Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F39: Semiconductor Qubits IIIFocus Recordings Available

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Sponsoring Units: DQI DCMP Chair: Vanita Srinivasa, URI Room: McCormick Place W196A 
Tuesday, March 15, 2022 8:00AM  8:36AM Withdrawn 
F39.00001: Coupling semiconductor electron and hole spin qubits to superconducting resonators Invited Speaker: Monica Benito The latest experimental progress in fabrication of one and twodimensional sizable arrays of QDs suggest that quantum information science applications are feasible in these devices, as originally envisioned by Loss and DiVincenzo. Spin qubits in Si and Ge are considered strong candidates for realizing a largescale quantum processor due to the small qubit dimensions, compatibility with CMOS technology, long coherence times and possibility to operate beyond 1 Kelvin. Important challenges concerning scalability of spin qubits defined on QDs can be overcome by turning the qubits electrically addressable. In the case of electrons one can take advantage of the intrinsic spinorbit (SO) coupling or gradients of magnetic field (for example created by external micromagnets). The physics of holes, dictated by the LuttingerKohn Hamiltonian, has attracted much attention lately because it naturally brings the electrical handle thanks to a strong SO coupling without analogous in electron systems. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F39.00002: Spin decoherence due to Ampere field fluctuation from acoustic phonons Xiaoliang Zhang, Yu Yue, Jia Chen, Sam Dillon, Yiyuan Chen, Haiping Cheng, Xiaoguang Zhang We compute the decoherence time of electron spin under the magnetic field produced by the phonon motion of the ions. By using the linear dispersion relation in elastic mediums, the magnetic field due to acoustic phonon motion and the time correlation function of the magnetic field are calculated numerically. We then solve the Redfield equation of motion for the reduced density matrix, which yields the decoherence time of electron spin from the time correlation function of the magnetic field. The calculations are carried out for both in NV center and in semiconductor quantum dots. The NV center result of SiC shows the onsite field dominates the decoherence time. The quantum dot calculation of GaAs, InSb, and InAs shows all atoms in dot contribute. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F39.00003: Anisoptropy and Mixing of Surface Acoustic Waves Zongye Wang

Tuesday, March 15, 2022 9:00AM  9:12AM 
F39.00004: Towards HighImpedance Surface Acoustic Wave Resonators for Quantum Information Processing Tze Yu Li, Yadav P Kandel, John Nichol Inspired by quantum circuit electrodynamics systems, quantum acoustic devices, like surface acoustic wave (SAW) resonators have emerged as powerful tools for quantum information processing in the gigahertz frequency range. Specifically, piezoelectric SAW resonators could be used to couple distant spin qubits in semiconductor quantum dots. Potential benefits of SAW resonators as quantum interconnects include the ability to operate in high magnetic fields and at elevated temperatures. However, strong spinphonon coupling requires a large characteristic impedance associated with the SAW resonator. We discuss our efforts toward realizing SAW resonators with characteristic impedances exceeding 50Ω. To reach such levels of impedance, we use Gaussian SAW resonators on LiNbO_{3} to generate tightly confined phonon modes with strong piezoelectric coupling. Apart from the possibility of coupling distant spin qubits, these highimpedance SAW resonators may also be useful for interfacing microwave and optical photons for quantum information processing. 
Tuesday, March 15, 2022 9:12AM  9:24AM 
F39.00005: Configuration interaction modeling of Si resonant exchange qubits for spinphoton coupling Samuel Quinn Future platforms for scalable quantum information processing, such as spin qubits, will require the capability to entangle qubits over long physical distances. A tantalizing proposal in this space is the capacity to couple triplequantumdot (TQD) spin qubits via a microwave resonator. This is possible in socalled “resonant exchange” (RX) voltage regimes, wherein the system possesses a nonvanishing transverse dipole moment, giving rise to a fast spinphoton coupling rate. In this talk, we detail how numerical simulations of such regimes using configuration interaction (CI) techniques reveal qualitative insights not captured in simpler models. In particular, we show how a distinct RX regime, which we term “XRX,” may be a good candidate for realworld TQDresonator coupling [1]. Our results demonstrate how detailed modeling of the exact multielectron wavefunctions is critical for realistic implementation of spinphoton coupling protocols, as well as exchange operation in general. 
Tuesday, March 15, 2022 9:24AM  9:36AM 
F39.00006: Si/SiGe Single Spin Qubit Devices Enabled by Advanced Semiconductor Fabrication Lester F Lampert, Stephanie A Bojarski, Felix Borjans, Hubert C George, Eric M Henry, Roza Kotlyar, Florian Luthi, Samuel Neyens, Ravi Pillarisetty, Mick Ramsey, Simon Schaal, Thomas F Watson, Guoji Zheng, otto k zietz, Jeanette M Roberts, James S Clarke Reaching quantum practicality, where a quantum computer can solve useful problems, will likely require a million qubits. Semiconductorbased quantum computers can use advanced semiconductor manufacturing, making this a promising approach for scaling qubit count. But to take full advantage of this we need to take all the tools used to make massively scaled transistors devices and apply them to spinqubit devices. However, quantum bits are more fragile than classical bits and require cryogenic systems for operation and testing. To enable the fast feedback methodology used in industry, the 300mm cryoprober was developed; it measures entire wafers at 1.6K. This tool allows downselection of spin qubit devices for measurements in a dilution fridge and also provides critical feedback on fabrication processing. This has led to highly coherent Si/SiGe spin qubit devices fabricated using EUV lithography. Here, we'll discuss bringing highvolume tools and methods to the fabrication of spin qubit devices, including extending these to cryogenic temperatures. We observe wellcontrolled, stable, quantum dot devices with independent barrier control. Qubit control is achieved using EDSR with onchip micromagnets. The results are reproducible on multiple devices and fridges. 
Tuesday, March 15, 2022 9:36AM  9:48AM 
F39.00007: ElectrontoNuclear Spectral Mapping via "Galton board" Dynamic Nuclear Polarization Arjun Pillai, Moniish Elanchezhian, Teemu Virtanen, Sophie Conti, Ashok Ajoy We report on a strategy to indirectly readout the spectrum of an electronic spin via polarization transfer to nuclear spins in its local environment. The nuclear spins are far more abundant and have longer lifetimes, allowing repeated polarization accumulation in them. Subsequent nuclear interrogation can reveal information about the electronic spectral density of states. We experimentally demonstrate the method for reading out the ESR spectrum of NitrogenVacancy center electrons in diamond via readout of lattice ^{13}C nuclei. Spinlock control on the ^{13}C nuclei yields significantly enhanced signaltonoise for the nuclear readout. Spectrally mapped readout presents operational advantages in being backgroundfree and immune to crystal orientation and optical scattering. We harness these advantages to demonstrate applications in underwater magnetometry. The physical basis for the “onetomany” spectral map is itself intriguing. To uncover its origin, we develop a theoretical model that maps the system dynamics, involving traversal of a cascaded structure of LandauZener anticrossings, to the operation of a tilted “Galton board”. This work points to new opportunities for “ESRviaNMR” in dilute electronic systems, and in hybrid electronnuclear quantum memories and sensors 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F39.00008: Tunable interdot coupling in SiMOS architectures over more than nine orders of magnitude Vivien Schmitt, Boris BrunBarriere, YannMichel Niquet, Nicolas Piot, Simon Zihlmann, Xavier Jehl, Tristan Meunier, Maud Vinet, Romain Maurand, Silvano De Franceschi Silicon MOS and SiliconGermanium heterostructures have been proven as a viable route for scalable solidstate quantum computing [1]. Singlequbits operation can routinely exceed 99% [2,3] and have coherence time exceeding few ms. For twoqubit gates, fidelities reaching 98% for electrons in Silicon have been shown [4], but the strength of the Heisenberg exchange interaction, mainly controlled by the tunnel rate between the two hosting dots, remains hard to control. 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F39.00009: Proposal for a cavitymediated measurement of the exchange interaction in a triple quantum dot Florian Ginzel, Guido Burkard In spin qubit arrays the exchange coupling can be harnessed to implement twoqubit gates and to realize intermediaterange qubit connectivity along a spin bus. In this work, we propose a scheme to characterize the exchange coupling between electrons in adjacent quantum dots. We investigate theoretically the transmission of a microwave resonator coupled to a triple quantum dot occupied by two electrons. We assume that the right quantum dot (QD) is always occupied by one electron while the second electron can tunnel between the left and center QD. If the two electrons are in adjacent dots they interact via the exchange coupling. By means of exact analytical expressions we show that the transmission profile of the resonator directly reveals the value of the exchange coupling strength between two electrons. From perturbation theory up to second order we conclude that the exchange can still be identified in the presence of magnetic gradients. In case of a lifted valley degeneracy prior knowledge about the valley splitting and valley phase differences is important to correctly identify the transmission dips and thus the exchange coupling. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F39.00010: Coupling Quantum Dots to 2DEGBased SuperconductorSemiconductor Hybrids Alisa Danilenko, Andreas S PĂ¶schl, Deividas Sabonis, Tyler Lindemann, Sergei Gronin, Geoffrey C Gardner, Candice Thomas, Michael J Manfra, Charles M Marcus We present experimental results for gatedefined lateral quantum dots coupled to a superconductorsemiconductor nanowire based on InAs/Al twodimensional electron gas (2DEG). We demonstrate independent voltage control of coupling of multiple quantum dots to the superconducting wire on one side and normal semiconducting leads on the other. This provides experimental control of hybridization of discrete dot states to subgap Andreev states in the wire [1,2] and a tool for highresolution spectroscopy of Andreev states [3], as well as a possibility to use the dots as filters [4]. A high degree of experimental control as well as extension to a variety of device geometries is made possible by the hybrid 2DEG platform. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F39.00011: Theory of coherent spin transfer between two semiconductor quantum dots Jan A Krzywda, Lukasz Cywinski Longdistance transfer of quantum information in quantum dots (QDs) spin qubits will be necessary for their scalability [1]. One way of achieving this goal is to move the electron between tunnelcoupled QDs using a sweep of their energy detuning [2, 3]. We present here an analysis showing how coherent transfer of spin superposition is affected by electronphonon scattering and charge noise in detuning and tunnel coupling at finite temperature. We have predicted that probability of charge transfer can be nonmonotonic function of transfer time, and predicted that the error below 0.001 requires tunnel couplings above 20µeV, as it has been confirmed experimentally in Si/SiGe [3] and SiMOS [4]. Next we analyzed to what extent electron transfer modifies the spin coherence and uncovered that in absence of nuclear spins, main dephasing mechanisms are activated by a difference of Zeeman splittings in the QDs, which leads to: shortterm creation of charge qubit and random phase rotation during temporal occupation of higher energy state. 
Tuesday, March 15, 2022 10:36AM  10:48AM 
F39.00012: Coherent spinvalley oscillations in silicon Xinxin Cai, Elliot J Connors, John Nichol Electron spins in silicon quantum dots are excellent qubits because they have long coherence times, high gate fidelities, and are compatible with advanced semiconductor manufacturing techniques. The valley degree of freedom, which results from the specific character of the Si band structure, is a unique feature of electrons in Si spin qubits. However, the small difference in energy between different valley levels often poses a challenge for quantum computing in Si. Here, we show that the spinvalley coupling in Si, which enables transitions between states with different spin and valley quantum numbers, enables coherent electronspin manipulation in Si. We demonstrate coherent manipulation of effective single and twoelectron spin states in a Si/SiGe double quantum dot without ac magnetic or electric fields. Our results illustrate that the valley degree of freedom, which is often regarded as an inconvenience, can itself enable quantum manipulation of electron spin states. 
Tuesday, March 15, 2022 10:48AM  11:00AM Withdrawn 
F39.00013: Balancing coherent and dissipative dynamics in a centralspin system Bill Coish, Alessandro Ricottone, Yinan Fang The average time required for an open quantum system to reach a steady state (the steadystate time) is generally determined through a competition of coherent and incoherent (dissipative) dynamics. Here, we study this competition for a ubiquitous centralspin system, corresponding to a centralspin1/2 coherently coupled to ancilla spins and undergoing dissipative spin relaxation. The ancilla system can describe N spins1/2 or, equivalently, a single large spin of length I = N/2. We find exact analytical expressions for the steadystate time in terms of the dissipation rate, resulting in a minimal (optimal) steadystate time at an optimal value of the dissipation rate, according to a universal curve. Due to a collectiveenhancement effect, the optimized steadystate time grows only logarithmically with increasing N = 2I, demonstrating that the system size can be grown substantially with only a moderate cost in steadystate time. This paper has direct applications to the rapid initialization of spin qubits in quantum dots or bound to donor impurities, to dynamic nuclearspin polarization protocols, and may provide key intuition for the benefits of errorcorrection protocols in quantum annealing. 
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