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 C29: Semiconductor Qubits IFocus Live

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Sponsoring Units: DQI Chair: Tristan Meunier 
Monday, March 15, 2021 3:00PM  3:12PM Live 
C29.00001: Lowfrequency spectroscopy for quantum multilevel systems Artem Ryzhov, Sergey Shevchenko, Franco Nori A periodically driven quantum system with avoidedlevel crossing experiences both nonadiabatic transitions and wavefunction phase changes. These result in coherent interference fringes in the system’s occupation probabilities. For qubits, with repelling energy levels, such interference, named after LandauZenerStückelbergMajorana, displays arcshaped resonance lines. In the case of a multilevel system with an avoidedlevel crossing of the two lower levels, we demonstrate that the shape of the resonances can change from convex arcs to concave heartshaped and harpshaped resonance lines. Indeed, the whole energy spectrum determines the shape of such resonance fringes and this also provides insight into the slowfrequency system spectroscopy. As a particular example, we consider this for valleyorbit silicon quantum dots, which are important for the emerging field of valleytronics. 
Monday, March 15, 2021 3:12PM  3:24PM Live 
C29.00002: Theory of valley splitting and valleyinduced relaxation of a single silicon spin qubit in the presence of interface disorder Amin Hosseinkhani, Guido Burkard In silicon spin qubits, the qubit must be tuned away from the spinvalley hotspot to prevent fast qubit relaxation. We study in detail how the valley splitting depends on the electric and magnetic fields for both ideal and disordered Si/SiGe interfaces. Importantly, our modeling makes it possible to analyze the effect of arbitrary configurations of interface steps. We find, depending on where the interface steps are located, the magnetic field can increase or suppress the valley splitting. Moreover, the valley splitting can scale linearly or, in the presence of interface steps, nonlinearly with the electric field [1]. 
Monday, March 15, 2021 3:24PM  3:36PM Live 
C29.00003: Protecting Quantum Information in Quantum Dot Spin Chains by Driving Exchange Interactions Periodically John Van Dyke, Yadav Kandel, Haifeng Qiao, John Nichol, Sophia Economou, Edwin Barnes We analyze a new type of discrete time crystalline behavior that is obtained by periodically driving exchange interactions in a Heisenberg spin chain. This behavior is shown to benefit the protection and manipulation of multispin quantum states. We use these ideas to further construct a timecrystalinspired CZ gate between singlettriplet qubits with high fidelity. Our results indicate that periodically driving exchange couplings can enhance the performance of quantum dot spin systems for quantum information applications. 
Monday, March 15, 2021 3:36PM  3:48PM Live 
C29.00004: Impact of valley phases on exchange interaction in silicon double quantum dots Bilal Tariq, Xuedong Hu The presence of degenerate conduction band valleys and how they are mixed by interfaces play critical roles in determining electron interaction and spectrum in a silicon nanostructure. Here we investigate how the valley phases affect the exchange interaction in a symmetric twoelectron silicon double quantum dot. Within the HeitlerLondon approximation limited to the ground orbital states, exchange splitting is suppressed at a finite value of valley phase difference between the two dots and reaches its minimum value (~0) when the phase difference is π. Such a suppression can be explained using the Hubbard model and the absence of difference in double occupation. The contributions of the higher orbital states thus play a vital role in determining the value of the exchange energy in general. 
Monday, March 15, 2021 3:48PM  4:00PM Live 
C29.00005: Silicon quantum dot devices for scalable quantum computing Simon Geyer, Leon Camenzind, Lukas Czornomaz, Veeresh Deshpande, Andreas Fuhrer, Richard J. Warburton, Dominik Zumbuhl, Andreas Kuhlmann Silicon (Si) quantum dot (QD) spin qubits have great potential for application in largescale quantum circuits as they share many similarities with classical transistors that represent the prototypical example for scalable electronic platforms. However, for QD formation and control, additional gates are required that add to device complexity and thus hinder upscaling. Here, we meet this challenge by demonstrating the scalable integration of a multilayergatestack in Si QD devices using selfalignment, which allows for ultrasmall gate lengths and intrinsically perfect layertolayer alignment [Geyer et al., arXiv:2007.15400 (2020)]. We study hole transport through a double QD and observe Pauli spin blockade (PSB). Application of a small magnetic field leads to lifting of PSB and reveals the presence of spinorbit interaction. From the magnitude of a singlettriplet anticrossing at high magnetic field we estimate a spinorbit energy of 37µeV, which corresponds to a spinorbit length of just 48nm. This work paves the way for scalable spinbased quantum circuits with fast, allelectrical qubit control and operation temperatures above 1K. 
Monday, March 15, 2021 4:00PM  4:12PM Live 
C29.00006: Spin shuttling in a silicon double quantum dot Florian Ginzel, Adam R Mills, Jason Petta, Guido Burkard The transport of quantum information between different nodes of the device is crucial for a quantum processor. In the context of spin qubits, this can be realized by coherent electron spin shuttling between quantum dots. Here we theoretically study a minimal version of spin shuttling between two quantum dots (QDs) occupied by one electron. We analyze the possibilities and limitations of spin transport during a detuning sweep in a silicon double QD. This research is motivated by recent experimental progress [1,2]. Spinorbit interaction and an inhomogeneous magnetic field play an important role for spin shuttling and are included in our model. Interactions that couple the position, spin and valley degrees of freedom open avoided crossings in the spectrum allowing for diabatic transitions and interfering paths. The outcomes of single and repeated spin shuttling protocols are explored by means of numerical simulations and an approximate analytic model based on the LandauZener model. We find that fast highfidelity spinshuttling is feasible for optimal choices of parameters or protected by constructive interference. 
Monday, March 15, 2021 4:12PM  4:24PM Live 
C29.00007: Exploring single Ti/Pd gate layer MOS devices as diagnostic qubits Yanxue Hong, Aruna N Ramanayaka, Ryan Stein, Michael David Stewart, Joshua Pomeroy The design, fabrication, and characterization of MOS quantum dot devices surface gated with a single Ti/Pd metal layer are presented and discussed. The motivation is to avoid using fragile gate dielectrics that are sometimes seen to break down in multilayer devices and obtain simpler process flows. However, as a tradeoff, we expect reduced electrostatic gate control in single layer design. We observed quantum dots forming in the device channel and gate capacitances consistent with modelling, so that dot positions can be located by triangulation in capacitance modelling. In some cases, nondeliberate dot positions and more dots formed than intended, indicate nonlithographic features in the channel. Nonetheless, the gate capacitance ratios are sufficient to enable charge sensing and persistent feedback mode is used to map charge stability regions over wide gate voltage ranges. Granularity and delamination of the Pd layer in the fine region shown by SEM and AFM, combined with possible Si/SiO_{2} interface defects, may account for some of the irregular features in the transport and charge sensing measurements. Overall, these metal single gate layer devices provide ample data for analyzing benefits and costs of this design, and help advancing future implementation of diagnostic qubits. 
Monday, March 15, 2021 4:24PM  4:36PM Live 
C29.00008: Building and Characterizing Orthogonal Gates in a SiMOS ST Qubit Anderson West, Dylan Albrecht, Noah T Jacobson, Tauno Palomaki, Ryan M Jock, Dwight R Luhman Allelectrical control of a singlettriplet qubit in a silicon metaloxidesemiconductor double quantum dot may be realized through the combination of the exchange interaction and intrinsic spinorbit effects at a silicon/silicondioxide interface. Such a qubit operates independently of ancillary components, such as micromagnets or microwave resonators, that are typically required for qubit control. However, the native control axes of this qubit are nonorthogonal and for quantum computation it is desirable to have orthogonal logic gates. In this work, we demonstrate a set of orthogonal gates that are optimal electrical control solutions incorporating composite exchange and spinorbit dominated gates. We assess the performance of these composite orthogonal gates using gate set tomography and Clifford randomized benchmarking. 
Monday, March 15, 2021 4:36PM  4:48PM Live 
C29.00009: Development of Integrated Device Simulator for Silicon Quantum Bit Design Hidehiro Asai, Shota Iizuka, Tsutomu Ikegami, Junichi Hattori, Koich Fukuda, Hiroshi Oka, Kimihiko Kato, Hiroyuki Ota, Takahiro Mori Silicon qubits have attracted much attention as a building block of quantum computers (QCs) because of their huge potential for mass production. However, at this stage, the number of silicon qubits in operation is limited because an appropriate qubit design methodology is lacking. Therefore, a new simulator for silicon qubit design is strongly required to accelerate the development of QCs. 
Monday, March 15, 2021 4:48PM  5:24PM Live 
C29.00010: Controlling and measuring quantum dot qubits in Si/SiGe heterostructures Invited Speaker: Mark Eriksson In this talk I describe two recent advances in the control and measurement of Si/SiGe quantum dot qubits. In the first part of the talk, I describe how relatively small changes in gate voltage can lead to dramatic tunability of 2electron energy eigenstates, which are important for readout of LossDivincenzo, singlettriplet, and quantum dot hybrid qubits. For the latter qubit, the ability to choose, on demand, singlettriplet splittings in neighboring quantum dots is particularly useful, because this splitting determines (in the first dot) the qubit zerotoone energy splitting and (in the second dot) the energy gap for qubit readout. I will show data from the same device demonstrating singlettriplet splittings varying from below 5 GHz up to 15 GHz. In the low frequency end of this range we demonstrate the key role of electronelectron correlations and Wigner molecule physics. I also present data on the use of threedimensional integration in dispersive readout measurement schemes for Si/SiGe quantum dot qubits, and I discuss the implications for scaling of qubit numbers. 
Monday, March 15, 2021 5:24PM  5:36PM Live 
C29.00011: Toward scalable spin qubits: Si/SiGe quantum dot devices built on a 300mm process line Brennen Mueller, Stephanie Bojarski, Hubert C George, Eric Henry, Otto Zietz, Samuel Neyens, Thomas Watson, Rambert Nahm, Payam Amin, Roman Caudillo, Ravi Pillarisetty, Roza Kotlyar, Lester Lampert, Florian Luthi, Jessica Torres, Jeanette Marie Roberts, Jim Clarke Spin qubits in Si/SiGe heterostructures offer a promising platform on which to build a scalable quantum computer. However, fabricating these heterostructures and devices on an alloptical, 300mm process line presents many challenges. One challenge is in creating lateral confinement of the quantum dots. Intel’s SiMOS device architecture is based on fins for lateral confinement, but the formation of fins on Si/SiGe would degrade the strain of the buried silicon quantum well. In this talk, we present a planar device architecture built on a 300mm platform that does not rely on fins for confinement. This planar device is fabricated on a Si/SiGe heterostructure, allowing quantum dots to be formed in a strained silicon quantum well. We will detail progress made on the SiGe virtual substrate and heterostructure, as well as preliminary low temperature measurements. 
Monday, March 15, 2021 5:36PM  5:48PM On Demand 
C29.00012: All Optical 300mm process line for spin qubit devices Hubert C George, Stephanie Bojarski, Eric Henry, Brennen Mueller, Ravi Pillarisetty, David J Michalak, Thomas Watson, Lester Lampert, Samuel Neyens, Otto Zietz, Roman Caudillo, Florian Luthi, Roza Kotlyar, Jeanette Marie Roberts, Jim Clarke Intel has established a 300mm process line for the fabrication of spin qubit devices using all optical lithography. The customized QC testchip provides a diversity of test structures: Transistors, Hall Bars, Quantum Dots, and qubit devices at varying dimensions and 1D array size. Each wafer has ~80 die with thousands of devices, which allows statistical process control of yield and performance. We have implemented testing at industrial scale, with devices/processes that can be characterized inhouse at room temperature and low temperature (1.6K). In this talk, we will provide an overview of integration scheme and yield. We will also discuss key device metrics at both room and low temperatures, in addition to the standard QD/qubit metrics which are normally used. We will present the progress from Transistor to QD devices, and for the first time, we will demonstrate full 300mm spin qubit devices with performance comparable to leading academic devices. 
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