Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E29: Semiconductor Qubits  Quantum Computing with Donor Spins IFocus Live

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Sponsoring Units: DQI Chair: Matthew Donnelly, Univ of New South Wales 
Tuesday, March 16, 2021 8:00AM  8:12AM Live 
E29.00001: Firstprinciples calculations of hyperfine interaction, binding energy, and quadrupole coupling for shallow donors Michael Swift, Hartwin Peelaers, Sai Mu, Chris Van de Walle Shallow impurities are central to semiconductor technology. A thorough understanding of the physics of shallow impurities has taken on new urgency in the context of quantum information science, where they form key components of qubits. Because of the large spatial extent of the wave function, firstprinciples calculations of shallow centers have proved elusive. In addition, the “central cell corrections” that are crucial for accurately describing binding energies and hyperfine parameters are not adequately captured by traditional semilocal functionals in density functional theory, requiring advanced approaches that have proven too computationally demanding. We have developed a methodology that is capable of accurately predicting properties of shallow impurities. It is based on a combination of extrapolating results from supercell calculations carried out using a semilocal functional with performing select calculations using a hybrid functional. We will illustrate the power of this approach with results that provide an explanation for an observed unexpected strain dependence of the hyperfine properties of shallow donors in silicon, a system with applications in atomic clock transitions for siliconbased spin qubits. 
Tuesday, March 16, 2021 8:12AM  8:24AM Live 
E29.00002: Arrayed Quantum Dot Characterization in Si:P Quantum Devices Fan Fei, Xiqiao Wang, Ranjit Kashid, Jonathan Wyrick, Pradeep Namboodiri, Richard Silver STM based hydrogen lithography is a promising architecture for fabrication of atomicscale quantum devices. The precision of this technique allows placement of phosphorus atoms into predesigned lithography patterns with subnanometer resolution to form quantum dots. Structures such as double quantum dots or arrays of dopants in Si are a promising platform for analog quantum simulation of the FermiHubbard model. Design, fabrication and characterization of these devices is also useful for future multiqubit Si:Pbased quantum information processing. We present the design and fabrication of double/arrayed quantum dot devices. We compare low temperature transport measurements of the devices with a generalized Hubbard model and find it necessary to include inelastic processes. We extract interdot tunnel coupling of a double dot device and demonstrate interesting rectifying behavior. For devices with more than 2 dots, we found disorder is currently inevitable and is crucial to device transport properties. In our Si:P devices, gates/leads are capacitively coupled to the central dot region. Large gate ranges and linear capacitance coupling are essential to producing good finite bias spectroscopy. We will describe fabrication developments to improve device gating performance. 
Tuesday, March 16, 2021 8:24AM  8:36AM Live 
E29.00003: A chemical model for atomicprecision singledonor incorporation of phosphorus atoms in Si(100)2x1 Quinn Campbell, Jeffrey Ivie, Justin Koepke, Mitchell Brickson, Peter Schultz, Richard Muller, Ezra Bussmann, Andrew D Baczewski, Andrew M Mounce, Shashank Misra Understanding the statistics of atomicprecision singlephosphorus atom incorporation on Si(100)2x1 is crucial to the development of analog quantum simulation devices. One method for creating such devices is to use a scanning tunneling microscope to depassivate a fewatom region on Hterminated Si, which is then exposed to a precursor gas that subsequently dissociates such that a donor is incorporated through some chemical pathway. In this talk, we develop a kinetic Monte Carlo model of this process parameterized from first principles calculations to predict the incorporation statistics as a function of the initial depassivation geometry, temperature at dosing and anneal, and pressure of precursor gas. Using our model, we match experimentally measured rates of incorporation and suggest future pathways for the improvement of incorporation rates. 
Tuesday, March 16, 2021 8:36AM  8:48AM Live 
E29.00004: Transition metal impurities in Silicon: Computational search for semiconductor qubit ChengWei Lee, Adele Tamboli, Meenakshi Singh, Vladan Stevanovic Two classical impuritysemiconductor qubits are ^{31}P in silicon and NV^{} center in diamond, both of which have their own strengths and weaknesses. The spin subsystem of ^{31}P in Si requires extremely low temperature to initialize while in case of the NV^{} center, it is initialized by the nonradiative transition, which allows higher operating temperatures. However, diamond manufacturing is not as mature as Si. Herein, we search for candidate Sibased impuritysemiconductor qubits that could benefit from the established silicon technology but with higher operating temperature. Since transition metal impurities are known to form deep states in crystalline Si, we conduct a survey of all 3d and selected heavier transition metals using modern firstprinciples defect calculations with the purpose of predicting location and spin of defect levels. Specifically, we applied the wellestablished supercell approach and HSE06 hybrid functional, which accurately reproduces band gap of Si as well as localization of defect states. As a result, we find several candidate impurities that form spin triplet defect states within the electronic bandgap with C_{3v} symmetry. These candidate systems resemble the NV^{} center in diamond and hold the potential to operate at higher temperature. 
Tuesday, March 16, 2021 8:48AM  9:00AM Live 
E29.00005: Understanding chargestability diagrams of dopant arrays in Si Garnett Bryant, Emily Townsend, Maicol Ochoa, Fan Fei, Xiqiao Wang, Richard Silver Atomically precise fabrication of dopant arrays in Si provides exciting opportunities to perform quantum simulations, study the dynamics of engineered quantum systems, and develop atomicscale quantum materials. We describe theoretical simulations done for twodimensional arrays of dopants in Si implemented with an extended range FermiHubbard model and supported by atomistic modelling of the array states. Simulations are done with and without dopant disorder, as a function of the electronelectron interaction to test the limits of weak and strong interaction. Hund’s rule defines the nature of the charged array ground states for large onsite electronelectron repulsion. Ground states for charged arrays can be highly (quasi) degenerate, providing multiple transport channels. Disorder splits these degeneracies, helping define the charge boundaries in chargestability diagrams. We consider n x m arrays of different sizes to identify the array states that are probed in transport. Results are used to understand chargestability diagrams recently obtained for twodimensional arrays of dopants in Si. Implications for using dopant arrays as a quantum lab on a chip are discussed. 
Tuesday, March 16, 2021 9:00AM  9:12AM Live 
E29.00006: Tunneling Statistics and Spin Readout of Fewdonor Quantum Dots in Silicon Xiqiao Wang, Ranjit Kashid, Jonathan Wyrick, Fan Fei, Pradeep Namboodiri, Albert Rigosi, Richard Silver The long electron spin coherence and relaxation times achievable in donorbased quantum dots in silicon provide a promising route towards scalable solidstate quantum computation. Highfidelity singleshot spin readout and initialization are essential for implementing faulttolerant quantum algorithms. However, unwanted dynamic interactions between the quantum dot electron and its environment and charge sensor can significantly limit the spin readout fidelity. Here we present our recent spin readout and initialization measurements in fewdonor cluster quantum dots using STMpatterned singleelectron transistor charge sensors in the strong response regime. Using spectroscopic measurements of singleelectron loading/unloading rates and analysis of spinselective tunneling statistics, we investigate the charge and spin dynamics between the fewdonor quantum dot and charge sensor where spintocharge conversion and random telegraph switching occur. We discuss the impact of charge noise and the charge sensor's density of states fluctuations on the spinstate readout and initialization, as well as perspectives on device design, fabrication, and measurement conditions to optimize spinreadout fidelity for robust single electron spin qubit manipulation. 
Tuesday, March 16, 2021 9:12AM  9:24AM Live 
E29.00007: Properties of shallow donor ensembles in ZnO for quantum memory applications Vasileios Niaouris, Christian Zimmermann, Xiayu Linpeng, Maria L. K. Viitaniemi, Yusuke Kozuka, Masashi Kawasaki, KaiMei Fu Neutral shallow donors (D^{0}) in ZnO, such as Al_{Zn}, Ga_{Zn}, In_{Zn,} are promising solidstate spin qubits^{1}. D^{0} optically couples to the neutral donor bound exciton (D^{0}X) with high radiative efficiency, potentially enabling photonmediated quantum entanglement schemes both between donors, and donors and trappedions^{2}. Here we report on the optical ensemble properties of ZnO donors, toward quantum memory applications (QMA). The optical D^{0}X transition exhibits an inhomogeneous linewidth of 20 GHz measured via photoluminescence excitation, and optical absorption. The 0field optical depth (OD) for the Al and Ga transitions is 10 and 6, respectively, and dramatically decreases at field due to optical pumping. We will further present spectral hole burning measurements to determine the upper bound homogeneous linewidth and discuss the diffrent line broadening contributions. The large OD, homogeneous optical properties and potential to extend spincoherence times indicate ZnO donor ensembles are promising for QMA. 
Tuesday, March 16, 2021 9:24AM  9:36AM Live 
E29.00008: The electronic structure and transport properties of phosphorus arrays and phosphorus clusters in silicon nanodevices. Maicol Ochoa, Keyi Liu, Emily Townsend, Michal Gawelczyk, Michal Zielinski, Garnett Bryant Donorbased quantum devices in silicon are attractive for universal quantum computing and analog quantum simulations, providing great control over the quantum states of these devices. We present theoretical atomistic calculations and a detailed analysis of the electronic and transport properties of phosphorus dopant arrays and clusters in Si quantum devices. Our method consists of selfconsistent calculations of the electron energy levels in Pdoped Si devices using representative tightbinding Hamiltonians with solutions to the Poisson equation to account for external potentials. We identify the electronic states and charge distribution in linear, triangular, and square dopant arrays of different sizes and under the influence of a range of gate and source/drain potentials. We rationalize our findings in terms of dopant wavefunction overlaps, symmetries of electronic states, and grouptheory methods. For large dopant spacing, arrays act as weaklycoupled distinct sites. For small dopant spacing, arrays act as giant clusters. We identify this transition and discuss how it affects transport. Our simulations allow us to understand the stability diagrams in these devices, demonstrating that our approach accurately describes transport through multidopant quantum devices. 
Tuesday, March 16, 2021 9:36AM  10:12AM Live 
E29.00009: AtomBased Silicon Devices for Quantum Computing and Analog Quantum Simulation Invited Speaker: Richard Silver NIST is using atomically precise fabrication to develop devices for use in quantum information 
Tuesday, March 16, 2021 10:12AM  10:24AM Live 
E29.00010: The improved pointcharge model for dopants in Si and applications to atomicscale system simulations Keyi Liu, Piotr T. Rozanski, Michal Zielinski, Garnett Bryant Dopants in silicon are strong candidates for qubits in scalable solidstate quantum systems. Tightbinding (TB) theory has been used to provide a good atomicscale model when a central cell correction is fit to experimental binding energies for one choice of the bulk Si TB parameters. However, this model fails to predict the correct dopant level energy degeneracies for other wellestablished TB models. We argue that the pointcharge dopant model with a simple central cell correction is missing vital contributions from the dopant potential. We have developed a first principlesbased dopant model with several new corrections that are obtained explicitly through selfconsistent field calculations to evaluate the appropriate dopant matrix elements rather than by fitting to experiment. We find that these new corrections greatly improve our predictability of the underlying dopant physics, as all bulk Si TB parameters produce the correct ordering of dopant levels in our new model, and give us flexible tunability of numerical values of the dopant level to arbitrary precision. Results are discussed to show the effect on interdopant exchange coupling and the level structure of dopant clusters. Finally, we discuss how these models can effectively simulate manybody physics in atom arrays. 
Tuesday, March 16, 2021 10:24AM  10:36AM Live 
E29.00011: The impact of donor incorporation statistics on analog quantum simulations of Hubbard physics in nearatomic precision donor arrays Mitchell Brickson, Quinn Campbell, Jeffrey Ivie, Justin Koepke, Peter Schultz, Richard Muller, Ezra Bussmann, Andrew D Baczewski, Shashank Misra Atomic precision advanced manufacturing (APAM) is a promising approach for analog quantum simulation of strongly correlated systems. APAM relies on scanning tunneling microscope lithography to place single P donors precisely in Si. Assessing the impact of experimentally demonstrated stochastic donor incorporation on device performance is vital to understanding the limits of analog quantum simulation. Using a nonequilibrium Green’s function formalism, we simulate transport characteristics of Hubbard models basedon P donors in Si, and the effects of probabilistic donor incorporation on these transport characteristics. Using our model, we find limits on the Hamiltonians one can target without losing prominent physical features of the model to missing donors. 
Tuesday, March 16, 2021 10:36AM  10:48AM Live 
E29.00012: Digital Hydrogen Depassivation Lithography for Improving Precison of Donor Placement in Si John Randall, James H.G. Owen, Ehud Fuchs, Robin Santini Hydrogen depassivation lithography (HDL) has been used to place dopants on the Si surface for Si donor qubits, single electron transistors^{1}, and shows promise for analog quantum simulation devices^{2}. We use image analysis to identify lithography pixels which are defined as two dimers along a dimer row^{3}. During lithography, the tip moves over the pixels to be exposed, following vectors defined from the device pattern. There is a tip position tolerance of +/ 1.3Å. However, thermal drift, tip changes, creep, and hysteresis all make keeping this tolerance during lithography difficult. 
Tuesday, March 16, 2021 10:48AM  11:00AM Live 
E29.00013: Dopant Precursor Adsorption into a SingleDimer Window on Si(100): Computational Screening of PrecursorResist Combinations Matthew Radue, Yifei Mo, Robert E Butera Envisioned spinbased quantum computers present the tremendous fabrication challenge of creating an atomically precise dopant array in Si. To meet this challenge, lithographic strategies have been successfully developed to incorporate a single phosphorus atom within a fewdimer window on Si(100). A growing number of dopant precursors, including acceptors for holebased qubits and superconducting Si devices, and resists, such as halogens in place of hydrogen, are being explored to further expand the application space for atomicprecision fabrication. While recent ideas posit the use of singledimer windows to control dopant placement, whether or not the precursor will “fit” into such a tight window has yet to be explored for new lithographic material systems. This is especially uncertain for relatively large precursors combined with relatively large resist atoms. In this study, density functional theory is used to calculate the initial adsorption configurations and adsorption pathways of common acceptor and donor precursors into a singledimer window. Various resist atoms are used to identify which precursorresist combinations are precluded on the basis of steric hindrances. 
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