We report on the fabrication by Au-assisted molecular beam epitaxy of InP nanowires with embedded InAsP insertions. The growth temperature affects the nucleation on the nanowire lateral surface. It is therefore possible to grow the wires in two steps: to fabricate an axial heterostructure (at 420 degrees C), and then cover it by a shell (at 390 degrees C). The InAsP alloy composition could be varied between InAs0.35P0.65 and InAs0.5P0.5 by changing the As to P flux ratio. When a shell is present, the InAsP segments show strong room-temperature photoluminescence with a peak wavelength tunable from 1.2 to 1.55 mum by adjusting the As content. If the axial heterostructure has no shell, luminescence intensity is drastically reduced. Low-temperature microphotoluminescence performed on isolated single wires shows narrow peaks with a line width as small as 120 microeV.

We have fabricated superconducting nanowire single photon detectors made of NbTiN on a silicon substrate. This type of material reduces the dark count rate by a factor of 10 compared to identical NbN detectors, enabling single photon detection with unprecedented signal to noise ratio: we report a noise equivalent power of 10−19 W Hz−1/2 at 4.2 K. The compatibility of our superconducting device with silicon enables its integration with complex structures.

We report on a magnetophotoluminescence study of single self-assembled semiconductor nanorings which are fabricated by molecular-beam epitaxy combined with AsBr 3 in situ etching. Oscillations in the neutral exciton radiative recombination energy and in the emission intensity are observed under an applied magnetic field. Further, we control the period of the oscillations with a gate potential that modifies the exciton confinement. We infer from the experimental results, combined with calculations, that the exciton Aharonov-Bohm effect may account for the observed effects.

We report exciton spin memory in a single InAs(0.25)P(0.75) quantum dot embedded in an InP nanowire. By synthesizing clean quantum dots with linewidths as narrow as about 30 microeV, we are able to resolve individual spin states at magnetic fields on the order of 1 T. We can prepare a given spin state by tuning excitation polarization or excitation energy. These experiments demonstrate the potential of this system to form a quantum interface between photons and electrons.

Superconducting single photon detectors are usually fabricated in such a way that a polarization dependence of the quantum efficiency is inevitable. Their meandering nanowire leads to a preferential polarization absorption, this is undesired in experiments where the polarization degree of freedom is used. We have designed two new geometries for which the polarization dependence is minimized: a detector with two meander-type parts oriented perpendicular with respect to each other and a spiraling detector. Focusing on individual parts of the detectors shows polarization dependent quantum efficiency. When the detectors are illuminated uniformly, the maximum polarization dependent quantum efficiency cannot be achieved, however, the polarization dependence of the quantum efficiency is minimized.

We perform polarization-resolved magneto-optical measurements on single InAsP quantum dots embedded in an InP nanowire. In order to determine all elements of the electron and hole g-factor tensors, we measure in magnetic field with different orientations. The results of these measurements are in good agreement with a model based on exchange terms and Zeeman interaction. In our experiment, polarization analysis delivers a powerful tool that not only significantly increases the precision of the measurements, but also enables us to probe the exciton spin state evolution in magnetic fields. We propose a disentangling scheme of heavy-hole exciton spins enabling a measurement of the electron spin T2 time.

We study the absorption and emission polarization of single semiconductor quantum dots in semiconductor nanowires. We show that the polarization of light absorbed or emitted by a nanowire quantum dot strongly depends on the orientation of the nanowire with respect to the directions along which light is incident or emitted. Light is preferentially linearly polarized when directed perpendicular to the nanowire elongation. In contrast, the degree of linear polarization is low for light directed along the nanowire. This result is vital for photonic applications based on intrinsic properties of quantum dots, such as generation of entangled photons. As an example, we demonstrate optical access to the spin states of a single nanowire quantum dot. [7,8,9,10,11] brings additional unique features such as natural alignment of vertically stacked QDs [12] and an inherent one-dimensional channel for charge carriers. Furthermore, the unprecedented material and design freedom makes them very attractive for novel opto-electronic devices [13,14,15,16,17,18] and quantum information science in general [19,20,21,22]. However, access to intrinsic spin and polarization properties of a QD in a NW has never been demonstrated, most likely due to an insufficient quality of the NW QDs. Moreover, the NW geometry strongly affects the polarization of photons emitted or absorbed by a NW QD, and thus becomes the main obstacle for applications based on intrinsic spin or polarization properties of QDs such as an electron spin memory [23] or generation of entangled photons [3]. Indeed, it has been shown that luminescence of pure NWs is highly linearly polarized and the polarization direction is parallel to the NW elongation [13,17,24].In this Letter we demonstrate that by directing light along the NW elongation we can access intrinsic spin and polarization properties of a QD in a NW. We introduce a theoretical model which intuitively explains our experimental findings and shows how polarization is affected by various parameters such as NW diameter, dielectric constant of the surroundings and photon wavelength. As an example, we demonstrate access to the spin properties of a Zeeman split exciton in a QD by measuring the right-and left-hand circular photon polarization.For our experiments we used single InAs 0.25 P 0.75 QDs embedded in InP NWs, grown by means of metal-organic vapor-phase epitaxy [25,26,27,28]. Colloidal gold particles of 20 nm diameter were deposited on a (111)B InP substrate as catalysts for vertical NW growth. The diameter of the NW and the QD was controlled by the gold particle size, while the NW density was set by the gold particle density on the substrate. The QD height and NW length were determined by growth time [8]. By controlling diameter, height, and As concentration one can tune the QD emission in the wide range of 900 nm to 1.5 µm [9]. Under appropriate growth conditions we were able to grow a sample with low density of NWs with a single QD that emits around 950 nm. In Fig. 1a) we show a scanning electron microscope (SE...

Kouwen, Van