85 research outputs found
Tunable capacitive inter-dot coupling in a bilayer graphene double quantum dot
We report on a double quantum dot which is formed in a width-modulated etched
bilayer graphene nanoribbon. A number of lateral graphene gates enable us to
tune the quantum dot energy levels and the tunneling barriers of the device
over a wide energy range. Charge stability diagrams and in particular
individual triple point pairs allow to study the tunable capacitive inter-dot
coupling energy as well as the spectrum of the electronic excited states on a
number of individual triple points. We extract a mutual capacitive inter-dot
coupling in the range of 2 - 6 meV and an inter-dot tunnel coupling on the
order of 1.5 {\mu}eV.Comment: 6 pages, 4 figure
Si/SiGe QuBus for single electron information-processing devices with memory and micron-scale connectivity function
The connectivity within single carrier information-processing devices
requires transport and storage of single charge quanta. Our all-electrical
Si/SiGe shuttle device, called quantum bus (QuBus), spans a length of 10
m and is operated by only six simply-tunable voltage pulses. It
operates in conveyor-mode, i.e. the electron is adiabatically transported while
confined to a moving QD. We introduce a characterization method, called
shuttle-tomography, to benchmark the potential imperfections and local
shuttle-fidelity of the QuBus. The fidelity of the single-electron shuttle
across the full device and back (a total distance of 19 m) is
. Using the QuBus, we position and detect up to 34
electrons and initialize a register of 34 quantum dots with arbitrarily chosen
patterns of zero and single-electrons. The simple operation signals,
compatibility with industry fabrication and low spin-environment-interaction in
Si/SiGe, promises spin-conserving transport of spin qubits for quantum
connectivity in quantum computing architectures.Comment: 11 pages, 6 figure
Spin-EPR-pair separation by conveyor-mode single electron shuttling in Si/SiGe
Long-ranged coherent qubit coupling is a missing function block for scaling
up spin qubit based quantum computing solutions. Spin-coherent conveyor-mode
electron-shuttling could enable spin quantum-chips with scalable and sparse
qubit-architecture. Its key feature is the operation by only few easily
tuneable input terminals and compatibility with industrial gate-fabrication.
Single electron shuttling in conveyor-mode in a 420 nm long quantum bus has
been demonstrated previously. Here we investigate the spin coherence during
conveyor-mode shuttling by separation and rejoining an Einstein-Podolsky-Rosen
(EPR) spin-pair. Compared to previous work we boost the shuttle velocity by a
factor of 10000. We observe a rising spin-qubit dephasing time with the longer
shuttle distances due to motional narrowing and estimate the spin-shuttle
infidelity due to dephasing to be 0.7 % for a total shuttle distance of nominal
560 nm. Shuttling several loops up to an accumulated distance of 3.36 m,
spin-entanglement of the EPR pair is still detectable, giving good perspective
for our approach of a shuttle-based scalable quantum computing architecture in
silicon
Two-dimensional photonic crystal cavities in ZnSe quantum well structures
ZnSe and related materials like ZnMgSe and ZnCdSe are promising II-VI host
materials for optically mediated quantum information technology such as single
photon sources or spin qubits. Integrating these heterostructures into photonic
crystal (PC) cavities enables further improvements, for example realizing
Purcell-enhanced single photon sources with increased quantum efficiency. Here
we report on the successful implementation of two-dimensional (2D) PC cavities
in strained ZnSe quantum wells (QW) on top of a novel AlAs supporting layer.
This approach overcomes typical obstacles associated with PC membrane
fabrication in strained materials, such as cracks and strain relaxation in the
corresponding devices. We demonstrate the attainment of the required mechanical
stability in our PC devices, complete strain retainment and effective vertical
optical confinement. Structural analysis of our PC cavities reveals excellent
etching anisotropy. Additionally, elemental mapping in a scanning transmission
electron microscope confirms the transformation of AlAs into AlOx by
post-growth wet oxidation and reveals partial oxidation of ZnMgSe at the etched
sidewalls in the PC. This knowledge is utilized to tailor FDTD simulations and
to extract the ZnMgSe dispersion relation with small oxygen content. Optical
characterization of the PC cavities with cross-polarized resonance scattering
spectroscopy verifies the presence of cavity modes. The excellent agreement
between simulation and measured cavity mode energies demonstrates wide
tunability of the PC cavity and proves the pertinence of our model. This
implementation of 2D PC cavities in the ZnSe material system establishes a
solid foundation for future developments of ZnSe quantum devices
Electron-hole crossover in gate-controlled bilayer graphene quantum dots
Electron and hole Bloch states in gapped bilayer graphene exhibit topological
orbital magnetic moments with opposite signs near the band edges, which allows
for tunable valley-polarization in an out-of-plane magnetic field. This
intrinsic property makes electron and hole quantum dots (QDs) in bilayer
graphene interesting for valley and spin-valley qubits. Here we show
measurements of the electron-hole crossover in a bilayer graphene QD,
demonstrating the opposite sign of the orbital magnetic moments associated with
the Berry curvature. Using three layers of metallic top gates, we independently
control the tunneling barriers of the QD while tuning the occupation from the
few-hole regime to the few-electron regime, crossing the displacement-field
controlled band gap. The band gap is around 25 meV, while the charging energies
of the electron and hole dots are between 3-5 meV. The extracted valley
g-factor is around 17 and leads to opposite valley polarization for electron
and hole states at moderate B-fields. Our measurements agree well with
tight-binding calculations for our device
Single in situ Interface Characterization Composed of Niobium and a Selectively Grown (BiSb)Te Topological Insulator Nanoribbon
With increasing attention in Majorana physics for possible quantum bit
applications, a large interest has been developed to understand the properties
of the interface between a -type superconductor and a topological insulator.
Up to this point the interface analysis was mainly focused on in situ prepared
Josephson junctions, which consist of two coupled single interfaces or to
ex-situ fabricated single interface devices. In our work we utilize a novel
fabrication process, combining selective area growth and shadow evaporation
which allows the characterization of a single in situ fabricated
Nb/ nano interface. The resulting high
interface transparency is apparent by a zero bias conductance increase by a
factor of 1.7. Furthermore, we present a comprehensive differential conductance
analysis of our single in situ interface for various magnetic fields,
temperatures and gate voltages. Additionally, density functional theory
calculations of the superconductor/topological insulator interface are
performed in order to explain the peak-like shape of our differential
conductance spectra and the origin of the observed smearing of conductance
features.Comment: Main manuscript: 11 pages, 6 figures, Supplementary material: 10
pages, 9 figure
Integration of selectively grown topological insulator nanoribbons in superconducting quantum circuits
We report on the precise integration of nm-scale topological insulator
Josephson junctions into mm-scale superconducting quantum circuits via
selective area epitaxy and local stencil lithography. By studying dielectric
losses of superconducting microwave resonators fabricated on top of our
selective area growth mask, we verify the compatibility of this in situ
technique with microwave applications. We probe the microwave response of
on-chip microwave cavities coupled to topological insulator-shunted
superconducting qubit devices and observe a power dependence that indicates
nonlinear qubit behaviour. Our method enables integration of complex networks
of topological insulator nanostructures into superconducting circuits, paving
the way for both novel voltage-controlled Josephson and topological qubits.Comment: 11 pages, 6 figure
Níveis de lisina digestível em rações, em que se manteve ou não a relação aminoacídica, para frangos de corte de 1 a 21 dias de idade, mantidos em estresse por calor
Dois ensaios foram conduzidos para avaliar os efeitos de níveis de lisina digestível em rações em que se manteve ou não a relação aminoacídica sobre o desempenho de frangos de corte machos de 1 a 21 dias de idade, criados em alta temperatura. O delineamento experimental utilizado em ambos os ensaios foi o inteiramente casualizado. As aves, no ensaio 1, foram distribuídas em cinco tratamentos (0,92; 0,98; 1,04; 1,10 e 1,16% de lisina digestível em ração convencional), oito repetições e dez aves por repetição. No ensaio 2, os frangos foram distribuídos em quatro tratamentos (1,04; 1,10; 1,16 e 1,22% de lisina digestível em rações mantendo a relação aminoacídica), oito repetições e dez aves por repetição. No ensaio 1, os tratamentos influenciaram quadraticamente o ganho de peso e o consumo de ração, que aumentaram até os níveis de 1,14 e 1,09% de lisina, respectivamente. Embora a conversão alimentar tenha melhorado de forma linear, o modelo LRP foi o que melhor se ajustou aos dados, estimando em 1,097% o nível de lisina a partir do qual ocorreu um platô. Não houve efeito dos tratamentos sobre os pesos absolutos do coração, fígado e intestinos, enquanto o peso absoluto da moela aumentou linearmente. O peso absoluto da carcaça aumentou, enquanto os pesos relativos do coração e do fígado reduziram quadraticamente com os tratamentos. No ensaio 2, os tratamentos influenciaram de forma linear crescente o ganho de peso e a conversão alimentar, enquanto o consumo de ração não variou. Os tratamentos influenciaram linearmente o peso absoluto da carcaça, enquanto os pesos absoluto e relativo das vísceras não variaram. Concluiu-se que frangos de corte machos, de 1 a 21 dias de idade, mantidos em estresse por calor, exigem, no mínimo, 1,14 e 1,22% de lisina digestível em ração convencional e em ração em que se manteve a relação aminoacídica, respectivamente.Two trials were conducted to evaluate the effects of digestible lysine levels in diets maintaining or not the relationship of amino acids, on performance of broilers from 1 to 21 days, kept under heat stress. A completely randomized experimental design was used in both trials. In the trial 1, the broilers were allotted in five treatments (0.92; 0.98; 1.04; 1.10 and 1.16% of lysine in conventional diets), eight replicates and ten broilers per replicate. In the trial 2, the broilers were allotted in four treatments (1.04; 1.10; 1.16 and 1.22% of lysine in diet maintaining the relationship of amino acids), eight replicates and ten broilers per replicate. In the trial 1, the digestible lysine levels influenced quadraticly the weight gain and the feed intake that increased up to 1.14 and 1.09%, respectively. Although feed:gain ratio had changed by linear way, the LRP model adjusted better to the data, estimating in 1.097% the lysine level where occurred a "plateau". There was no effect of treatments on absolute weights of heart, liver and intestines, while the absolute weight of gizzard increased linearly. The absolute weight of carcass increased while the relative weights of heart and liver reduced quadraticly. In the trial 2, the treatments influenced in a crescent linear way the weight gain and the feed:gain ratio while the feed intake was not influenced. The treatments influenced linearly the absolute weight of carcass while the absolute and relative weights of the organs were not influenced. It was concluded that male broilers, in the period from 1 to 21 days of age, kept under heat stress, require at least 1.14 and 1.22% of digestible lysine in conventional diet and in diet maintaining the relationship of amino acid, respectively
Entwicklung und Charakterisierung vertikaler Double-Gate-MOS-Feldeffekttransistoren
Planar MOS-field-effect transistors are common devices today used by the computer industry. When their miniaturization reaches its limit, alternate transistor concepts become necessary. In this thesis the development of vertical Double-Gate-MOS-field-effect transistors is presented. These types of transistors have a vertically aligned p-n-p junction (or n-p-n junction, respectively). Consequently, the source-drain current flows perpendicular with respect to the surface of the wafer. A Double-Gate-field-effect transistor is characterized by a very thin channel region framed by two parallel gates. Due to the symmetry of the structure and less bulk volume better gate control and hence better short channel behavior is expected, as well as an improved scaling potential. Nanostructuring of the transistor's active region is very challenging. Approximately 300 nm high and down to 30 nm wide silicon ridges are requisite. They can be realized using hydrogen silsesquioxane (HSQ) as inorganic high resolution resist for electron beam lithography. Structures defined in HSQ are then transferred with high anisotropy and selectivity into silicon using ICP-RIE (reactive ion etching with inductive coupled plasma). 25 nm wide and 330 nm high silicon ridges are achieved. Different transistor layouts are realized. The channel length is defined by epitaxial growth of doped silicon layers before or by ion implantation after nanostructuring, respectively. The transistors show source-drain currents up to 380 A/m and transconductances up to 480 pS/pm. Improved short channel behavior for decreasing width of the silicon ridges is demonstrated
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