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Lithographic quantum dots for quantum computation and quantum simulation

Brickson, Mitchell I.; Baczewski, Andrew D.

Lithographic quantum dots (QDs) are highly controllable few-level quantum systems created in semiconductor nanoelectronic devices, with a variety of scientific applications. These include technologically-driven applications like quantum computing and more fundamental applications in which they serve as a platform for exploring basic many-body physics. This document is a brief summary of my Ph.D. research so far and the directions with which I intend to continue it. Highlights include theoretical efforts to understand and design qubits in germanium hole QDs, as well as explorations of the possibility of using QDs coupled to nearby baths for analog simulation of quantum impurity models.

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TYPE Other Report YEAR 2020
DOIOSTI

Designer quantum materials

Misra, Shashank; Ward, Daniel R.; Baczewski, Andrew D.; Campbell, Quinn; Schmucker, Scott W.; Mounce, Andrew M.; Tracy, Lisa A.; Lu, Tzu M.; Marshall, Michael; Campbell, Deanna M.

Quantum materials have long promised to revolutionize everything from energy transmission (high temperature superconductors) to both quantum and classical information systems (topological materials). However, their discovery and application has proceeded in an Edisonian fashion due to both an incomplete theoretical understanding and the difficulty of growing and purifying new materials. This project leverages Sandia's unique atomic precision advanced manufacturing (APAM) capability to design small-scale tunable arrays (designer materials) made of donors in silicon. Their low-energy electronic behavior can mimic quantum materials, and can be tuned by changing the fabrication parameters for the array, thereby enabling the discovery of materials systems which can't yet be synthesized. In this report, we detail three key advances we have made towards development of designer quantum materials. First are advances both in APAM technique and underlying mechanisms required to realize high-yielding donor arrays. Second is the first-ever observation of distinct phases in this material system, manifest in disordered 2D sheets of donors. Finally are advances in modeling the electronic structure of donor clusters and regular structures incorporating them, critical to understanding whether an array is expected to show interesting physics. Combined, these establish the baseline knowledge required to manifest the strongly-correlated phases of the Mott-Hubbard model in donor arrays, the first step to deploying APAM donor arrays as analogues of quantum materials.

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TYPE SAND Report YEAR 2019
DOIOSTI

Gate-defined quantum dots in Ge/SiGe quantum wells as a platform for spin qubits

ECS Transactions

Hardy, Will; Su, Y.H.; Chuang, Y.; Maurer, Leon; Brickson, Mitchell I.; Baczewski, Andrew D.; Li, J.Y.; Lu, Tzu M.; Luhman, Dwight R.

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel qubits. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells, consisting of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below. These quantum wells feature heavy hole carriers and a cubic Rashba-type spin-orbit interaction. Here, we describe progress toward realizing spin qubits in this platform, including development of multi-metal-layer gated device architectures, device tuning protocols, and charge-sensing capabilities. Iterative improvement of a three-layer metal gate architecture has significantly enhanced device performance over that achieved using an earlier single-layer gate design. We discuss ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a single-spin qubit demonstration.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

Gate-defined quantum dots in Ge/SiGe quantum wells as a platform for spin qubits

ECS Transactions

Hardy, Will; Su, Y.H.; Chuang, Y.; Maurer, Leon; Brickson, Mitchell I.; Baczewski, Andrew D.; Li, J.Y.; Lu, Tzu M.; Luhman, Dwight R.

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel qubits. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells, consisting of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below. These quantum wells feature heavy hole carriers and a cubic Rashba-type spin-orbit interaction. Here, we describe progress toward realizing spin qubits in this platform, including development of multi-metal-layer gated device architectures, device tuning protocols, and charge-sensing capabilities. Iterative improvement of a three-layer metal gate architecture has significantly enhanced device performance over that achieved using an earlier single-layer gate design. We discuss ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a single-spin qubit demonstration.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus

A silicon metal-oxide-semiconductor electron spin-orbit qubit

Nature Communications

Jock, Ryan M.; Jacobson, Noah T.; Harvey-Collard, Patrick; Mounce, Andrew M.; Srinivasa, Vanita; Ward, Daniel R.; Anderson, John M.; Manginell, Ronald; Wendt, Joel R.; Rudolph, Martin; Pluym, Tammy; Foulk, James W.; Baczewski, Andrew D.; Witzel, Wayne M.; Carroll, M.S.

The silicon metal-oxide-semiconductor (MOS) material system is a technologically important implementation of spin-based quantum information processing. However, the MOS interface is imperfect leading to concerns about 1/f trap noise and variability in the electron g-factor due to spin-orbit (SO) effects. Here we advantageously use interface-SO coupling for a critical control axis in a double-quantum-dot singlet-triplet qubit. The magnetic fieldorientation dependence of the g-factors is consistent with Rashba and Dresselhaus interface-SO contributions. The resulting all-electrical, two-Axis control is also used to probe the MOS interface noise. The measured inhomogeneous dephasing time, T2m, of 1.6 ?s is consistent with 99.95% 28Si enrichment. Furthermore, when tuned to be sensitive to exchange fluctuations, a quasi-static charge noise detuning variance of 2 μeV is observed, competitive with low-noise reports in other semiconductor qubits. This work, therefore, demonstrates that the MOS interface inherently provides properties for two-Axis qubit control, while not increasing noise relative to other material choices.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Weak anti-localization of two-dimensional holes in germanium beyond the diffusive regime

Nanoscale

Chou, C.T.; Jacobson, Noah T.; Moussa, J.E.; Baczewski, Andrew D.; Chuang, Y.; Liu, C.Y.; Li, J.Y.; Lu, Tzu M.

Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than ∼6 × 1011 cm-2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus
Results 101–150 of 243
Results 101–150 of 243