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 2-qubit logic gates with implanted donors in silicon Invited Speaker: Andrea Morello Ion-implanted 31P donors in silicon have attained 1-qubit gate fidelities >99.9% [1]. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P17.00002: Driven dynamics of an electron coupled to spin-3/2 nuclei in quantum dots Arian Vezvaee, Girish Sharma, Sophia Economou, Edwin Barnes The problem of hyperfine interaction between a confined electron in a self-assembled 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 spin-1/2 bath. In this work, we present a comprehensive theoretical framework of a driven electron spin coupled to a nuclear spin-3/2 bath based on a mean-field 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: Long-time noise characteristics of an isotopically-enriched silicon nuclear spin bath Matthew D Grace, Wayne M Witzel
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Wednesday, March 4, 2020 3:30PM - 3:42PM |
P17.00004: A silicon quantum-dot-coupled nuclear spin qubit Bas Hensen, Wister Wei Huang, Chih-Hwan 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 long-range interactions between multiple dopants or defects is challenging. Conversely, in lithographically-defined quantum dots, tunable interdot electron tunneling allows direct coupling of electron spin-based 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 metal-oxide-semiconductor quantum dots the hyperfine interaction is sufficient to initialize, read-out and control single silicon-29 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 nuclear-nuclear 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 flip-flop 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 "flip-flop" qubit is composed of the ↑↓ / ↓↑ states of the electron and nucleus spin of an implanted 31P atom [1] in Si. It enables fast 1-qubit 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/SiO2 interface. Biasing the electron wavefunction towards the interface creates a large electric dipole allowing for long distance coupling between donors, which mediates 2-qubit logic gates. Coherent control of the flip-flop states of an 123Sb donor has been demonstrated, in a non-optimized 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 read-out quantum dot by nearly two orders of magnitude. We further investigate the effects of our high-frequency 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 high-spin 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 Flip-Flop Qubits John Truong, Xuedong Hu A recent proposal for a scalable donor-based 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 flip-flop 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 two-qubit gates utilizing this coupling. We find that due to the proximity of the charge excited states to the flip-flop logical states, the presence of charge noise greatly reduces the fidelity of two-qubit operations. We calculate the qubit-noise 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 multi-qubit 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 two-electron 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 Donor-based and MOS-based Si Quantum Dots Yanxue Hong, Aruna N Ramanayaka, Michael David Stewart, Xiqiao Wang, Ranjit Kashid, Pradeep Namboodiri, richard Silver, Joshua Pomeroy In solid-state quantum computation, noise often presents a limitation for coherence or device integration. One indicator of the noise levels, the effective electron temperature (Teff), must be as low as possible to enable high-fidelity coherent measurements. High Teff 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 Teff on two different quantum dot systems, P donor-based and MOS-based Si quantum dots simultaneously measured using the same measurement setup on the same platform. T-dependent and bias-dependent conductance are measured in different cryogenic setups over temperatures ranging from 10 mK to 25 K. The Teff is extracted using a theoretical model. By initially rearranging ground configuration and noise filtering, we have successfully reduced the Teff 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 two-qubit 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 spin-orbit coupling giving rise to isolated electron spin ground states with seconds long coherence times. The exchange interaction promises fast two-qubit gate operations between single-spin 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 read-out. By engineering qubit placement on the atomic scale, we provide a route to the realisation and efficient characterisation of multi-qubit quantum circuits based on donor qubits in silicon. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P17.00012: Donor-bound 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 long-lived coherent spin states. Quantum dots as emerged as promising scalable solid-state 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: G-factor 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 in-plane 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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