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Recently, much research concerning the combination of nano-scale waveguides with nano-crystals and other nano-particles has been reported because of possible applications in the field of quantum information and communication. The most useful and convenient method to verify the nature of such systems is optical detection. However, due to the diffraction limit, optical identification of characteristics such as particle type, particle position, etc., is difficult or impossible. However, if such particles are placed on a waveguide, the coupling of scattered light to the waveguide-guided modes can reveal the information about the particles. Here we consider how illumination with light of arbitrary polarization can reveal the difference between isotropic and non-isotropic nano-particles placed on the surface of an optical nanofiber. Specifically, we measure the polarization response function of gold nano-rods (GNRs) on an optical nanofiber surface and show that it is qualitatively different to that for gold nano-spheres (GNSs). This experimental technique provides a simple new tool for the optical characterization of hybrid nano-optical devices.

Single-photon sources are essential tools for quantum information technology and testing the foundations of quantum theory. To date, single-photon sources which emit purely polarized single photons (e.g. horizontal polarization and vertical polarization) have been realized in various ways. On the other hand, single-photon sources which emit completely unpolarized single photons are also important for applications such as realizing hardware random number generators and testing the foundations of quantum theory such as the error-disturbance relation for mixed states [1, 2] which are quantum states of unpolarized polarization states. Here, we present a dynamically and statically unpolarized single-photon source using a single nitrogen-vacancy (NV) center in diamond. In particular, we demonstrate a new method for evaluation of dynamical unpolarization using the second order correlation function [3].

We report on the polarization dependence for hyper-Rayleigh scattering (HRS) in two-photon resonance with exciton states in ZnSe. The HRS signal is enhanced drastically when twice the incident photon energy is resonant with the excitation energy of the 2P excitons in ZnSe/GaAs thin films. The selection rules for the HRS in two-photon resonance with the 2P excitons are different from those for nonlinear susceptibility determined by crystal symmetry. Further, we report a study of the symmetries of the 2P excitonic wave function with linearly- and circularly-polarized incident beams. The heavy and light hole 2P excitons belong to different symmetries of the base functions.

We develop a theory of active dephasing control of qubit systems in array structures by using the multi-wave mixing technique. Assuming an acoustic phonon with a cutoff frequency ω c as the reservoir boson, we evaluate the state evolution of the qubit–reservoir system under irradiation of an optical pulse sequence. The effect of active dephasing control by the optical π pulses would be observed as diffracted echo signals in the phase-matching direction. The analysis for the case of weak pulse control is also presented.

We propose a novel scheme to generate polarization entanglement from spatially-correlated photon pairs. We experimentally realized a scheme by means of a spatial correlation effect in a spontaneous parametric down-conversion and a modified Michelson interferometer. The scheme we propose in this paper can be interpreted as a conversion process from spatial correlation to polarization entanglement., 4 pages, 4 figures

We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g-factors of electrons and light holes. The result encourages us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors., Comment: 4 pages. Submitted to Physical Review Letters

The authors demonstrate polarization transfer from a photon to an electron spin intermediated by a light-hole exciton in a GaAs∕AlGaAs quantum well, which has an engineered electron g factor of less than 0.01 for an in-plane magnetic field. Negative spin polarization was clearly observed at the selective excitation of the light-hole exciton from two-color time-resolved Kerr rotation. This demonstration is a necessary step towards demonstrating coherence transfer from a photon to an electron spin, which is necessary for building a quantum repeater used for long distance quantum communications.

Dynamics of photoinduced magnetization rotation was studied in ferromagnetic p-(Ga,Mn)As by carefully comparing the temporal profile of the photoinduced polar Kerr rotation with that of the photoinduced reflectivity change. Rotation of ferromagnetically coupled Mn spins is induced by photogenerated hole spins within the excitation pulse width of a 100 fs, whereas relaxation takes place in tens of picosecond as a result of strong damping. Observed results suggest that hole and Mn spins rotate and relax together upon optical excitation. This would be a different type of excitation (coupled hole-Mn spin complex) appearing in the hole-mediated ferromagnetic system.