Microring-Assisted Coupling Between Dissimilar Waveguides

The use of microring resonators to assist in the evanescent field coupling between dissimilar waveguides is proposed and analyzed. Theoretical analysis based on the coupled mode theory and nu-merical example show that complete cross power transfers can be obtained near the microring resonances. Applications of the device include power dividers, low-power thermo-optic or electro-optic switches, and modulators.     

Laser cooling and real-time measurement of the nuclear spin environment of a solid-state qubit

Control over quantum dynamics of open systems is one of the central challenges in quantum science and engineering. Coherent optical techniques, such as coherent population trapping involving dark resonances, are widely used to control quantum states of isolated atoms and ions. In conjunction with spontaneous emission, they allow for laser cooling of atomic motion, preparation and manipulation of atomic states, and rapid quantum optical measurements that are essential for applications in metrology. Here we show that these techniques can be applied to monitor and control individual atom-like impurities, and their local environment, in the solid state. Using all-optical manipulation of the electronic spin of an individual nitrogen-vacancy colour centre in diamond, we demonstrate optical cooling, real-time measurement and conditional preparation of its nuclear spin environment by post-selection. These methods offer potential applications ranging from all-optical nanomagnetometry to quantum feedback control of solid-state qubits, and may lead to new approaches for quantum information storage and processing.     

彩色多普勒超声在腹壁下动脉穿支选择中的应用

验证彩色多普勒超声对腹壁下动脉穿支血管术前探查的有效性,寻找腹壁下动脉穿支术前优势穿支的选择标准。利用彩色多普勒超声探查腹壁下动脉穿支皮瓣行乳房再造患者52例,重点记录穿支血管穿腹直肌前鞘点的体表投影、口径、血流信息,并通过分析比较以上信息,选择优势穿支。结果52例患者腹壁下动脉穿支穿腹直肌前鞘点于超声下均可显示,平均每侧下腹部3支,距脐平均(5.7±2.09)cm,其中条件适用于显微外科的穿支平均口径(0.95±0.32)cm,血流峰速平均约16.4 cm/s,阻力指数平均0.7。术中优势穿支采用率92.31%。说明高频彩色多普勒超声适用于腹壁下动脉穿支皮瓣术前血管探查,可精确指导穿支的术前选择,辅助手术方案制定以及皮瓣设计。     

Electromagnetically induced transparency with tunable single-photon pulses

Techniques to facilitate controlled interactions between single photons and atoms are now being actively explored. These techniques are important for the practical realization of quantum networks, in which multiple memory nodes that utilize atoms for generation, storage and processing of quantum states are connected by single-photon transmission in optical fibres. One promising avenue for the realization of quantum networks involves the manipulation of quantum pulses of light in optically dense atomic ensembles using electromagnetically induced transparency (EIT, refs 8, 9). EIT is a coherent control technique that is widely used for controlling the propagation of classical, multi-photon light pulses in applications such as efficient nonlinear optics. Here we demonstrate the use of EIT for the controllable generation, transmission and storage of single photons with tunable frequency, timing and bandwidth. We study the interaction of single photons produced in a 'source' ensemble of 87Rb atoms at room temperature with another 'target' ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval.     

Long-distance quantum communication with atomic ensembles and linear optics.

Quantum communication holds promise for absolutely secure transmission of secret messages and the faithful transfer of unknown quantum states. Photonic channels appear to be very attractive for the physical implementation of quantum communication. However, owing to losses and decoherence in the channel, the communication fidelity decreases exponentially with the channel length. Here we describe a scheme that allows the implementation of robust quantum communication over long lossy channels. The scheme involves laser manipulation of atomic ensembles, beam splitters, and single-photon detectors with moderate efficiencies, and is therefore compatible with current experimental technology. We show that the communication efficiency scales polynomially with the channel length, and hence the scheme should be operable over very long distances.     

Quantum nonlinear optics with single photons enabled by strongly interacting atoms

The realization of strong nonlinear interactions between individual light quanta (photons) is a long-standing goal in optical science and engineering, being of both fundamental and technological significance. In conventional optical materials, the nonlinearity at light powers corresponding to single photons is negligibly weak. Here we demonstrate a medium that is nonlinear at the level of individual quanta, exhibiting strong absorption of photon pairs while remaining transparent to single photons. The quantum nonlinearity is obtained by coherently coupling slowly propagating photons to strongly interacting atomic Rydberg states in a cold, dense atomic gas. Our approach paves the way for quantum-by-quantum control of light fields, including single-photon switching, all-optical deterministic quantum logic and the realization of strongly correlated many-body states of light.     

Generation of single optical plasmons in metallic nanowires coupled to quantum dots

Control over the interaction between single photons and individual optical emitters is an outstanding problem in quantum science and engineering. It is of interest for ultimate control over light quanta, as well as for potential applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits. Recently, substantial advances have been made towards these goals, based on modifying photon fields around an emitter using high-finesse optical cavities. Here we demonstrate a cavity-free, broadband approach for engineering photon-emitter interactions via subwavelength confinement of optical fields near metallic nanostructures. When a single CdSe quantum dot is optically excited in close proximity to a silver nanowire, emission from the quantum dot couples directly to guided surface plasmons in the nanowire, causing the wire's ends to light up. Non-classical photon correlations between the emission from the quantum dot and the ends of the nanowire demonstrate that the latter stems from the generation of single, quantized plasmons. Results from a large number of devices show that efficient coupling is accompanied by more than 2.5-fold enhancement of the quantum dot spontaneous emission, in good agreement with theoretical predictions.     

Nanoscale magnetic sensing with an individual electronic spin in diamond

Detection of weak magnetic fields with nanoscale spatial resolution is an outstanding problem in the biological and physical sciences. For example, at a distance of 10 nm, the spin of a single electron produces a magnetic field of about 1 muT, and the corresponding field from a single proton is a few nanoteslas. A sensor able to detect such magnetic fields with nanometre spatial resolution would enable powerful applications, ranging from the detection of magnetic resonance signals from individual electron or nuclear spins in complex biological molecules to readout of classical or quantum bits of information encoded in an electron or nuclear spin memory. Here we experimentally demonstrate an approach to such nanoscale magnetic sensing, using coherent manipulation of an individual electronic spin qubit associated with a nitrogen-vacancy impurity in diamond at room temperature. Using an ultra-pure diamond sample, we achieve detection of 3 nT magnetic fields at kilohertz frequencies after 100 s of averaging. In addition, we demonstrate a sensitivity of 0.5 muT Hz(-1/2) for a diamond nanocrystal with a diameter of 30 nm.     

Effective Approach to Elevate the Intelligence of Management Decision System

Based on the sticking point of the low intelligence of the existing management decision system, this paper puts forward the idea of enriching and refining the knowledge of the system and endowing it with the ability to learn by means of adopting three types of heterogeneous knowledge representation and knowledge management measures. At length, this paper outlines the basic framework of an intelligence system for the sake of management decision problem.