Hirotaka Sasakura

Position controlled nanowires for infrared single photon emission

We report the experimental demonstration of single-photon and cascaded photon pair emission in the infrared, originating from a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires is fabricated by epitaxial growth on an electron-beam patterned substrate. Photoluminescence spectra taken on single quantum dots show narrow emission lines. Superconducting single photon detectors, which have a higher sensitivity than avalanche photodiodes in the infrared, enable us to measure auto and cross correlations. Clear antibunching is observed [g(2)(0) = 0.12] and we show a biexciton–exciton cascade, which can be used to create entangled photon pairs.

Temperature dependent carrier dynamics in telecommunication band InAs quantum dots and dashes grown on InP substrates

InAs quantum dots (QDs) grown on InP substrates can be used as light emitters in the telecommunication bands. In this paper, we present optical characterization of high-density circular quantum dots (QDots) grown on InP(311)B substrates and elongated dots (QDashes) grown on InP(001) substrates. We study the charge carrier transfer and luminescence thermal quenching mechanisms of the QDots and QDashes by investigating the temperature dependence of their time-integrated and time-resolved photoluminescence properties. This results in two different contributions of the thermal activation energies. The larger activation energies are attributed to the carrier escape to the barrier layer and the wetting layer (WL) from QDots and QDashes, respectively. The smaller activation energies are found to be originated from inter-dot/dash carrier transfer via coupled excited states. The variation of the average oscillator strength associated with the carrier re-distribution is discussed. The relation of the two activation...

Optical anisotropy and photoluminescence polarization in single InAlAs quantum dots

We have investigated the optical anisotropy in individual self-assembled quantum dots. The linear polarization analysis of the positive trion photoluminescence reveals the effect of the strain-induced valence band mixing since the positive trion has the spin-paired holes and therefore exchange interaction has no influence. Meanwhile, the neutral exciton indicates the complex polarization states due to both the in-plain asymmetries of the dot shape and the strain distributions. The experimental and theoretical polarization analysis has been performed for tens of InAlAs quantum dots and the correlation between the important parameters was investigated.

Polarization-dependent shift in excitonic Zeeman splitting of self-assembled In0.75Al0.25As /Al0.3Ga0.7As quantum dots

We report optical spectroscopic results of a single self-assembled

Photon-spin qubit-conversion based on Overhauser shift of Zeeman energies in quantum dots

{\mathrm{In}}_{0.75}{\mathrm{Al}}_{0.25}\mathrm{As}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}

Enhanced Photon Generation in a Nb/n-InGaAs/p-InP Superconductor/Semiconductor-Diode Light Emitting Device

quantum dot. The polarization-dependent shift of the Zeeman splitting in a single InAlAs quantum dot (QD) has been observed. The induced Overhauser field is estimated to be

Spin Depolarization via Tunneling Effects in Asymmetric Double Quantum Dot Structure

\ensuremath{\sim}0.16\phantom{\rule{0.3em}{0ex}}\mathrm{T}

Photon Antibunching Observed from an InAlAs Single Quantum Dot

in this InAlAs QD and the magnitude is shown to be controllable by the degree of circular polarization of excitation light.

Decoherence of exciton complexes in single InAlAs quantum dots measured by Fourier spectroscopy

We propose a method to realize the conversion of photon qubit and spin qubit using the effective magnetic field created by the nuclear polarization known as Overhauser field. We discuss the preliminary experiment on an InAlAs∕AlGaAs self-assembled quantum dot and also discuss the effects of electron-hole interaction on the conversion.

Long spin relaxation in self-assembled InAlAs quantum dots observed by heterodyne four-wave mixing

Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan 2CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan 3Graduate School of Information Science Technology, Hokkaido University, Sapporo 060-0814, Japan 4Central Research Laboratory, Hamamatsu Photonics, Hamamatsu 434-8601, Japan 5NTT Basic Research Laboratory, Atsugi 243-0198, Japan 6Japan Science and Technology Agency, Kawaguchi 332-0012, Japan Department of Applied Physics, Tokyo University of Science, Tokyo 162-8601, Japan 8Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan (Dated: October 27, 2009)