A5032729093- Advancements in Semiconductor Devices and Circuit Design
- Semiconductor Quantum Structures and Devices
- Quantum and electron transport phenomena
- Semiconductor materials and devices
- Photonic and Optical Devices
- Advanced Materials Characterization Techniques
- Surface and Thin Film Phenomena
- Semiconductor materials and interfaces
- Topological Materials and Phenomena
- Semiconductor Lasers and Optical Devices
- Silicon Nanostructures and Photoluminescence
- Quantum Computing Algorithms and Architecture
- GaN-based semiconductor devices and materials
- Magneto-Optical Properties and Applications
- Spectroscopy and Quantum Chemical Studies
- Ion-surface interactions and analysis
- Electronic and Structural Properties of Oxides
University of Wisconsin–Madison
2020-2024
Abstract Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom formation qubits. Despite attempts to enhance valley energy splitting deterministically, by engineering a sharp interface, fluctuations remain serious problem for qubit uniformity, needed scale up large processors. Here, we elucidate and statistically predict holistic integration 3D atomic-level properties, theory transport. We find that...
Abstract Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance splitting rely on sharp interfaces modifications well barriers that can be difficult grow. Here, we propose and demonstrate a new heterostructure, “Wiggle Well”, whose key feature is Ge concentration oscillations inside well. Experimentally, show placing...
Silicon/silicon-germanium heterostructures have many important advantages for hosting spin qubits. However, controlling the valley splitting (the energy between two low-lying conduction-band valleys) remains a critical challenge ensuring qubit reliability. Broad distributions of splittings are commonplace, even among quantum dots formed on same chip. In this work, we theoretically explore interplay quantum-well imperfections that suppress and cause variability, such as broadened interfaces...
The energies of valley-orbit states in silicon quantum dots are determined by an as yet poorly understood interplay between interface roughness, orbital confinement, and electron interactions. Here, we report measurements one- two-electron state the dot potential is modified changing gate voltages, calculate these same using full configuration interaction calculations. results enable understanding physical contributions a new probe well interface.
Coherent coupling between distant qubits is needed for many scalable quantum computing schemes. In dot systems, one proposal long-distance to coherently transfer electron spins across a chip in moving potential. Here, we use simulations study challenges spin shuttling <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mi>Si</a:mi></a:math>/<d:math xmlns:d="http://www.w3.org/1998/Math/MathML" overflow="scroll"><d:mi>Si</d:mi></d:math><g:math...
We determine the energy splitting of conduction-band valleys in two-dimensional electrons confined to low-disorder Si quantum wells. probe valley dependence on both perpendicular magnetic field $B$ and Hall density by performing activation measurements regime over a large range filling factors. The mobility gap valley-split levels increases linearly with is strikingly independent density. data are consistent transport model which depends incremental changes $eB/h$ across edge strips, rather...
Abstract Understanding crystal characteristics down to the atomistic level increasingly emerges as a crucial insight for creating solid state platforms qubits with reproducible and homogeneous properties. Here, isotope concentration depth profiles in SiGe/ 28 Si/SiGe heterostructure are analyzed atom probe tomography (APT) time‐of‐flight secondary‐ion mass spectrometry their respective limits of concentrations resolution. Spin‐echo dephasing times valley energy splittings E VS around have...
Coherent coupling between distant qubits is needed for any scalable quantum computing scheme. In dot systems, one proposal long-distance to coherently transfer electron spins across a chip in moving potential. Here, we use simulations study challenges spin shuttling Si/SiGe heterostructures caused by the valley degree of freedom. We show that devices with splitting dominated alloy disorder, can expect encounter pockets low splitting, given long-enough path. At such locations, inter-valley...
Conveyor-mode shuttling is a key approach for implementing intermediate-range coupling between electron-spin qubits in quantum dots. Initial results are encouraging; however, long trajectories guaranteed to encounter regions of low conduction-band valley energy splittings, due the presence random-alloy disorder Si/SiGe wells. Here, we theoretically explore two schemes avoiding valley-state excitations at these minima, by allowing electrons detour around them. The multichannel scheme allows...
Nanofabricated metal gate electrodes are commonly used to confine and control electrons in electrostatically defined quantum dots. However, these same gates impart a complicated strain geometry that affects the confinement potential potentially impairs device functionality. Here we investigate strain-induced fluctuations of energy Si/SiGe heterostructures, caused by (i) lattice mismatch, (ii) materials-dependent thermal contraction, (iii) deposition stress gates. By simulating different...
Understanding crystal characteristics down to the atomistic level increasingly emerges as a crucial insight for creating solid state platforms qubits with reproducible and homogeneous properties. Here, isotope composition depth profiles in SiGe/$^{28}$Si/SiGe heterostructure are analyzed atom probe tomography (APT) time-of-flight secondary-ion mass spectrometry. Spin-echo dephasing times $T_2^{echo}=128 \mu s$ valley energy splittings around $200 eV$ have been observed single spin this...
We present a scalable protocol for suppressing errors during electron spin shuttling in silicon quantum dots. The approach maps the valley Hamiltonian to Landau-Zener problem model nonadiabatic dynamics regions of small splitting. An optimization refines velocity profile over single segment path. reliably returns state ground at end shuttle, disentangling and degrees freedom, after which virtual $z$-rotation on compensates its evolution shuttle. time cost complexity error suppression is...
Understanding the $g$-factor physics of Si/SiGe quantum dots is crucial for realizing high-quality spin qubits. While previous work has explained some aspects in idealized geometries, results do not extend to general cases and they miss several important features. Here, we construct a theory that gives $g$ terms readily computable matrix elements, can be applied all heterostructures current interest. As concrete example, which currently no understanding, study so-called Wiggle Well...
Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom formation qubits. Despite attempts to enhance valley energy splitting deterministically, by engineering a sharp interface, fluctuations remain serious problem for qubit uniformity, needed scale up large processors. Here, we elucidate and statistically predict holistic integration 3D atomic-level properties, theory transport. We find that concentration...
Silicon/silicon-germanium heterostructures have many important advantages for hosting spin qubits. However, controlling the valley splitting (the energy between two low-lying conduction-band valleys) remains a critical challenge ensuring qubit reliability. Broad distributions of splittings are commonplace, even among quantum dots formed on same chip. In this work, we theoretically explore interplay quantum-well imperfections that suppress and cause variability, such as broadened interfaces...
Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance splitting rely on sharp interfaces modifications well barriers that can be difficult grow. Here, we propose and demonstrate a new heterostructure, "Wiggle Well," whose key feature is Ge concentration oscillations inside well. Experimentally, show placing does not...