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 J29: Semiconductor Qubits IIFocus Live

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Sponsoring Units: DQI Chair: Dwight Luhman, Sandia National Laboratories 
Tuesday, March 16, 2021 3:00PM  3:12PM Live 
J29.00001: Systematic charge noise characterization of Intel quantum dot devices Florian Luthi, Roman Caudillo Quantum computing promises to tackle exciting and computationally difficult problems. Intel is leveraging 50 years of experience in semiconductor manufacturing to develop siliconbased spin qubit devices. A key challenge in this endeavor is reducing the effect of noise on the spin qubits to an acceptable level. The effects of noise can be reduced by lowering its strength or the sensitivity of the qubits to the noise. For spin qubits, charge noise is an important contributor, limiting coherence and gate fidelity. The impact of charge noise can be mitigated with fabrication changes, so it is important to acquire statistically relevant data in a systematic way. We find that the level of charge noise can vary considerably depending on the configuration of the quantum dot that hosts the spin qubit. Therefore, we measure the noise over large parameter ranges on many quantum dots. Using fast noise measurements, we find twolevel systems that increase charge noise excessively. Further, we confirm the linear dependence of charge noise on temperature. Using a cryogenic wafer probing tool that enables efficient 300mmwaferscale measurements at 1.6 K, we can inform fabrication decisions with statistically relevant data. We also highlight the expected impact of noise on system performance. 
Tuesday, March 16, 2021 3:12PM  3:24PM Live 
J29.00002: A fourqubit germanium quantum processor Nico Hendrickx, Will Lawrie, Maximilian Russ, Floor van Riggelen, Sander de Snoo, Raymond Schouten, Amir Sammak, Giordano Scappucci, Menno Veldhorst Quantum dot spin qubits are a promising platform for largescale quantum computers. Their inherent compatibility with semiconductor fabrication technology promises the ability to scale up to large numbers of qubits. However, all prior experiments are limited to twoqubit logic. 
Tuesday, March 16, 2021 3:24PM  3:36PM Live 
J29.00003: A depletion mode hole spinqubit in Ge Daniel Jirovec Spin qubits are considered to be among the most promising candidates for building a quantum processor [1] with group IV semiconductors standing out for their long coherence times and CMOS integrability. Recently, holes in Ge have proven scaleup beyond two qubits with a 4 LossDiVincenzo qubit device realized [2]. Here we demonstrate a spin qubit in a Ge/SiGe heterostructure realized with a single layer of confinement gates. We observe fast electrically controlled X and Zrotations exceeding 100 MHz with dephasing times of 1 μs which we extend beyond 10 μs with echo techniques. The extracted noise spectral density suggests that the dephasing time is limited by low frequency fluctuations which we attribute to nuclear spins. The reported results demonstrate that holes in Ge are a viable candidate for integration into a large scale quantum processor. 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J29.00004: Cavity control over heavyhole spin qubits in inversionsymmetric crystals Philipp Mutter, Guido Burkard The pseudospin of heavyholes confined in a semiconductor quantum dot represents a promising candidate for a fast and robust qubit. While hole spin manipulation by a classical electric field utilizing the Dresselhaus spinorbit interaction has been demonstrated, our work explores cavitybased qubit manipulation and coupling schemes for inversionsymmetric crystals forming a planar heavyhole quantum dot. Choosing the exemplary material Germanium, we derive an effective cavitymediated ground state spin coupling that harnesses the cubic Rashba spinorbit interaction. In addition, we propose an optimal set of parameters which allows for Rabi frequencies in the MHz range, thus entering the strong coupling regime of cavity quantum electrodynamics. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J29.00005: A hot hole spin qubit in a silicon FinFET Simon Geyer, Leon Camenzind, Mathieu de Kruijf, Andreas Fuhrer, Richard J. Warburton, Dominik Zumbuhl, Andreas V. Kuhlmann Quantum computers promise an exponential speedup for certain computational tasks. Siliconbased spin qubits are among the prime candidates for implementing largescale quantum circuits by leveraging widely deployed industrial CMOS technology. Furthermore, qubit operation at temperatures above 1K allows for onchip integration of classical control electronics [Petit et al. & Yang et al., Nature 580, 350&355 (2020)]. 
Tuesday, March 16, 2021 4:00PM  4:12PM Live 
J29.00006: Pseudospinelectric coupling for holes beyond the envelopefunction approximation Bill Coish, Pericles Philippopoulos, Stefano Chesi, Dimitrie Culcer We have calculated [1] the electricdipole (pseudospinelectric) coupling between heavy and light holes in GaAs from first principles. We find a transition dipole of 0.5 debye, a significant fraction of that for the hydrogenatom 1s→2p transition. In addition, we derive the Dresselhaus spinorbit coupling that is generated by this transition dipole for heavy holes in a triangular quantum well. A quantitative microscopic description of this pseudospinelectric coupling may be important for understanding the origin of spin splitting in quantum wells, spin coherence/relaxation (T_{2}^{*}/T_{1}) times, spinelectric coupling for cavityQED, electricdipole spin resonance, and spin nonconserving tunneling in double quantum dot systems. Related results for the firstprinciples calculation of hyperfine couplings [2] for holes in GaAs, silicon, and germanium will also be discussed. 
Tuesday, March 16, 2021 4:12PM  4:24PM Live 
J29.00007: Quantum coherence benchmarks and coherent control of hole spin qubits in a 2x2 germanium quantum dot array William Iain Lawrie, Nico Hendrickx, Floor Van Riggelen, Maximilian Russ, Luca Petit, Amir Sammak, Giordano Scappucci, Menno Veldhorst The spin state of an elementary charge is a wellestablished candidate for quantum information processing. Multiple semiconductor platforms are presently under considerable study to determine their viability as host materials for spin qubits, in particular their suitability as hosts of scalable qubit unit cells. 
Tuesday, March 16, 2021 4:24PM  4:36PM Live 
J29.00008: Measurement of the outofplane gfactor in strained Ge/SiGe using singlehole quantum dots Andrew J Miller, Mitchell Brickson, Will J Hardy, ChiaYou Liu, JiunYun Li, Andrew D Baczewski, Michael P Lilly, TzuMing Lu, Dwight R Luhman Lithographically patterned quantum dots in strained Ge/SiGe have become promising candidates for quantum computing, with a quick progression to qubit logic demonstrations. Here we present an experimental measurement of the outofplane gfactor in this material for a single hole confined to a quantum dot, which avoids the strong orbital effects that can occur in this configuration. Strong asymmetry of the gfactor between the in and outofplane directions is seen. These results are in agreement with calculations using the Luttinger Hamiltonian and suggest dramatic tunability through both the Bfield and the charge state. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J29.00009: LightHole States in Highly TensileStrained Ge Quantum Well Anis Attiaoui, Simone Assali, Patrick DelVecchio, Oussama Moutanabbir Sicompatible lowdimensional systems have been exploiting either tensile strained Si or compressively strained Germanium (Ge) quantum wells (QWs). For quantum information, the latter has been explored in new schemes for hole spin qubits. Hole spins have attracted a great deal of attention. Nevertheless, most of experimental investigations on 2D gas systems have so far focused on heavyhole states (HH) due to the compressively strained heterostructure currently exploited, where the valence band degeneracy is lifted and leaves HH states energetically above the lighthole (LH) states. However, the ability to exploit LH states will be a powerful paradigm beneficial for quantum information technologies. To harness these largely unexplored advantages of LH states, we present a new lowdimensional system consisting of highly tensile strained Ge quantum well grown on Si wafers using GeSn as barriers. Several spectroscopic techniques were used to identify the LH confined states in the Ge well. The obtained heterostructure shows optical transitions that are modulated in the midinfrared range. This ability to engineer quantum structure where LH is the ground state in an optically active group IV platform lays the groundwork for a new class of Sicompatible quantum technologies. 
Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J29.00010: Isotropic and Anisotropic gfactor Corrections in GaAs Quantum Dots Leon Camenzind, Simon Svab, Peter Stano, Liuqi Yu, Jeramy D Zimmerman, Arthur C Gossard, Daniel Loss, Dominik Zumbuhl The spin splitting is a fundamental property of an electron confined in a semiconductor in an external magnetic field and sets the qubit energy – a key parameter for quantum computation. Here, we experimentally determine isotropic and anisotropic gfactor corrections in lateral GaAs singleelectron quantum dots (Camenzind, Svab et al., arXiv:2010.11185 (2020)). We extract Zeeman splittings by measuring tunnel rates into individual spin states of an empty quantum dot for various inplane magnetic field strengths/directions. We find an anisotropic correction of ≈7% of the average gfactor, in good agreement with recent theory (Stano et al. PRB98, 195314 (2018)), where this is due to Dresselhaus spinorbit interaction (SOI) using a coefficient of 10.6 eVÅ^{3}. The isotropic correction is measured to reduce the average gfactor 1015% below the bulk value g=0.44, due to Rashba SOI and an additional ''43term'' SOI. These corrections are predicted to depend strongly on the thickness of the wave function in the zdirection perpendicular to the 2D gas. These findings provide the fundamental physics of the singleelectron spin splitting and as such are at the heart of GaAs spin qubits. 
Tuesday, March 16, 2021 5:00PM  5:12PM Live 
J29.00011: Modeling resonant tuning of hole gtensors and underlying mechanisms in quantum dot molecules Arthur Lin, Matthew F Doty, Garnett Bryant Hole spins in InAs/GaAs quantum dot molecules (QDMs) show promise as semiconductor spin qubits, as hole states are weakly coupled to nuclear spins. QDMs are desired over single dots for the tunability of molecular states, formed by QD states brought to resonance with applied electric fields. Near resonance, the Zeeman splitting of these molecular hole states can be enhanced or suppressed, providing electrical tuning of the hole gtensor. The formation and tunability of these states is well observed experimentally. Here, we provide an atomistic tightbinding theory for this tuning of Zeeman splitting to elucidate the mechanism for this enhancement and to identify ways to further manipulate the hole gtensor. We find that the gtensor tunability near resonance is explained by a strong enhancement or suppression of coupling between the spatial motion of the hole state and the magnetic field, as described in our theory by a Peierls term. In contrast, there is no change in the hole spin or leakage into the interdot barrier near resonance. Phenomenological modeling suggests that spindependent interdot tunneling is the mechanism for the gtensor tunability. We use our atomistic theory to explore the spatial implications of spindependent tunneling to critically assess this mechanism. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J29.00012: Pulse shaping for a robust CZ gate in a silicon threequbit device with alwayson exchange David Kanaar, Sidney Wolin, Utkan Güngördü, Jason Kestner We theoretically consider a 3qubit system of electron spins in a silicon triple quantum dot with alwayson exchange coupling. We have shown how to perform local spin rotations and 2qubit entangling gates between neighboring qubits in the absence of noise, these form a universal set. However, in practice, low fidelity due to noise is an important limitation of quantum devices, so it is necessary to create gates robust against noise. In this talk we will show how to make a CZ gate robust against charge noise, the most important noise in the silicon 3qubit device. Using the fact that the hamiltonian accrues error in two separately controlled and commuting SU(2) subspaces we apply the pulse shaping method of Ref.[1] simultaneously in both spaces. Matching the pulse time in both spaces leads to a pulse that is robust to both fluctuations in exchange coupling and the electron gfactor induced by charge noise. The robust pulse maintains a fidelity of 10^{4} at 3.5% fluctuations in exchange or gfactor, an improvement over the 1% for the naive pulse. 
Tuesday, March 16, 2021 5:24PM  6:00PM Live 
J29.00013: High Fidelity Spin Readout in a CMOS Device Invited Speaker: Matias Urdampilleta Over the last fifty years, the CMOS (ComplementaryMetalOxideSemiconductor) electronics industry has been continuously scaling down transistors in size, to increase performance and reduce power consumption. Nowadays, the smallest transistors in industry achieve 5nm features. As a result, those silicon structures tend to exhibit undesirable quantum effects for a classical transistor which appear to be new research opportunities for quantum information processing. 
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