Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K37: Quantum Computing with Donor Spins IIFocus Recordings Available
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Sponsoring Units: DQI Chair: Berk Kovos, UChicago Room: McCormick Place W-194B |
Tuesday, March 15, 2022 3:00PM - 3:12PM |
K37.00001: Radio Frequency Reflectometry on Si:P Quantum Devices Joseph B Fox, ranjit V Kashid, Xiqiao Wang, Pradeep Namboodiri, Jonathan Wyrick, Richard M Silver, Neil Zimmerman Si:P monolayer quantum devices fabricated using STM based hydrogen lithography are a strong candidate for spin-based quantum computing. Scaling these devices to larger numbers of spin-based donor qubits is impeded by the amount of physical space required for the readout sensors. Radio frequency reflectometry addresses these issues by minimizing the physical footprint of the sensor, while potentially reducing the sensitivity to noise as the measurement can operate at a higher frequency than DC readout. This presentation will discuss our progress in developing a gate-based and ohmic RF reflectometry technique that is capable of single shot-readout and compare reflectometry results with typical DC based measurements. We will describe our optimization for this technique and the use of impedance matching in order to increase measurement sensitivity. |
Tuesday, March 15, 2022 3:12PM - 3:24PM |
K37.00002: Ensemble spin relaxation studies of shallow donor qubits in ZnO Vasileios Niaouris, Xiayu Linpeng, Mikhail V Durnev, Maria Viitaniemi, Christian Zimmermann, Aswin Vishnuradhan, Y. Kozuka, Masashi Kawasaki, Kai-Mei C Fu Neutral shallow donor qubits in ZnO, such as Al, Ga, and In substituting for Zn, are a promising new spin-qubit platform for quantum technologies such as hybrid quantum networks [1]. In previous work, we have demonstrated optical spin initialization, spin relaxation times (T1) of 140 μs, spin-echo coherence times (T2) of 50 μs and narrow inhomogeneously broadened linewidths of ≈25 GHz [2]. Here, we will present an experimental and theoretical study of the longitudinal spin relaxation of electrons bound to neutral shallow Ga donors. Experimentally, an inverse power dependence on magnetic field is observed, with T1 ranging from 1 ms to 480 ms over 7 T to 1.75 T. Experimental results are compared to a theoretical model which suggests that the spin relaxation is mediated by the phonon emission/absorption in the presence of spin-orbit coupling (admixture mechanism). We additionally find an effect of the excitation energy on T1. The experimental data suggest additional mechanisms that (a) soften the magnetic field dependence at high fields and (b) speed up the relaxation process with varying donor densities. |
Tuesday, March 15, 2022 3:24PM - 3:36PM |
K37.00003: Coherent Spin Preparation of Indium Donor Qubits in Single ZnO Nanowires Christian Zimmermann, Maria Viitaniemi, Vasilis Niaouris, Sam D'Ambrosia, Xingyi Wang, E. Senthil Kumar, Faezeh Mohammadbeigi, Simon P. Watkins, Kai-Mei C Fu Neutral shallow donors in ZnO, such as impurities substituting on a Zn site, are promising candidates for photon-mediated quantum technologies. Here, we will focus on the indium donor in isolated ZnO nanowires. Compared to bulk ZnO, isolated nanowires offer a promising avenue to isolate few/single donors. Moreover, nanostructures can be used for photonic device integration. We show that favorable donor-bound exciton optical and electron spin properties are retained in isolated ZnO nanowires. The inhomogeneous optical linewidth of small ensembles of indium donors in single nanowires (60 GHz) is within a factor of 2 of what is found for single-crystalline bulk ZnO. In isolated ZnO nanowires, spin initialization via optical pumping is demonstrated and coherent population trapping is observed. The two-photon absorption width approaches the theoretical limit expected due to the strong hyperfine interaction between the indium nuclear spin and the donor-bound electron. Notably, the strong hyperfine interaction observed for indium donors with a nuclear spin of 9/2 paves the way for qubit registers in ZnO with potential applications in quantum memories. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K37.00004: Transport and Tunneling in Atomic-scale Acceptor-based Devices in Silicon Sungha Baek, Kevin J Dwyer, James R Williams, Robert E Butera Ultradoped silicon provides a novel frontier for the exploration of electronic transport in a disordered potential with extremely high carrier concentrations (> 1014 cm-2). Atomic-precision advanced manufacturing (APAM) techniques associated with scanning tunneling microscopy (STM)-based lithography can be used to confine the dopants to quasi-2D regions of silicon having dimensions from microns to angstroms. This plays an essential role in building dopant-based nanoelectronic devices for single dopant atom qubit measurement and control. This process has recently been extended to include acceptor doping with B. Here, we present the details of fabrication and measurement of gated Si∶B wires and single hole transistors (SHTs) to provide insight into transport and tunneling in these planar, atomic-scale devices at low temperatures. Such a detailed understanding provides the pathway towards engineering and realization of single B atom-based devices in silicon. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K37.00005: Engineering hyperfine Stark shifts for addressable high-speed gates in donor molecules in silicon Michael T Jones, Yu-ling Hsueh, Felix N Krauth, Pacal Macha, Serajum Monir, Angus Worrall, Yousun Chung, Joris G Keizer, Matthew G House, Rajib Rahman, Michelle Y Simmons Electron and nuclear spin qubits on single donor atoms in silicon have demonstrated long coherence times with high fidelities. Recent results have demonstrated the ability to form fast (0.8ns) two qubit gates using donor molecules in silicon. Scalable quantum computer architectures require the ability to combine fast single and two qubit gates with individual qubit addressability across an array to minimise errors on neighbouring qubits. Single donor qubits require a large ~30MHz/MVm-1 hyperfine Stark shift of the qubit resonance frequency to uniquely address identical single donor nuclear spins. Previous results on single phosphorus donor spins have measured a hyperfine Stark coefficient of 0.34MHz/MVm-1, well below that identified in the Kane architecture thereby limiting the speed of addressable quantum gates. By comparing experimental results of donor molecules in silicon with tight binding simulations of 2P molecules we demonstrate atomic engineering of donor qubits in silicon to control a large range of hyperfine Stark coefficients (up to 72MHz/MVm-1). We discuss how these results can be extended to achieving high speed gates using electrically driven spin resonance control. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K37.00006: Beating the thermal limit of qubit initialization with a Bayesian 'Maxwell's demon' Mark A Johnson, Mateusz T Madzik, Fay E Hudson, Kohei M Itoh, Alexander M Jacob, David N Jamieson, Andrew S Dzurak, Andrea Morello Fault-tolerant quantum computing requires initializing the quantum register in a well-defined fiducial state. In solid-state systems, this is typically achieved through thermalization to a cold reservoir, such that the initialization fidelity is fundamentally limited by temperature. Here we present a method of preparing a fiducial quantum state that beats the thermal limit. It is based on real-time monitoring of the qubit through a negative-result measurement -- the equivalent of a `Maxwell's demon' that only triggers the experiment upon the appearance of a very cold qubit. We experimentally apply it to initialize an electron spin qubit in silicon, achieving a ground-state initialization fidelity of 98.9(4)%, a ≈19% improvement over the intrinsic fidelity of the system. A fidelity approaching 99.9% could be achieved with realistic improvements in the bandwidth of the amplifier chain or by slowing down the rate of electron tunneling from the reservoir. We use a nuclear spin ancilla, measured in quantum nondemolition mode, to prove the value of the electron initialization fidelity far beyond the intrinsic fidelity of the electron readout. The quantitative analysis of the initialization fidelity reveals that a simple picture of spin-dependent electron tunneling does not correctly describe the data. Our digital `Maxwell's demon' can be applied to a wide range of quantum systems, with minimal demands on control and detection hardware. |
Tuesday, March 15, 2022 4:12PM - 4:48PM |
K37.00007: Acceptor-based hole spin qubits in silicon Invited Speaker: Joseph Salfi Spins qubits in silicon are appealing to build quantum computers due to their small area, long coherence times, and compatibility with industrial manufacturing processes. Spin-orbit coupling is appealing to improve the scalability of such systems, enabling simple, long-distance schemes for single-qubit and multi-qubit operations, using microwave photons, phonons, or capacitive coupling [1,2]. A fundamental question is whether qubit coherence time must be sacrificed for qubits with strong spin-orbit coupling, as typically observed over the last 10 to 15 years. Here we present experimental results showing that this is emphatically not the case. We demonstrate 10 millisecond spin coherence times for holes bound to acceptor atoms in isotope purified silicon [3], where spin-orbit coupling yields quantized total angular momentum $J=3/2$, rivaling electron spin qubits, and $10^4$ to $10^5$ times longer than previous spin-orbit qubits in silicon. The key ingredient is to suppress the longitudinal electric dipole by controlling the energy separation of the $|m_J|=1/2$ and $|m_J|=3/2$ doublets, using strain. Recent theory shows that this holds not only for impurities [3] but also quantum dots [4] and for group IV materials, not just Si. These results suggest group IV hole spin qubits as an ideal platform for ultra-fast, highly coherent scalable quantum computing. [1] Ruskov and Tahan, Phys. Rev. B, 88, 064308, 2013. [2] Tosi et al, Nature Communications 8, 450, 2017. [3] Kobayashi, Salfi et al, Nature Materials 20 38 2021. [4] Wang, Marcellina et al, npj Quantum Information 7, 1, 2021. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K37.00008: Minimising spin relaxation in donor atom qubits in silicon Yu-Ling Hsueh, Daniel Keith, Serajum Monir, Yousun Chung, Samuel K Gorman, Michelle Y Simmons, Rajib Rahman Donor electron spin qubits hosted within nanoscale devices have demonstrated seconds-long relaxation times [1-4] at magnetic fields suitable for the operation of spin qubits in silicon of B = 1.5 T. The relaxation rates of these qubits have been shown at milliKelvin temperatures to be mediated by spin-orbit coupling with a B5 dependency on magnetic field for B > 3T with a transition to a B3 dependency at magnetic fields below (B ≤ 3T) particularly in multi-donor quantum dot qubits [4]. We identify the relaxation mechanisms that give rise to this saturation at low field and show how, by atomically engineering the device we can minimise this effect extending T1 to ∼200 seconds at B = 1.5 T. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K37.00009: Multimode Storage of Quantum Microwave Fields in Electron Spins over 100 milliseconds Vishal Ranjan, James O'Sullivan, Emanuele Albertinale, Bartolo Albanese, Thierry Chaneliere, Thomas Schenkel, Denis Vion, Daniel Esteve, Emmanuel Flurin, John Morton, Patrice Bertet We report long coherence times (up to 300 ms) for near-surface bismuth donor electron spins in silicon coupled to a superconducting microresonator, biased at a clock transition [G. Wolfowicz, Nat nano, 8, 561 (2013)]. This enables us to demonstrate the partial absorption of a train of weak microwave fields in the spin ensemble, their storage for 100 ms, and their retrieval, using a Hahn-echo-like protocol. We also discuss the phase coherence and quantum statistics of the retrieved states. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K37.00010: Defect-assisted high activation yields of bismuth donors in silicon Youcef A Bioud, Sjoerd Roorda, Eva Dupont-Ferrier Bismuth donors in silicon are extremely promising candidates for applications within quantum technologies [1]. However, there are physical and technological challenges, which need to be overcome in order to achieve their potential [2]. This work considers the effect of destroying the crystalline structure of silicon and annealing conditions on the activation of Bi donors implanted to a depth of 20 nm. Secondary Ion Mass Spectrometry (SIMS) and Hall measurements were performed in order to calculate the proportion of the dopant, which was electrically active. The electrical activation yield (EAY) of implanted donors decreases with annealing temperature and achieves 60% for crystalline Si and 90% for preamorphized Si at a low thermal budget. Micro-Raman and XPS measurements show a strong correlation between annealing temperature and silicon recrystallization, which is more complex than solely considering the effect of EAY. These results demonstrate the significance in careful selection of optimal implantation and activation strategies when considering the fabrication of quantum devices based on active bismuth impurity states in silicon. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K37.00011: Coherent quantum control of a single 123Sb atom in silicon. Irene Fernández de Fuentes, Tim Botzem, Fay E Hudson, Kohei M Itoh, Andrew S Dzurak, Andrea Morello High-spin nuclei – such as the spin-7/2 from 123Sb - implanted in a silicon nano-device provide a compelling platform for advancing donor spin quantum architectures as well as investigating fundamental physics. The quadrupolar interaction in heavy group-V donors offers a natural way to control nuclear spins using electric fields, which are easier to confine in a nanoscale device, as opposed to magnetic fields. Past work by Asaad et al., [1], showed that the nucleus of a single 123Sb atom can be integrated into a nanoelectronic device and be used to encode quantum information through Nuclear Electric Resonance. In this work, we demonstrate coherent magnetic control on a single implanted atom of 123Sb in a semiconductor nanostructure, which had not been realized before. The magnetic antenna allows us to reconstruct the full NMR and ESR spectrum, characterize the quadrupolar interaction and investigate the performance and sources of noise for both magnetic and electric coherent control. Thanks to their large Hilbert space, high-spin nuclei set the pathway for protected qubit encoding [2] and all-electrical control in single-atom semiconductor devices. |
Tuesday, March 15, 2022 5:36PM - 5:48PM |
K37.00012: Engineering local strain for single-atom nuclear acoustic resonance in silicon Benjamin Joecker, Laura A O'Neill, Andrew D Baczewski, Andrea Morello Mechanical strain plays a key role in the physics and operation of nanoscale semiconductor systems, including quantum dots and single-dopant devices. Here we describe the design of a nanoelectronic device where a single nuclear spin is coherently controlled via nuclear acoustic resonance (NAR) through the local application of dynamical strain. The strain drives spin transitions by modulating the nuclear quadrupole interaction. We adopt an AlN piezoelectric actuator compatible with standard silicon metal-oxide-semiconductor processing, and optimize the device layout to maximize the NAR drive. We predict NAR Rabi frequencies of order 200Hz for a single 123Sb nucleus in a wide region of the device. Spin transitions driven directly by electric fields are suppressed in the center of the device, allowing the observation of pure NAR. Using electric field gradient-elastic tensors calculated by density-functional theory, we extend our predictions to other high-spin group-V donors in silicon, and to the isoelectronic 73Ge atom. |
Tuesday, March 15, 2022 5:48PM - 6:00PM |
K37.00013: Donor qubit in a transition metal dichalcogenide monolayer Arnau Sala, Sabyasachi Tiwari, William G. Vandenberghe, Bart Soree In the past few years, lots of efforts have been put into studying the possibility of implementing semiconductor spin qubits using transition metal dichalcogenides (TMD). Properties such as a large band gap, a valley-spin hybridization, and a large spin-orbit interaction, together with its low dimensionality and the possibility of synthesizing large sheets of these materials, make them an interesting choice for a platform for quantum computation. Motivated also by the long coherence times observed in phosphorous donors in silicon, we theoretically investigate the feasibility of implementing a donor spin qubit in a monolayer TMD. We consider a device consisting of a Mn donor in a MoS2 monolayer. We model the TMD-donor system using a combination of first principles density functional theory (DFT) calculations and localized Wannier functions. We next propose a discrete Hubbard-like model to describe the full dynamics of the TMD-donor qubit which is parameterized using the first-principles calculations. We demonstrate full control of the qubit via external electric fields, where we take advantage of a spin-orbit coupling, and discuss the possibility of coupling this qubit to nearby quantum dots or other donor qubits. |
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