了纯退相干对系统有效耦合率和单光子源效率的影响.结果表明:纯退相干可提高失谐系统有效耦合率与单光子源效率,从而可能使坏腔转变为好腔|两组参量中有较大耦合效率一组在一定范围内满足好腔机制,其单光子源效率明显优于另一组.在非谐振耦合系统比较了好腔机制与坏腔机制的激光,好腔机制是实现单量子点激光的必要条件|由于非谐振耦合系统Fano因子无最大值出现,从而该系统可能无激光阈值.     

Single-mode spontaneous emission from a single quantum dot in a three-dimensional microcavity

The spontaneous emission from an isolated semiconductor quantum dot state has been coupled with high efficiency to a single, polarization-degenerate cavity mode. The InAs quantum dot is epitaxially formed and embedded in a planar epitaxial microcavity, which is processed into a post of submicron diameter. The single quantum dot spontaneous emission lifetime is reduced from the noncavity value of 1.3 ns to 280 ps, resulting in a single-mode spontaneous emission coupling efficiency of 78%.