Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C28: Silicon Spin QubitsFocus
|
Hide Abstracts |
Sponsoring Units: DQI Chair: Susan Coppersmith, Univ of Wisconsin, Madison Room: LACC 405 |
Monday, March 5, 2018 2:30PM - 3:06PM |
C28.00001: Charge Noise Limited Gate Fidelity > 99.9% of Spin Qubits with Si/SiGe Quantum Dots Invited Speaker: Seigo Tarucha Qubit number and error rate are both key parameters to characterize the power of quantum computing, but they are still challenging issues. The underlying physics for the error rate is dephasing due to coupling to the environment noise, magnetic or electrical for the case of spin qubits with quantum dots (QDs). Here I will discuss the spin dephasing measured for QDs made out of GaAs and Si/SiGe and how to suppress the dephasing to raise the gate fidelity well exceeding the threshold of fault tolerant qubit gates. In GaAs QDs the dephasing arises predominantly from the fluctuating nuclear spin bath. This noise is time-correlated and the variance increases with increasing correlation time from msec to 100 sec in the non-ergodic regime. We employ a micro-magnet technique for operating the single snd two spin qubits. We show that both fast gating and feedback control are useful to raise the fidelity exceeding 99 %. On the other hand, in Si QDs the magnetic noise is significantly reduced but electrical noise can be crucial instead. We apply the micro-magnet technique for natural and isotopically purified Si/SiGe QDs and obtain the fidelity exceeding 99.9 % for the isotopically purified Si/SiGe QDs by optimizing the gating speed, and find the fidelity is predominantly limited by charge noise. From this result we can also assign the fidelity of 99.6% obtained for the natural Si/SiGe to magnetic noise of remaining nuclear spins. I will discuss influences from charge fluctuations on the gate fidelity in the presence of a micro-magnet induced stray field. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C28.00002: Coherent electron charge and spin transport in a Silicon double quantum dot Xinyu Zhao, Xuedong Hu We investigate coherent electron transport in a Si double quantum dot. First, we focus on the charge dynamics without considering the spin degree of freedom. We propose a scheme to measure the valley phase difference between two dots by using the Landau-Zener-Stückelburg interference, and examine the experimental feasibility of the proposed scheme. We then consider spin transport and clarify how spin-valley mixing can cause considerable flip error even though spin-orbit coupling is relatively weak in Si. Our results also show that the valley phase difference can significantly affect the fidelity of spin transport. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C28.00003: Valley Splitting in SiGe Quantum Dots Measured Using Pauli Blockade and Single-shot Readout Bo Sun We introduce an in-situ technique to measure the valley splitting energy of SiGe quantum dots at the (2,0)-(1,1) charge boundary, the location of spin-to-charge conversion. Because the valley state is the lowest-energy excited state in many Si based spin qubits, low valley energies can limit the fidelity of both Pauli-blockaded spin readout and singlet initialization. In such systems, we can determine the valley splitting energy by measuring the extent of the Pauli blockade along the bias-voltage controlled detuning axis. In principle, this can be accomplished by comparing the behavior of the (1,1) singlet and (1,1) triplet states as they transition to the (2,0) charge state. Such an experiment would require both high fidelity initialization and calibrated spin rotations, which may be difficult to achieve when the valley splitting is small. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C28.00004: Few-Electron Quantum Dot Magnetospectroscopy Dependences on Tunable Coupling and Confinement Chloe Bureau-Oxton, Dan Ward, John Anderson, Ron Manginell, Joel Wendt, Tammy Pluym, Michael Lilly, Michel Pioro-Ladriere, Malcolm Carroll, Dwight Luhman Magnetospectroscopy is a foundational technique for understanding quantum dots (QDs). It allows the extraction of important information including electron occupation, the lever arm to device gates, as well as the valley and orbital splittings. The complexity of silicon QD systems is increasing, allowing much greater tunability. However, the sensitivity of the QD valley and orbital behavior to the tuning parameters of these QD layouts is not well established. In this work, we measure the magnetospectroscopy of a lithographically-defined few-electron QD in silicon. We report on observed changes to the magnetospectroscopy as a function of QD lateral confinement and tunnel coupling to the reservoirs. The influence of the interaction between the main QD and a second neighboring dot is also investigated. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C28.00005: Effect of an interface step on the Valley Splitting in a Si/SiGe quantum dot Bilal Tariq, Xuedong Hu Valley-orbit coupling, which is generally a complex quantity, is a key parameter for a Si quantum dot in determining its suitability for applications in quantum information processing. With Si conduction band valleys far apart in the First Brillouin Zone, valley-orbit coupling strength is sensitive to the interface roughness. One type of common roughness at interface is steps in Si composition. Using effective mass approximation, here we explore how the position of a step or steps at the interface affects the energy levels of an electron in a Si/SiGe quantum dot. We include higher-energy orbital levels, Umklapp processes, and Bloch states in our calculation. Our results show that the magnitude of valley splitting is mostly determined by the envelop function, and generally decreases when a step is introduced. The phase of the valley-orbit coupling is also affected by the step(s) through the envelope function. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C28.00006: Implications of the Spin-Orbit Effect for Singlet-Triplet Qubit Operation Patrick Harvey-Collard, Noah Jacobson, Ryan Jock, Andrew Mounce, Vanita Srinivasa, Daniel Ward, Joel Wendt, Martin Rudolph, Tammy Pluym, John Gamble, Wayne Witzel, Michel Pioro-Ladriere, Malcolm Carroll Spin-orbit effects in silicon have long been considered of minor importance for the operation of spin qubits. In this work, we use a silicon MOS double quantum dot singlet-triplet qubit as a sensitive probe of the spin-orbit effect. We first show that a strong magnetic field enables rotations between the singlet S and triplet T0, an effect which amounts to an effective g-factor difference between the two quantum dots. Two-axis control and single shot readout of the qubit is used to study AC resonant control and achieve few microsecond Rabi flip times. Secondly, we investigate a different effect of the spin-orbit interaction on the S-T− transition and its impact on schemes like dynamic nuclear polarization. Our results shed light on the implications of spin-orbit interaction for the operation of spin qubits in silicon. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C28.00007: Spin-orbit coupling induced two-electron relaxation in coupled silicon donors Yang Song We discovered theoretically the unexpected important role of intrinsic donor spin-orbit coupling (SOC) in driving the relaxation of coupled-donor electron states in isotopically enriched silicon 28, which is a promising host material for semiconductor qubits, despite the commonly perceived weak strength of atomic SOC in this material. The only existing spin-relaxation mechanism considered in this context before our work is the relaxation of two-electron states induced by hyperfine interaction with the donor nuclear spins. The new intrinsic SOC mechanism has a parametrically strong dependence on exchange coupling (~J5), and becomes important when the donors are closely spaced as in the case of singlet-triplet spin qubits. Our analytical study drew on the symmetry analysis over combined band, donor envelope and valley configurations, and unraveled naturally the anisotropic dependence on the donor-alignment direction and triplet spin orientation and the associated phonon modes. This mechanism may also shed important new light on the well-studied problem of electron spin resonance in highly doped silicon. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C28.00008: Spin Relaxation in Si/SiGe Quantum Dot Devices with Micromagnets Felix Borjans, David Zajac, Jason Petta Recent quantum control experiments in Si/SiGe quantum dots utilizing a micromagnet for electrically driven spin resonance have reported spin relaxation times (T1) ranging from 4 ms to more than 50 ms [1,2]. These T1 times are shorter than those obtained on samples without micromagnets, which suggests that the presence of the micromagnet is limiting T1 [3,4]. We measure T1 in a Si/SiGe device incorporating a micromagnet up to a magnetic field of 6 T. We find a saturation of T1 at low fields, evidence of a valley relaxation hotspot, and a soft B3 field dependence above 2 T. These measurements indicate that the spin-orbit coupling induced by the micromagnet causes otherwise suppressed relaxation channels to dominate and limit qubit performance. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C28.00009: 300mm process line for qubit fabrication Hubert C George, Kanwal Singh, Ravi Pillarisetty, Nicole Thomas, Jelmer Boter, Delphine Brousse, J.P Dehollain, Gabriel Droulers, GertJan Eenink, Nico Hendrickx, Nima Kalhor, Nodar Samkharadze, Amir Sammak, LaReine Yeoh, Diego Sabbagh, Giordano Scappucci, Menno Veldhorst, Lieven Vandersypen, James Clarke The 300mm fabrication process is the backbone for advanced technology nodes in the semiconductor industry. State of the art transistors most complex integration schemes are only possible using the unique patterning capabilities, high quality material deposition, and process control that are maintained at these facilities. Intel is leveraging its 300mm fabrication expertise to create spin qubit circuits for quantum computing applications. This talk will focus on three aspects: materials, integration, and characterization. Intel has established a supply of high quality material which includes highly purified Si-28 for long coherence times. We also have created a multi-mask integration scheme which involves custom designed masks that allow fabrication of production quality quantum dots and spin qubits alongside reference transistors. We will be discussing some of the preliminary results from the 300 mm fab and lab line such as structures/features variation which is imperative for qubit devices. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C28.00010: Designing for strain in silicon quantum dot devices N. Tobias Jacobson, Daniel Ward, Andrew Baczewski, John Gamble, Martin Rudolph, Malcolm Carroll Mechanical strain, established as a result of thermal expansion mismatch during cooling to cryogenic temperatures and the steps of device fabrication, may significantly alter the potential landscape experienced by electrons in electrostatically-defined silicon quantum dot devices. Through simulating the established strain field and incorporating the combined effects of electrostatics and strain on electronic structure, we can quantitatively model device performance. In this talk, we explore the role mechanical strain may play in device operation and propose methods through which one may mitigate deleterious strain effects and, conversely, exploit strain to design a built-in potential landscape. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C28.00011: Charge offset drift in silicon-on-insulator mesa-etched single electron devices with Al gates Binhui Hu, Aruna Ramanayaka, Joshua Pomeroy, Neil Zimmerman, M. Stewart Jr. Charge offset drift in single electron devices (SEDs) deleteriously affects their applications in metrology and quantum computing by complicating integration of devices. Our recent measurements on single-layer SEDs show that the charge offset drift not only depends on the material system, but also depends on the device design.[1] This result prompts us to revisit silicon-on-insulator (SOI) mesa-etched SEDs. Previous results show that the charge offset drift is minimal in SOI devices with a polySi/SiO2/Si gate stack (ΔQ0<0.01e),[2] while devices made on bulk wafers with an Al/SiO2/Si gate stack show higher levels of drift (ΔQ0~0.15e). [3] In this work, we keep the device geometry and structure of the SOI devices but modify the gate stack to be Al/SiO2/Si. We will present the charge offset drift results on these SOI mesa-etched SEDs with Al gates. The individual roles being played by the material system and the device structure in determining the level of charge offset drift will be discussed. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C28.00012: Non-equilibrium Si Valley Quantum Dots : Devices and Spectroscopy Bijay Agarwalla, Manas Kulkarni, Guido Burkard Motivated by the recent experiment on highly resolved valley spectroscopy for Si double quantum dots [1] in a circuit-QED architecture, we show that [2] such setups have the potential to perform as excellent quantum devices (for e.g, microwave amplifiers). We investigate this setup by employing the diagrammatic Keldysh Non-equilibrium Greens function's approach [3,4] and study the gain in the microwave photon transmission. This diagrammatic technique further provides a systematic and transparent way to understand the small energy/valley splitting in the low-lying Si energy states as captured in the transmission spectroscopy via multiple dips [5]. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C28.00013: Measurements of Shubnikov-de Haas effect in highly enriched 28Si Hall bars Aruna Ramanayaka, Hyun-soo Kim, Ke Tang, Joseph Hagmann, Curt Richter, M. Stewart Jr., Joshua Pomeroy Elimination of unpaired nuclear spins can improve the fidelity of the quantum information; therefore, isotopically enriched 28Si is regarded as an ideal environment for quantum information processing devices. Using mass selected ion beam deposition technique, we in-situ enrich and deposit epitaxial 28Si and routinely achieving better than 99.99998 % 28Si isotope fractions. To explore the electrical properties and optimize the growth conditions of in-situ enriched 28Si, we fabricate top gated Hall bar devices, and investigate the magnetotransport in this material at magnetic fields as high as 12 T and temperature ranging from 20 K to 1.2 K. The data at low magnetic fields [endif]--> shows maximum mobilities of approximately 2500 cm2/Vs and 5000 cm2/Vs at an electron density of ≈ 2.5 x 1012 cm-2 for devices fabricated on 28Si and natural Si, respectively. Temperature dependence of Shubnikov-de Hass oscillations in longitudinal magnetoresistance (Rxx) at B > 2 T is used to extract the effective mass for charge carriers. Here, we report on the above device metrics, and compare to similar devices fabricated on natural Si. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700