The authors report a “plug and play” source of single photons, with full integration to a single-mode optical fiber. One end of the fiber is attached to the top of an InGaAs∕GaAs quantum dot wafer. The other end is connected via a wavelength-division multiplexing system to two separate fibers: one for carrying excitation light and the other for emitted light. A Hanbury-Brown and Twiss [Nature (London) 77, 27 (1956)] measurement was performed on the emission from single excitons recombining in the quantum dots. A second-order correlation function at zero time delay of approximately 0.01 indicates a nearly ideal source of single photons. The maximum variation of peak position over 24days is less than 0.1nm.

Ultrafast initialization enables fault-tolerant processing of quantum information while QND read-out enables scalable quantum computation. By spatially assembling photon resonators and wave-guides around an n-doped nanodot and by temporally designing optical pump pulses, an efficient quantum pathway can be established from an electron spin to a charged exciton to a cavity photon and finally to a flying photon in the waveguide. Such control of vacuum-nanodot coupling can be exploited for ultrafast initialization and QND readout of the spin, which are particularly compatible with the optically driven spin quantum computers. Vacuum electromagnetic (EM) fluctuation plays an important role in quantum dynamics of nuclei [1], atoms [2], electrons [3], and solid-state quantum structures [4]. Recent advances in optical micro-structures, such as micro-spheres [5, 6], micro-rings [7, 8], micro-pillars [9], and engineered defects in photonic crystals [10], offer an opportunity of modifying the vacuum EM environment of various systems with a great extent of controllability. Novel ideas have been demonstrated such as engineering the Casimir force in microelectromechanical systems [11] and assembling semiconductor quantum dots inside photon resonators for efficient single photon sources [9]. At the same time, modern technology in ultrafast optics allows almost arbitrary design of laser pulses for coherent control [12]. Optical control of excitons in quantum dots has become one of the methods for building solid-state processors of quantum information [13, 14, 15]. Possessing ultra-long coherence time, electron spins in quantum dots are among the top candidates for quantum computing [16, 17]. Recent advances in quantum optics experiments have encouraged the proposals of optical manipulation of spins on the picosecond scale. In particular, Raman process [15] and optical RKKY interaction [14] mediated by charged excitons have been proposed for single-spin and two-spin operations, respectively , which constitute a set of gates for universal quantum computing. To make quantum computing complete , reading (measurement) and writing (initialization) of the qubits are two basic steps. Because the direct coupling between spins and their EM environment is extremely weak (which favors the long coherence time), spin readout has been a formidable task under investigation [18, 19, 20, 21, 22, 23, 24]. In most existing schemes [18, 19, 20, 21, 22], the spin state is first mapped into an orbit state which is then detected by electric sensors. These readout schemes, limited by the clock speed of the electric measurement and/or requiring local magnetic control, is not ideally suited for optically operated spin quantum computers. The ultrafast initialization of an individual qubit is essential in quantum error correction and fault-tolerant quantum computing [25], for the error (entropy) has to be erased as it is generated during processing [26]. Much less attention has been paid to the speed of initialization [22] than its importance would suggest...

Computer simulation and modeling of coupled heat and moisture transfer are becoming increasingly significant for accurate calculations of heat and moisture transfer. However, to solve their equations, the true component, l, of apparent thermal conductivity, l app , as a function of temperature, moisture content, and material structure is required. An approach to the development of a comprehensive database for l is discussed. Its key feature is demonstrated by the development of a theoretical model for l and l app of two common building insulation materials -expanded polystyrene insulation and highly porous calcium silicate -for a wide range of temperature and moisture conditions.