Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D74: Quantum Computing with Donor Spins IFocus
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Sponsoring Units: DQI Chair: Patrick Harvey-Collard, IBM Research - Zurich Room: Room 403/404 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D74.00001: Silicon spin qubits with implanted single donor ions Invited Speaker: Danielle Holmes Single group-V donors in isotopically-enriched silicon (28Si) are strong qubit candidates due to their long spin coherence times [1], small footprints and compatibility with the microelectronics industry. The spin of both the donor electron and nucleus, our resources for storing quantum information, can be controlled and readout using surface nanoelectronics and coupled over a range of length scales. High spin nuclei, such as antimony (123Sb), provide exciting opportunities for storing more quantum information, all electrical control [2] and exploring quantum chaos [3]. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D74.00002: Understanding transport in dopant arrays in silicon Garnett W Bryant, Michal Gawelczyk, Michal Zielinski The recent development of precision phosphorus donor placement in silicon has stimulated the use of donor arrays for quantum simulation of the extended Hubbard and Su-Schrieffer Heeger models. Transport is used to probe the many-body states of these arrays. We employ exact diagonalization combined with non-equilibrium Green's functions to model transport through 3x3 dopant arrays in Si and extract information about the many-body states in the arrays. We characterize the many-body configurations that contribute to the current, determine current magnitudes for different channels, and visualize how the electron flow circumvents disturbances in the form of array randomness. We find that charge stability diagrams are dominated by current channels corresponding to transport along rows in the 3x3 array, as seen experimentally. This response is robust against effects of disorder. Even if a row is blocked by removal of a middle site, current can flow around the blockade. In addition, we model the time evolution of the many-body state of the array when a spin is injected from the source and extracted into the drain. This provides us with a picture of how spin and charge move through the array, establishing the many-body dynamics that could be seen by experiment. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D74.00003: Simulation of Parallel Gate Fidelities in 1D and 2D Arrays of Noisy Flip-Flop Qubits Marco De Michielis, Elena Ferraro The anti-parallel spin states of the nucleus and the bonded electron of a 31P atom located in a 28Si substrate form a good quantum system to define a qubit, the Flip-Flop Qubit (FFQ) [1]. One-qubit operations have been experimentally demonstrated in a FFQ this year [2] and two-qubit gates are foreseen to be generated by using the electric dipole-dipole interaction between a couple of FFQs [1]. This long-range dipole-dipole interaction can be exploited to relax the common device fabrication requirements on the lateral positioning of top metal electrodes from a range of few tens nm in quantum dot-based qubit arrays to one of few hundreds nm in FFQ arrays. Parallel gating, that’s the simultaneous application of gates on many qubits, is limited by unwanted inter-qubit interactions thus narrowing the quantum error correction (QEC) codes effectiveness to achieve the long-term goal of a fault-tolerant quantum computation. Parallel one-qubit and two-qubit gate fidelities are simulated in 1D [3] and 2D arrays when embedded in a realistic noisy environment. We analyze the parallel gate fidelity results obtained in different configurations of active/idle FFQs for some inter-qubit distances, exploring strategies to mitigate the unwanted interaction effects and to enhance the performances of selected QEC codes. [1] Tosi et al., Nat. Comm. 2017, 8450. [2] Savytskyy et al., arXiv:2202.04438. [3] Rei et al., Adv. Quantum Technol. 2100133 2022. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D74.00004: Spin-orbit interactions of two phosphorus donors in silicon Yu-Ling Hsueh, Daniel Keith, Yousun Chung, Samuel K Gorman, Ludwik Kranz, Serajum Monir, Zachary Kembrey, Joris G Keizer, Michelle Y Simmons, Rajib Rahman Understanding the form and strength of the spin-orbit interaction is important for spin qubit design. While strong spin-orbit couplings allow us to drive the electron spin qubit electrically, charge noise and phonon also couple to the electron spin and cause decoherence. We show in this work various spin-orbit terms are present depending on the separation direction of the two donors, giving rise to anisotropy in the electron spin relaxation time T1 in a 2P donor dot qubit. Charge noise causes the electron spin to relax through spin-orbit terms whilst the resulting spin relaxation, together with hyperfine mediated phonon relaxation, explain the measured anisotropy. We show how we can extend the T1 times ∼ 40 s by minimising the effect of spin-orbit and charge noise and/or by using low magnetic fields (B = 0.75 T) and utilising ramped measurement techniques [1]. Finally, by analysing and modelling the charge noise in the device and obtaining the noise amplitude, we extract the spin-orbit strength which gives the corresponding T1 times. We find that the HEB spin-orbit strength of a 2P donor dot is similar to the HEB spin-orbit strength of a 1P donor dot [2]. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D74.00005: Stark effect in phosphorus donor dots: electrical control of electron and nuclear spins Md Serajum Monir, Yuling Hsueh, Michael T Jones, Pascal Macha, Jonathan Reiner, Samuel K Gorman, Michelle Y Simmons, Rajib Rahman
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Monday, March 6, 2023 4:24PM - 4:36PM |
D74.00006: Universal nuclear two-qubit logic operations in an exchange-coupled donor system Holly G Stemp, Serwan Asaad, Mark A Johnson, Kohei M Itoh, Alexander M Jakob, Brett C Johnson, David N Jamieson, Fay E Hudson, Andrew S Dzurak, Arne Laucht, Andrea Morello Scalable quantum processors require high-fidelity universal quantum logic operations, in a manufacturable physical platform, along with the capacity to couple multiple qubits together over a variable range of length scales. Nuclear spins of ion-implanted donors in silicon have demonstrated record-breaking coherence times [1], along with high fidelity (> 99%), universal 1 and 2-qubit operations [2][3], approaching the fidelity required to perform fault-tolerant quantum computation. Geometric nuclear 2-qubit controlled-Z (CZ) gates have been performed by using a single electron whose resonance frequency is conditional on the state of both nuclei [3]. This, however, requires very close spacing between the nuclei. Here we demonstrate a CZ gate between the nuclei of two widely-separate atoms, each possessing their own bound electron. The two electrons, in turn, are coupled by a weak exchange interaction J = 12 MHz, corresponding to an estimated inter-donor distance of 24 nm. Through this two-electron interaction, we are able to couple and entangle nuclei over a much larger distance than previously demonstrated. We benchmark the fidelity of these 1 and 2-qubit nuclear operations using gate set tomography (GST). Combined with the ability to perform electron 2-qubit gates between two exchange-coupled electrons [4], this work completes the toolbox for constructing a scalable spin-based quantum processor in silicon. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D74.00007: An open source software package to compare and extend effective mass models of the phosphorus donor in silicon Luke M Pendo, Xuedong Hu Evaluating effective mass models of an isolated phosphorus donor in silicon requires disentangling various sources of error. In an effort to suppress the error resulting from state approximation, we have put together an open source software package to explore the limits of the effective mass model. In this package, we construct states using envelope functions expanded in freely extensible basis sets equipped with tunable parameters. Additionally, a full consideration of the effect of symmetry is applied to this basis set. This robust basis set allows us to compute arbitrarily precise approximate eigenstates of the effective mass Hamiltonian as confirmed by near zero values of the energy variance. We can, in principle, closely approximate the exact electronic structure of the donor in the context of effective mass for a broad class of model potentials, which in turn allows us to evaluate and compare extant and new effective potential models. In this talk, we examine models of the donor atom's Coulomb potential considering the effects of a dielectric constant with dynamic response. Further, we go beyond the Coulomb potential and present phenomenological psuedopotentials to include exchange and correlation effects from the donor's valence electrons. Finally, we include symmetry breaking perturbations, in particular the effect of an external electric field upon the donor electron. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D74.00008: Universal SU(8) control of a high-spin nucleus in silicon Xi Yu, Benjamin Wilhelm, Pragati Gupta, Arjen Vaartjes, Daniel Schwienbacher, Barry C Sanders, Andrea Morello We have developed a global rotation control scheme for controlling the nucleus of the high-spin 123Sb donor (I=7/2) implanted in silicon – an appealing platform for realization of quantum processors [1] and for exploration of quantum chaos [2]. As opposed to individually addressing the transition between pairs of energy levels (‘ladder climbing’), in this scheme a multi-frequency control pulse drives all the NMR frequencies simultaneously, allowing one to implement global rotations defined in I=7/2 Bloch sphere, i.e. SU(8) rotation operators. In practice, an FPGA-based AWG generates multichromatic RF pulses and handles a ‘generalized rotating frame’ [3] by keeping track of multiple phases at each of the nuclear resonance frequencies. Multiple future experimental endeavours can benefit from implementing global rotations. For example, it allows to more efficiently initialize arbitrary quantum states compared to the conventional 'ladder-climbing' protocol. Special states of interests are spin coherent states in arbitrary directions, Schrödinger’s cat states, and logical qubits encoding in high-spin nuclei [4]. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D74.00009: Extending the low-frequency limit of qubit noise spectroscopy beyond the inverse dephasing time Benjamin Wilhelm, Xi Yu, Yuanlong Wang, Gerardo Paz Silva, Tim Botzem, Andrea Morello Noise-aware quantum control strategies have shown great promise to reach gate fidelities necessary for operating fault-tolerant quantum computers. These protocols rely on detailed knowledge of the noise, which requires an accurate, full bandwidth characterisation. Conventional noise spectroscopy protocols [1] fail to provide information about the noise spectrum below the inverse of the T2 coherence time. This limitation is particularly severe in most solid-state quantum systems, where 1/f noise dominates. Here, we demonstrate a novel spectroscopy protocol that circumvents this limitation by employing control sequences which allow moving the sampling regime to lower frequency regions. We apply this method to 31P donor qubits in silicon [2] and estimate the basic properties of the low-frequency noise by applying a Bayesian reconstruction algorithm. We verify our approach by detecting noise that we intentionally introduce to the system. With the information gained from this method we expect to design noise-aware quantum gates that further increase gate fidelities beyond fault-tolerant thresholds. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D74.00010: Quantum Simulation of Dynamical Lattices using Electrons in Silicon Dopant Arrays Ali Rad, Michael J Gullans, Alexander Schuckert, Eleanor Crane, Mohammad Hafezi, Gautam Nambiar, Zohreh Davoudi, Richard M Silver
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Monday, March 6, 2023 5:24PM - 5:36PM |
D74.00011: Optimisation of electron spin qubits in electrically driven multi-donor quantum dots Abhikbarta Sarkar, Joel Hochstetter, Allen Kha, Xuedong Hu, Michelle Y Simmons, Rajib Rahman, Dimitrie Culcer Multi-donor quantum dots have been at the forefront of recent progress in Si-based quantum computation. Among them, 2P:1P spin qubits have a built-in dipole moment, making them ideal for electron dipole spin resonance (EDSR) using the donor hyperfine interaction. The development of such all-electrical spin qubits requires a full understanding of their EDSR and coherence properties, in which multi-donor dot qubits are expensive to model computationally due to the multi-valley nature of their ground state. Here we examine the impact of qubit geometry and nearby charge defects on the electrical operation and coherence of a 2P:1P electron spin qubit. We report fast EDSR, with Tπ ∼ 10 - 50 nanoseconds and a Rabi ratio (T1/Tπ) ∼ 106. The fastest EDSR time Tπ occurs when the 2P:1P axis is ? [111], while the best Rabi ratio occurs when it is ? [100]. Sensitivity to random telegraph noise due to nearby charge defects depends strongly on the location of the nearby defects with respect to the qubit. The qubit is robust against 1/f noise provided it is operated away from the charge anti-crossing. Entanglement via exchange is several orders of magnitude faster than dipole-dipole coupling. These findings pave the way towards fast, low-power, coherent and scalable donor dot-based quantum computing. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D74.00012: Low Thermal Budget PMOS for Qualifying the Semiconductor Environment of STM-placed Donor Qubits Christopher R Allemang, Deanna M Campbell, Jeffrey A Ivie, Tzu-Ming Lu, Shashank Misra Understanding and control of the solid-state environment of semiconductor spin qubits is critical for their performance. Donor-based qubits are appealing components of a semiconductor spin-based quantum computer because of their long coherence times. Moreover, donor-donor exchange coupling can be controlled precisely with atomically precise placement of donors using scanning tunneling microscopy (STM). However, unlike gate-defined quantum dots, where capacitor and Hall bar measurements have provided a useful proxy for the qubit environment, it has been difficult to evaluate the environment of STM-placed donor qubits using anything other than time-consuming qubit measurements. Here, we describe the fabrication and measurement of low thermal budget p-type metal oxide semiconductor (PMOS) transistors for quick evaluation of the STM-placed donor qubit environment. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D74.00013: High fidelity coherent magnetic and electric control of a single spin-7/2 donor atom in Silicon Daniel Schwienbacher, Irene Fernández de Fuentes, Arjen Vaartjes, Tim Botzem, Benjamin Joecker, Fay E Hudson, Alexander M Jakob, Kohei M Itoh, Andrew S Dzurak, David N Jamieson, Andrea Morello High-spin nuclei, such as the spin-7/2 system 123Sb, provide an optimal platform for advanced spin architectures [1]. They can be used to investigate fundamental physic as well as being the base of future quantum computing efforts. In addition to the standard magnetic field control, nuclear spins with I>1/2 exhibit an electric quadrupole moment that offers a way to control the nuclear spins using nuclear electric resonance. In this talk, we show full coherent magnetic and electric control of the 16-dimensional Hilbert space of a 123Sb donor. On the ionized nuclear spin, we demonstrate one-qubit gate fidelities of 99.8% using Gate Set Tomography. Measuring the state-dependent Ramsey coherence times of the donor nucleus allows us to separate electric and magnetic noise sources. These results lay the foundations for exploiting high-spin donor nuclei in experiments on logical qubit encoding [2], quantum sensing [3] and high-dimensional quantum information processing. [1] S. Asaad et al., Nature 579, 205–209 (2020)
[2] J. Gross, Phys. Rev. Lett. 127, 010504 (2021) [3] T. Chalopin et al., Nature Comm. 9, 4955 (2018) |
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