6 research outputs found
MBE Growth of Al/InAs and Nb/InAs Superconducting Hybrid Nanowire Structures
We report on \textit{in situ} growth of crystalline Al and Nb shells on InAs
nanowires. The nanowires are grown on Si(111) substrates by molecular beam
epitaxy (MBE) without foreign catalysts in the vapor-solid mode. The metal
shells are deposited by electron-beam evaporation in a metal MBE. High quality
supercondonductor/semiconductor hybrid structures such as Al/InAs and Nb/InAs
are of interest for ongoing research in the fields of gateable Josephson
junctions and quantum information related research. Systematic investigations
of the deposition parameters suitable for metal shell growth are conducted. In
case of Al, the substrate temperature, the growth rate and the shell thickness
are considered. The substrate temperature as well as the angle of the impinging
deposition flux are explored for Nb shells. The core-shell hybrid structures
are characterized by electron microscopy and x-ray spectroscopy. Our results
show that the substrate temperature is a crucial parameter in order to enable
the deposition of smooth Al layers. Contrary, Nb films are less dependent on
substrate temperature but strongly affected by the deposition angle. At a
temperature of 200{\deg}C Nb reacts with InAs, dissolving the nanowire crystal.
Our investigations result in smooth metal shells exhibiting an impurity and
defect free, crystalline superconductor/InAs interface. Additionally, we find
that the superconductor crystal structure is not affected by stacking faults
present in the InAs nanowires.Comment: 8 pages, 10 figures, 1 tabl
Tunable vector beam decoder by inverse design for high-dimensional quantum key distribution with 3D polarized spatial modes
Spatial modes of light have become highly attractive to increase the
dimension and, thereby, security and information capacity in quantum key
distribution (QKD). So far, only transverse electric field components have been
considered, while longitudinal polarization components have remained neglected.
Here, we present an approach to include all three spatial dimensions of
electric field oscillation in QKD by implementing our tunable, on-a-chip vector
beam decoder (VBD). This inversely designed device pioneers the "preparation"
and "measurement" of three-dimensionally polarized mutually unbiased basis
states for high-dimensional (HD) QKD and paves the way for the integration of
HD QKD with spatial modes in multifunctional on-a-chip photonics platforms.Comment: 10 pages, 3 figure
Plasmon induced thermoelectric effect in graphene
Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices
Emission enhancement of erbium in a reverse nanofocusing waveguide
Since Purcell's seminal report 75 years ago, electromagnetic resonators have
been used to control light-matter interactions to make brighter radiation
sources and unleash unprecedented control over quantum states of light and
matter. Indeed, optical resonators such as microcavities and plasmonic
nanostructures offer excellent control but only over a limited spectral range.
Strategies to tune both emission and the resonator are often required, which
preclude the possibility of enhancing multiple transitions simultaneously. In
this letter, we report a more than 590-fold radiative emission enhancement
across the telecommunications emission band of Erbium-ions in silica using a
single non-resonant plasmonic waveguide. Our plasmonic waveguide uses a novel
reverse nanofocusing approach to efficiently collect emission, making these
devices brighter than all non-plasmonic control samples considered. Remarkably,
the high broadband Purcell factor allows us to resolve the Stark-split electric
dipole transitions, which are typically only observed under cryogenic
conditions. Simultaneous Purcell enhancement of multiple quantum states is of
interest for photonic quantum networks as well as on-chip data communications
Near unity Raman -factor of surface enhanced Raman scattering in a waveguide
The Raman scattering of light by molecular vibrations offers a powerful
technique to 'fingerprint' molecules via their internal bonds and symmetries.
Since Raman scattering is weak, methods to enhance, direct and harness it are
highly desirable, e.g. through the use of optical cavities, waveguides, and
surface enhanced Raman scattering (SERS). While SERS offers dramatic
enhancements by localizing light within vanishingly small 'hot-spots' in
metallic nanostructures, these tiny interaction volumes are only sensitive to
few molecules, yielding weak signals that are difficult to detect. Here, we
show that SERS from 4-Aminothiophenol (4-ATP) molecules bonded to a plasmonic
gap waveguide is directed into a single mode with >99% efficiency. Although
sacrificing a confinement dimension, we find 10 times SERS enhancement
across a broad spectral range enabled by the waveguide's larger sensing volume
and non-resonant mode. Remarkably, the waveguide-SERS (W-SERS) is bright enough
to image Raman transport across the waveguides exposing the roles of
nanofocusing and the Purcell effect. Emulating the -factor from laser
physics, the near unity Raman -factor observed exposes the SERS
technique in a new light and points to alternative routes to controlling Raman
scattering. The ability of W-SERS to direct Raman scattering is relevant to
Raman sensors based on integrated photonics with applications in gas and
bio-sensing as well as healthcare.Comment: 12 pages, 4 figures in the main article; 12 pages, 7 figures in the
supplementary informatio