6 research outputs found
Sensing dot with high output swing for scalable baseband readout of spin qubits
A key requirement for quantum computing, in particular for a scalable quantum
computing architecture, is a fast and high-fidelity qubit readout. For
semiconductor based qubits, one limiting factor is the output swing of the
charge sensor. We demonstrate GaAs and Si/SiGe asymmetric sensing dots (ASDs),
which exceed the response of a conventional charge sensing dot by more than ten
times, resulting in a boosted output swing of . This
substantially improved output signal is due to a device design with a strongly
decoupled drain reservoir from the sensor dot, mitigating negative feedback
effects of conventional sensors. The large output signal eases the use of very
low-power readout amplifiers in close proximity to the qubit and will thus
render true scalable qubit architectures with semiconductor based qubits
possible in the future.Comment: 8 pages, 7 figure
Tailoring potentials by simulation-aided design of gate layouts for spin qubit applications
Gate-layouts of spin qubit devices are commonly adapted from previous
successful devices. As qubit numbers and the device complexity increase,
modelling new device layouts and optimizing for yield and performance becomes
necessary. Simulation tools from advanced semiconductor industry need to be
adapted for smaller structure sizes and electron numbers. Here, we present a
general approach for electrostatically modelling new spin qubit device layouts,
considering gate voltages, heterostructures, reservoirs and an applied
source-drain bias. Exemplified by a specific potential, we study the influence
of each parameter. We verify our model by indirectly probing the potential
landscape of two design implementations through transport measurements. We use
the simulations to identify critical design areas and optimize for robustness
with regard to influence and resolution limits of the fabrication process.Comment: 10 pages, 6 figure
Search for a RPV resonance in the \mu\tau final state at CMS
This bachelorthesis is about the search for a resonant, lepton number violating decay
of a tau sneutrino into the µτ final state. Only tau leptons which decay hadronically
are taken into account. This is done using 2015 CMS data with a center-of-mass
energy of 13 TeV and an integrated luminosity of 2.7 fb−1. Different types of tau
discriminators are studied and various kinematic cuts are applied to optimize the
signal to background ratio. As there is no sign for non standard model processes
in the final invariant µτ-mass distribution, a limit on the tau sneutrino mass is
calculated
Low-Temperature Ohmic Contacts to n -ZnSe for all-Electrical Quantum Devices
The II/VI semiconductor ZnSe is an ideal host for novel devices for quantum computation and communication as it can be made nuclear-spin free to obtain long electron spin coherence times, exhibits no electron valley-degeneracy, and allows optical access. A prerequisite to electrical quantum devices is low-resistive Ohmic contacts operating at temperatures below 10 K, which have not been achieved in ZnSe yet. Here, we present a comprehensive study on the realization of Ohmic contacts to ZnSe by three different technological approaches, ion implantation of halogen donors, epitaxial doping with in situ contact processing, and finally, a unique ZnSe regrowth technique. The latter allows fabrication of Ohmic contacts with local doping that can be used to connect to a buried conducting channel such as those used in unipolar devices. DC measurements revealed high contact resistivity for Ohmic contacts to ZnSe doped via halogene ion implantation, while in situ aluminum (Al) contacts on epitaxially chlorine-doped ZnSe yield record low contact resistivities in the order of 10–5 Ω cm2 even at cryogenic temperatures. Finally, making use of the regrowth technique, local Ohmic contacts to ZnSe are demonstrated, which still feature low contact resistivities of (1.4 ± 0.4) × 10–3 Ω cm2 at 4 K. These findings pave the way for new electrical devices in the ZnSe material system such as field-effect transistors, electrostatically defined qubits, or quantum repeaters operating at cryogenic temperatures
Local laser-induced solid-phase recrystallization of phosphorus-implanted Si/SiGe heterostructures for contacts below 4.2 K
Si/SiGe heterostructures are of high interest for high mobility transistor and qubit applications, specifically for operations below 4.2 K. In order to optimize parameters such as charge mobility, built-in strain, electrostatic disorder, charge noise and valley splitting, these heterostructures require Ge concentration profiles close to mono-layer precision. Ohmic contacts to undoped heterostructures are usually facilitated by a global annealing step activating implanted dopants, but compromising the carefully engineered layer stack due to atom diffusion and strain relaxation in the active device region. We demonstrate a local laser-based annealing process for recrystallization of ion-implanted contacts in SiGe, greatly reducing the thermal load on the active device area. To quickly adapt this process to the constantly evolving heterostructures, we deploy a calibration procedure based exclusively on optical inspection at room-temperature. We measure the electron mobility and contact resistance of laser annealed Hall bars at temperatures below 4.2 K and obtain values similar or superior than that of a globally annealed reference samples. This highlights the usefulness of laser-based annealing to take full advantage of high-performance Si/SiGe heterostructures