Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P17: Quantum Computing with Donor SpinsFocus

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Sponsoring Units: DQI Chair: RUICHEN ZHAO, National Institute of Standards and Technology Boulder Room: 203 
Wednesday, March 4, 2020 2:30PM  3:06PM 
P17.00001: Demonstration and benchmarking of electron and nuclear 2qubit logic gates with implanted donors in silicon Invited Speaker: Andrea Morello Ionimplanted ^{31}P donors in silicon have attained 1qubit gate fidelities >99.9% [1]. 
Wednesday, March 4, 2020 3:06PM  3:18PM 
P17.00002: Driven dynamics of an electron coupled to spin3/2 nuclei in quantum dots Arian Vezvaee, Girish Sharma, Sophia Economou, Edwin Barnes The problem of hyperfine interaction between a confined electron in a selfassembled quantum dot and its surrounding nuclear spin environment features interesting physics. Driving of the electron spin leads to dynamic nuclear spin polarization of the bath, and feedback effects on the electron spin can qualitatively change its dynamics. While for most systems of interest the nuclei have a spin of 3/2 or higher, in which case quadrupolar terms are present, the majority of existing theoretical treatments assume a nuclear spin1/2 bath. In this work, we present a comprehensive theoretical framework of a driven electron spin coupled to a nuclear spin3/2 bath based on a meanfield approach, and we use it to study the effects of higher nuclear spin on dynamic nuclear polarization. 
Wednesday, March 4, 2020 3:18PM  3:30PM 
P17.00003: Longtime noise characteristics of an isotopicallyenriched silicon nuclear spin bath Matthew D Grace, Wayne M Witzel

Wednesday, March 4, 2020 3:30PM  3:42PM 
P17.00004: A silicon quantumdotcoupled nuclear spin qubit Bas Hensen, Wister Wei Huang, ChihHwan Yang, Kok Wai Chan, Jun Yoneda, Tuomo I Tanttu, Fay E. Hudson, Arne Laucht, Kohei M Itoh, Thaddeus D Ladd, Andrea Morello, Andrew Steven Dzurak Single nuclear spins in the solid state have long been envisaged as a platform for quantum computing. However, establishing longrange interactions between multiple dopants or defects is challenging. Conversely, in lithographicallydefined quantum dots, tunable interdot electron tunneling allows direct coupling of electron spinbased qubits in neighboring dots. Moreover, compatibility with semiconductor fabrication techniques provides a compelling route to scaling. Unfortunately, hyperfine interactions are typically too weak to address single nuclei. In this presentation, we report that for electrons in silicon metaloxidesemiconductor quantum dots the hyperfine interaction is sufficient to initialize, readout and control single silicon29 nuclear spins, yielding a combination of the long coherence times of nuclear spins with the flexibility and scalability of quantum dot systems. We demonstrate that the nuclear and electron spins can be entangled and that they both retain their coherence while moving the electron between quantum dots, paving the way to long range nuclearnuclear entanglement via electron shuttling. Our results establish nuclear spins in quantum dots as a powerful new resource for quantum processing [1]. 
Wednesday, March 4, 2020 3:42PM  3:54PM 
P17.00005: Engineering electrical control of single donor flipflop qubits for universal quantum computations Irene Fernández de Fuentes, Tim Botzem, Rostyslav Savytskyy, Stefanie Tenberg, Vivien Schmitt, Guilherme Tosi, Fay E. Hudson, Kohei M Itoh, David Norman Jamieson, Andrew Steven Dzurak, Andrea Morello The "flipflop" qubit is composed of the ↑↓ / ↓↑ states of the electron and nucleus spin of an implanted ^{31}P atom [1] in Si. It enables fast 1qubit gates through the electrical modulation of the hyperfine interaction, achieved by hybridizing the orbital states of the donor electron with a quantum dot at the Si/SiO_{2} interface. Biasing the electron wavefunction towards the interface creates a large electric dipole allowing for long distance coupling between donors, which mediates 2qubit logic gates. Coherent control of the flipflop states of an ^{123}Sb donor has been demonstrated, in a nonoptimized device. Here we present the progress in developing a CMOS compatible nanostructure, designed to enable accurate electric control of the hyperfine interaction (for coherent driving), and tunability on the coupling to charge reservoirs (for state readout). We report gated control of electron tunnel times of interface dots to a nearby readout quantum dot by nearly two orders of magnitude. We further investigate the effects of our highfrequency electrical antenna on the coherent control of both electron and nuclear spins. 
Wednesday, March 4, 2020 3:54PM  4:06PM 
P17.00006: Coherent electrical control of a single highspin nucleus in silicon Mark Johnson, Serwan Asaad, Vincent Mourik, Benjamin Joecker, Andrew Baczewski, Hannes Roland Firgau, Mateusz T Madzik, Vivien Schmitt, Jarryd Pla, Fay E. Hudson, Kohei M Itoh, Jeffrey C McCallum, Andrew Steven Dzurak, Arne Laucht, Andrea Morello We report the discovery of Nuclear Electric Resonance (NER) in a single 123 Sb donor, implanted in a 
Wednesday, March 4, 2020 4:06PM  4:18PM 
P17.00007: Decoherence of Dipole Coupled FlipFlop Qubits John Truong, Xuedong Hu A recent proposal for a scalable donorbased quantum computer scheme promises excellent coherence properties, fast qubit couplings and insensitivity to donor placement. The suggested system consists of two different types of qubits per donor: a flipflop qubit consisting of the electron and nuclear spin states, and a charge qubit of the donor electron tunneling between the donor and an interface quantum dot. In this scheme, the qubits can be coupled to each other via the electric dipole interaction between their respective charge qubits. We study in detail this effective coupling, especially the effect of charge noise on twoqubit gates utilizing this coupling. We find that due to the proximity of the charge excited states to the flipflop logical states, the presence of charge noise greatly reduces the fidelity of twoqubit operations. We calculate the qubitnoise interaction strengths, and identify leakage from the qubit Hilbert space as the main culprit of the reduced gate fidelity. We also explore different bias conditions to mitigate this decoherence channel. 
Wednesday, March 4, 2020 4:18PM  4:30PM 
P17.00008: Full configuration interaction simulations of exchange coupled donors in silicon in an effective mass theory framework Benjamin Joecker, Andrew D. Baczewski, John K Gamble, Jarryd Pla, Andrea Morello Several proposals for multiqubit gates with donor spin qubit in silicon rely on the exchange interaction, using either weak exchange and microwave pulses [1], or strong tunable exchange [2]. Designing the optimal devices to embody these control strategies requires accurate models of the dependence of the exchange interaction on lattice placement, orientations, and electric fields. Here, we use a full configuration interaction method within an established multivalley effective mass theory framework [3] to model the twoelectron wavefunction for different donor configurations. In particular, we investigate the exchange interaction and valley population along different lattice orientations, and the tunability of exchange with external electric fields. 
Wednesday, March 4, 2020 4:30PM  4:42PM 
P17.00009: Simultaneous Comparison of Coulomb Blockade Linewidths of P Donorbased and MOSbased Si Quantum Dots Yanxue Hong, Aruna N Ramanayaka, Michael David Stewart, Xiqiao Wang, Ranjit Kashid, Pradeep Namboodiri, richard Silver, Joshua Pomeroy In solidstate quantum computation, noise often presents a limitation for coherence or device integration. One indicator of the noise levels, the effective electron temperature (T_{eff}), must be as low as possible to enable highfidelity coherent measurements. High T_{eff} in the measurement may come from noise sources extrinsic to the device or from intrinsic noise in the device, which can be measured by the broadening of Coulomb blockade peaks. To study the extrinsic systematic noise origins and the intrinsic lattice couplings, here we report on the comparison of T_{eff} on two different quantum dot systems, P donorbased and MOSbased Si quantum dots simultaneously measured using the same measurement setup on the same platform. Tdependent and biasdependent conductance are measured in different cryogenic setups over temperatures ranging from 10 mK to 25 K. The T_{eff} is extracted using a theoretical model. By initially rearranging ground configuration and noise filtering, we have successfully reduced the T_{eff} in a dilution refrigerator with 10 mK base temperature to < 0.5 K. 
Wednesday, March 4, 2020 4:42PM  4:54PM 
P17.00010: Evaluating effective mass models of the phoshorous donor in silicon Luke Pendo, Xuedong Hu Evaluating effective mass models of a phosphorus donor in silicon is made difficult by conflation of mathematical and physical approximations. We propose a scheme to solve a class of effective mass models with high precision. We construct donor electron states using envelope functions expanded in freely extensible basis sets equipped with tunable parameters. With these states, we compute the expectation values of both the donor's energy as well as the energy variance. We variationally optimize the parameters of these basis states to find stationary points of the energy functional, with variance of the expectation energy used to evaluate the precision of our candidate eigenstates. In this manner, we can find exact energy eigenstates of the implied Hamiltonian of an effective mass model. 
Wednesday, March 4, 2020 4:54PM  5:06PM 
P17.00011: A twoqubit gate between phosphorus donor electrons in silicon Yu He, Samuel Keith Gorman, Daniel J Keith, Ludwik Kranz, Joris Gerhard Keizer, Michelle Y Simmons Electron spin qubits formed by atoms in silicon have large orbital energies and weak spinorbit coupling giving rise to isolated electron spin ground states with seconds long coherence times. The exchange interaction promises fast twoqubit gate operations between singlespin qubits. Until now, creating a tunable exchange interaction between two electrons bound to phosphorus atom qubits has not been possible. This reflects the challenges in knowing how far apart to place the atoms to turn on and off the exchange interaction, whilst aligning atomic circuitry for high fidelity independent read out of the spins. Here we report a ~800 ps √SWAP gate between phosphorus donor electron spin qubits in silicon with independent ~94 % fidelity single shot spin readout. By engineering qubit placement on the atomic scale, we provide a route to the realisation and efficient characterisation of multiqubit quantum circuits based on donor qubits in silicon. 
Wednesday, March 4, 2020 5:06PM  5:18PM 
P17.00012: Donorbound excitons in Cl doped ZnSe quantum wells Aziz Karasahin, Marvin Marco Jansen, Alexander Pawlis, Edo Waks Quantum information processing heavily depends on the ability to generate the high number of indistinguishable single photons and to interface them with longlived coherent spin states. Quantum dots as emerged as promising scalable solidstate platforms by offering bright photon emissions. However, epitaxially grown quantum dots are not immune to size variations and they suffer short coherence times due to interactions with host material nuclear spin bath. 
Wednesday, March 4, 2020 5:18PM  5:30PM 
P17.00013: Gfactor Anisotropy of a Single Electron in a GaAs Quantum Dot Simon Svab, Leon Camenzind, Liuqi Yu, Peter Stano, Jeramy D Zimmerman, Arthur C Gossard, Daniel Loss, Dominik Zumbuhl Spins in semiconductor quantum dots are among the leading candidates for quantum computing. To lift spin degeneracy, a large inplane magnetic field is applied. This has sizable effects on the confined electron, allowing the shape and orientation of the orbitals to be inferred in this way, see Camenzind et al. PRL112, 207701 (2019). 
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