Energy-time entanglement from a resonantly driven quantum dot three-level system

Entanglement is a major resource in advanced quantum technology, where it can enable secure exchange of information over large distances. Energy-time entanglement is particularly attractive for its beneficial robustness in fiber-based quantum communication and can be demonstrated in the Franson interferometer. We report on Franson-type interference from a resonantly driven biexciton cascade under continuous wave excitation. Our measurements yield a maximum visibility of (73 $\pm$ 2)% surpassing the limit of violation of Bell's inequality (70.7%) by more than one standard deviation. Despite being unable to satisfy a loophole free violation, our work demonstrates promising results concerning future works on such a system. Furthermore, our systematical studies on the impact of driving strength indicate that dephasing mechanisms and deviations from the cascaded emission have major impact on the degree of the measured energy-time entanglement

Polarity determination in ZnSe nanowires by HAADF STEM

High angle annular dark field scanning transmission electron microscopy is used to analyze the polarity of ZnSe nanowires grown, by molecular beam epitaxy, on GaAs substrates. The experimental results are compared to simulated images in order to verify possible experimental artefacts. In this work we show that for this type of nano-objects, a residual tilt of the specimen below 15 mrad, away from the crystallographic zone axis does not impair the interpretation of the experimental images

Insertion of CdSe quantumdots in ZnSe nanowires : MBE growth and microstructure analysis

ZnSe nanowire growth has been successfully achieved on ZnSe (100) and (111)B buffer layers deposited on GaAs substrates. Cubic [100] oriented ZnSe nanowires or [0001] oriented hexagonal NWs are obtained on (100) substrates while [111] oriented cubic mixed with [0001] oriented hexagonal regions are obtained on (111)B substrates. Most of the NWs are perpendicular to the surface in the last case. CdSe quantum dots were successfully incorporated in the ZnSe NWs as demonstrated by transmission electron microscopy, energy filtered TEM and high angle annular dark field scanning TEM measurements

Dynamic vibronic coupling in InGaAs quantum dots

The electron-phonon coupling in self-assembled InGaAs quantum dots is relatively weak at low light intensities, which means that the zero-phonon line in emission is strong compared to the phonon sideband. However, the coupling to acoustic phonons can be dynamically enhanced in the presence of an intense optical pulse tuned within the phonon sideband. Recent experiments have shown that this dynamic vibronic coupling can enable population inversion to be achieved when pumping with a blue-shifted laser and for rapid de-excitation of an inverted state with red detuning. In this paper we confirm the incoherent nature of the phonon-assisted pumping process and explore the temperature dependence of the mechanism. We also show that a combination of blue- and red-shifted pulses can create and destroy an exciton within a timescale ∼ 20 ps determined by the pulse duration and ultimately limited by the phonon thermalisation time

Ultrafast single photon emitting quantum photonic structures based on a nano-obelisk

A key issue in a single photon source is fast and efficient generation of a single photon flux with high light extraction efficiency. Significant progress toward high-efficiency single photon sources has been demonstrated by semiconductor quantum dots, especially using narrow bandgap materials. Meanwhile, there are many obstacles, which restrict the use of wide bandgap semiconductor quantum dots as practical single photon sources in ultraviolet-visible region, despite offering free space communication and miniaturized quantum information circuits. Here we demonstrate a single InGaN quantum dot embedded in an obelisk-shaped GaN nanostructure. The nano-obelisk plays an important role in eliminating dislocations, increasing light extraction, and minimizing a built-in electric field. Based on the nano-obelisks, we observed nonconventional narrow quantum dot emission and positive biexciton binding energy, which are signatures of negligible built-in field in single InGaN quantum dots. This results in efficient and ultrafast single photon generation in the violet color region

Epitaxial growth of ZnSe and ZnSe/CdSe nanowires on ZnSe

International audienc

Correction to Ultrafast Room Temperature Single-Photon Source from Nanowire-Quantum Dots

International audienc