35 research outputs found
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 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
Contamination control for wafer container used within 300 mm manufacturing for power microelectronics
This paper gives an overview about all activities performed within a common project between industrial and academic partners to define clean room concepts for the first worldwide high volume semiconductor front end facility IFD for 300 mm power semiconductors. The investigation within this study is the base for the 300 mm container strategy resulting in new innovative manufacturing and automation concepts. © 2016 Trans Tech Publications, Switzerland
Tunnel junction engineering for optimized metallic single-electron transistor
The development of metallic single-electron transistor (SET) depends on the downscaling and the electrical properties of its tunnel junctions (TJs). These TJs should insure high-ON current, low-OFF current, and low capacitance. We propose an engineered TJ based on multidielectric stacking. A number of high-k and low-k materials were considered to optimize the TJ's characteristics. The optimized TJ is proven to increase the ION current and the ION/IOFF ratio in a double-gate SET. Using TiO2 plasma oxidation and Al2O3 atomic layer deposition, an SET proof of concept, with a double layer TJ, was fabricated and characterized