Electrically Driven InAs Quantum-Dot Single-Photon Sources

Electrically driven single photon source based on single InAs quantum dot （QDs） is demonstrated. The device contains InAs QDs within a planar cavity formed between a bottom AlCaAs/CaAs distributed Bragg reflector （DBR） and a surface CaAs-air interface. The device is characterized by I-V curve and electroluminescence, and a single sharp exciton emission line at 966nm is observed. Hanbury Brown and Twiss （HBT） correlation measurements demonstrate single photon emission with suppression of multiphoton emission to below 45% at 80 K     

光纤光栅外腔半导体激光器的高频调制特性

报道了光纤光栅外腔激光器瞬态特性的理论分析,引入了一个适用于外腔情况的等效光子寿命,模拟计算表明,要获得高于2．5GHz的调制速率,光纤光栅外腔的长度必须短于4cm范围,对所研制的光纤光栅外腔激光器进行了高频调制测量,得到了在1GHz下的单模激光输出,边模抑制比在40dB以上,3dB动态线宽为0．1nm左右,20dB动态线宽为0．3nm。     

半导体自组织量子点量子发光机理与器件

介绍了自组织量子点单光子发光机理及器件研究进展.主要内容包括：半导体液滴自催化外延GaAs纳米线中InAs量子点和GaAs量子点的单光子发光效应、自组织InAs/GaAs量子点与分布布拉格平面微腔耦合结构的单光子发光效应和器件制备,单量子点发光的共振荧光测量方法、量子点单光子参量下转换实现的纠缠光子发射、单光子的量子存储效应以及量子点单光子发光的光纤耦合输出芯片制备等.     

半导体垂直腔面发射激光器的微腔效应

应用腔量子电动力学和半导体物理学讨论了半导体垂直腔面发射激光器的微腔效应,得到了实际腔结构和注入载流子下的半导体生趣腔面发射激光器的自发发射谱,计算结果表明,半导体分布布拉格反射垂直腔激光器的单方向自发发射可以境强约２００倍。     

Pump geometry for resonant and quasi-resonant optical excitation of microcavity lasers

A simple new pump geometry for optical excitation of microcavities and vertical-cavity surface-emitting lasers is presented. The technique circumvents the high reflectivity of the cavity stop band by excitation through the substrate at a large angle of incidence. Under these conditions, the reflectivity of the bottom Bragg reflector is small, and optical pumping at any desired photon energy becomes possible. Experimental results for optical excitation with this new geometry are compared with resonant optical pumping through the cavity mode.     

Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal

We observe large spontaneous emission rate modification of individual InAs quantum dots (QDs) in a 2D photonic crystal with a modified, high-Q single-defect cavity. Compared to QDs in a bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase of up to a factor of 8. In contrast, off-resonant QDs indicate up to fivefold rate quenching as the local density of optical states is diminished in the photonic crystal. In both cases, we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with a pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using finite difference time domain simulations and find good agreement with experiment.     

Intracavity weak nonlinear phase shifts with single photon driving

We investigate a doubly resonant optical cavity containing a Kerr nonlinear medium that couples two modes by a cross phase modulation. One of these modes is driven by a single photon pulsed field, and the other mode is driven by a coherent state. We find an intrinsic phase noise mechanism for the cross phase shift on the coherent beam which can be attributed to the random emission times of single photons from the cavity. An application to a weak nonlinearity phase gate is discussed.     

Controlled generation of single photons from a strongly coupled atom-cavity system

We propose a new method for the generation of single photons. Our scheme will lead to the emission of one photon into a single mode of the radiation field in response to a trigger event. This photon is emitted from an atom strongly coupled to a high-finesse optical cavity, and the trigger is a classical light pulse. The device combines cavity-QED with an adiabatic transfer technique. We simulate this process numerically and show that it is possible to control the temporal behaviour of the photon emission probability by the shape and the detuning of the trigger pulse. An extension of the scheme with a reloading mechanism will allow one to emit a bit-stream of photons at a given rate. Received: 7 July 1999 / Revised version: 3 September 1999 / Published online: 20 October 1999     

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.     

Photon bunching and anti-bunching with two dipole-coupled atoms in an optical cavity

We investigate the effect of the dipole–dipole interaction(DDI) on the photon statistics with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission. By means of the quantum trajectory analysis and the second-order correlation functions, we show that the photon statistics of the cavity transmission can be flexibly modulated by the DDI while the incoming coherent laser selectively excites the atom–cavity system's nonlinear Jaynes–Cummings ladder of excited states. Finally, we find that the effect of the cooperatively atomic emission can also be revealed by the numerical simulations and can be explained with a simplified picture. The DDI induced nonlinearity gives rise to highly nonclassical photon emission from the cavity that is significant for quantum information processing and quantum communication.     

Optical gain by simultaneous photon and phonon confinement in indirect bandgap semiconductor acousto-optical cavities

Optical gain that could ultimately lead to light emission from silicon is a goal that has been pursued for a long time by the scientific community. The reason is that a silicon laser would allow for the development of low-cost, high-volume monolithic photonic integrated circuits created using conventional CMOS technologies. However, the silicon indirect bandgap—requiring the participation of a proper phonon in the process of light emission—is a roadblock that has not been overcome so far. A high-Q optical cavity allowing a very high density of states at the desired frequencies has been proposed as a possible way to get optical gain. However, recent theoretical studies have shown that the free-carrier absorption is much higher than the optical gain at ambient temperature in an indirect bandgap semiconductor, even if a high-Q optical cavity is formed. In this work, we consider a particular case in which the semiconductor material is engineered to form an acousto-optical cavity where the photon and phonon modes involved in the emission process are simultaneously confined. The acousto-optical cavity confinement effect on the light emission properties is characterized by a compound Purcell factor which includes both the optical as well as the acoustic Purcell factor (APF). A theoretical expression for the APF is also introduced. Our theoretical results suggest that creating an acousto-optical cavity the optical gain can overcome the photon loss due to free carriers as a consequence of the localization of phonons even at room temperature, paving the way towards the pursued silicon laser.     

Asymmetric coherent photon tunneling filter in an optical waveguide structure

Based on the well-known electron coherent tunneling phenomenon, by simulation, a photonic tunneling filter fabricated in an optical waveguide is proposed. The Bragg grating structure is applied as the photonic barrier. Two photonic barriers confine a coherent resonance cavity or photon-quantum-well. We report an asymmetric-barrier structure with opposite phase. In this configuration, the central tunneling wavelength is exactly the same as the Bragg wavelength of the grating, independent of the photon-quantum-well dimension. The photon-quantum-well length can be adjusted to make the tunneling peak interval fall to a desired spacing. The photon barrier length is responsible for the filter bandwidth. As an application, an asymmetric grating photon tunneling filter with International Telecommunication Union grid is demonstrated.     

Atom detection and photon production in a scalable, open, optical microcavity

A microfabricated Fabry-Perot optical resonator has been used for atom detection and photon production with less than 1 atom on average in the cavity mode. Our cavity design combines the intrinsic scalability of microfabrication processes with direct coupling of the cavity field to single-mode optical waveguides or fibers. The presence of the atom is seen through changes in both the intensity and the noise characteristics of probe light reflected from the cavity input mirror. An excitation laser passing transversely through the cavity triggers photon emission into the cavity mode and hence into the single-mode fiber. These are first steps toward building an optical microcavity network on an atom chip for applications in quantum information processing.     

Exciton-photon interaction in low-dimensional semiconductor microcavities

The structure of the photon states and dispersion of cavity polaritons in semiconductor microcavities with two-dimensional optical confinement (photon wires), fabricated from planar Bragg structures with a quantum well in the active layer, are investigated by measuring the angular dependence of the photoluminescence spectra. The size quantization of light due to the wavelength-commensurate lateral dimension of the cavity causes additional photon modes to appear. The dispersion of polaritons in photon wires is found to agree qualitatively with the prediction for wires having an ideal quantum well, for which the spectrum is formed by pairwise interaction between exciton and photon modes of like spatial symmetry. The weak influence of the exciton symmetry-breaking random potential in the quantum well indicates a mechanism of polariton production through light-induced collective exciton states. This phenomenon is possible because the light wavelength is large in comparison with the exciton radius and the dephasing time of the collective exciton state is long. Zh. éksp. Teor. Fiz. 114, 1329–1345 (October 1998)     

Coupled-resonator optical waveguides doped with nanocrystals

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual cavity modes into coherently coupled waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. To demonstrate the formation of multisphere photon states, we use a bent linear array of microresonators and probe the properties of the cavity photon field by the spatially and spectrally resolved measurement of the nanocrystal emission. Photon mode coupling is evidenced by the observed mode splitting and emission intensity distributions along the CROW structure.     

镶嵌于多孔硅微腔中8-羟基喹啉铝的窄峰发射

利用浸渍法将8羟基喹啉铝(Alq₃)镶嵌到多孔硅微腔中,制备了多孔硅微腔—Alq₃镶嵌膜,研究了多孔硅微腔对镶嵌其中的Alq₃自发发射的微腔效应,观察到了光谱窄化、发光强度增强等现象。镶嵌于多孔硅微腔中的Alq₃荧光光谱的半峰全宽只有15nm,而非微腔样品,即镶嵌于普通的单层多孔硅中Alq₃荧光谱半峰全宽在85nm以上。并且有微腔时Alq₃发光强度比没有微腔时Alq₃发光强度增强一个数量级。随机改变微腔中Bragg反射镜高折射率层的几何厚度可使高反射区展宽,从而更加有效地抑制了多孔硅本身的发光模,使发光色度更纯,但由于峰值透射率减小,导致共振峰强度有所减小。多孔硅微腔有机镶嵌膜有可能成为进一步发展Alq₃在电致发光器件方面应用的一条新途径。     

原子系综中光学腔增强的Duan-Lukin-Cirac-Zoller写过程激发实验

原子系综中的Duan-Lukin-Cirac-Zoller(DLCZ)过程是产生光与原子(量子界面)量子关联和纠缠的重要手段.当一束写光与原子发生作用时,将会产生斯托克斯(Stokes)光子的自发拉曼散射,并同时产生一个自旋波(spin-wave)存储在原子系综中,上述过程即为DLCZ量子记忆产生过程.这一过程被广泛地研究.本文将87Rb原子系综放入驻波腔,并使Stokes光子与光学腔共振,我们观察到有腔且锁定的情况下Stokes光子产生概率比无腔时增大了8.7倍.在此条件下研究了Stokes光子产生概率和写光功率的关系,Stokes光子产生概率随写光功率线性增大.     

Enission spectra Of aΞ-type three-1evel atom in a Kerr medium

We investigate the emission spectra of a Ξ-type three-level atom interacting with a single-mode optical field in an ideal cavity filled with a Kerr medium and discuss the structure of emission spectrum when the optical field is initially in a pure number state and a coherent state, respectively. It is shown that the structure of emission spectrum depends not only on the photon number distribution, but also on the strength of incident field and the coupling of Kerr medium to the field.     

Vacuum-stimulated raman scattering based on adiabatic passage in a high-finesse optical cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counterintuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a subnatural linewidth. The results are in excellent agreement with numerical simulations.     

One-Step Implementation of Mulitqubit Quantum Phase Gate in a Cavity QED System

An alternative protocol is proposed to implement three-qubit phase gate between photon and atoms in a high-Q bimodel optical cavity. The idea can be extended to directly implement N-qubit phase gate, and the gating time that is required to implement the protocol does not rise with increasing number of qubits. The influence of cavity decay and atomic spontaneous emission on the gate fidelity is also discussed.