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Randomized compiling for scalable quantum computing on a noisy superconducting quantum processor

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arXiv 2020年

作者： Hashim, Akel Naik, Ravi K. Morvan, Alexis Ville, Jean-Loup Mitchell, Bradley Kreikebaum, John Mark Davis, Marc Smith, Ethan Iancu, Costin O'Brien, Kevin P. Hincks, Ian Wallman, Joel J. Emerson, Joseph Siddiqi, Irfan Quantum Nanoelectronics Laboratory Department of Physics University of California at Berkeley BerkeleyCA94720 United States Graduate Group in Applied Science and Technology University of California at Berkeley BerkeleyCA94720 United States Computational Research Division Lawrence Berkeley National Lab BerkeleyCA94720 United States Materials Sciences Division Lawrence Berkeley National Lab BerkeleyCA94720 United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA United States Quantum Benchmark Inc. KitchenerONN2H 5G5 Canada Institute for Quantum Computing and Department of Applied Mathematics University of Waterloo WaterlooONN2L 3G1 Canada

The successful implementation of algorithms on quantum processors relies on the accurate control of quantum bits (qubits) to perform logic gate operations. In this era of noisy intermediate-scale quantum (NISQ) computing, systematic miscalibrations, drift, and crosstalk in the control of qubits can lead to a coherent form of error which has no classical analog. Coherent errors severely limit the performance of quantum algorithms in an unpredictable manner, and mitigating their impact is necessary for realizing reliable quantum computations. Moreover, the average error rates measured by randomized benchmarking and related protocols are not sensitive to the full impact of coherent errors, and therefore do not reliably predict the global performance of quantum algorithms, leaving us unprepared to validate the accuracy of future large-scale quantum computations. Randomized compiling is a protocol designed to overcome these performance limitations by converting coherent errors into stochastic noise, dramatically reducing unpredictable errors in quantum algorithms and enabling accurate predictions of algorithmic performance from error rates measured via cycle benchmarking. In this work, we demonstrate significant performance gains under randomized compiling for the four-qubit quantum Fourier transform algorithm and for random circuits of variable depth on a superconducting quantum processor. Additionally, we accurately predict algorithm performance using experimentally-measured error rates. Our results demonstrate that randomized compiling can be utilized to leverage and predict the capabilities of modern-day noisy quantum processors, paving the way forward for scalable quantum computing. Copyright © 2020, The Authors. All rights reserved.

关键词： Benchmarking

Iron nanoparticles with tunable tetragonal structure and magnetic properties

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Physical Review materials 2018年第5期2卷 054415-054415页

作者： Jinming Liu Karl Schliep Shi-Hai He Bin Ma Ying Jing David J. Flannigan Jian-Ping Wang Department of Electrical and Computer Engineering University of Minnesota 200 Union Street SE Minneapolis Minnesota 55455 USA Department of Chemical Engineering and Materials Science University of Minnesota 421 Washington Avenue SE Minneapolis Minnesota 55455 USA

Body-centered cubic (bcc) Fe is known as a typical soft magnetic material with high-saturation magnetization (Ms) and low magnetocrystalline anisotropy. However, first-principles calculations demonstrate that body-centered tetragonal (bct) Fe has higher magnetocrystalline anisotropy than bcc Fe and comparable Ms. In this work, bct Fe nanoparticles (NPs) were successfully fabricated by a gas-phase condensation method for the first time. The bct Fe phase is confirmed by the x-ray diffraction pattern and diffraction images of transmission electron microscopy. An increased magnetocrystalline anisotropy of bct Fe, (2.65±0.67)×105J/m3[(21.2±5.3)μeV/atom], is observed, which is around seven times higher than that of bcc Fe 4.8×104J/m3(3.5μeV/atom). The bct Fe NPs sample has coercivity of 3.22×105 A/m at 5 K and 1.04×105 A/m at 300 K, which are much higher than that of bcc Fe NPs. In addition, the saturation magnetization at 5 K is estimated to be (1.6±0.4)×106 A/m (2.2±0.5μB/atom), comparable to that of bcc Fe 1.7×106 A/m (2.2μB/atom).

关键词： Ferromagnetism Magnetic anisotropy Magnetic phase transitions

Enhancing interconnect reliability and performance by converting tantalum to 2D layered tantalum sulfide at low temperature

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arXiv 2019年

作者： Lo, Chun-Li Catalano, Massimo Khosravi, Ava Ge, Wanying Ji, Yujin Zemlyanov, Dmitry Y. Wang, Luhua Addou, Rafik Liu, Yuanyue Wallace, Robert M. Kim, Moon J. Chen, Zhihong School of Electrical and Computer Engineering Purdue University West LafayetteIN47907 United States Birck Nanotechnology Center Purdue University West LafayetteIN47907 United States Materials Science and Engineering Department University of Texas at Dallas 800 West Campbell Road RichardsonTX75080 United States Via Monteroni ed. A3 Lecce73100 Italy Texas Materials Institute Department of Mechanical Engineering University of Texas at Austin AustinTX78712 United States

The interconnect half-pitch size will reach ~20 nm in the coming sub-5 nm technology node. Meanwhile, the TaN/Ta (barrier/liner) bilayer stack has to be > 4 nm to ensure acceptable liner and diffusion barrier properties. Since TaN/Ta occupy a significant portion of the interconnect cross-section and they are much more resistive than Cu, the effective conductance of an ultra-scaled interconnect will be compromised by the thick bilayer. Therefore, two dimensional (2D) layered materials have been explored as diffusion barrier alternatives. However, many of the proposed 2D barriers are prepared at too high temperatures to be compatible with the back-end-of-line (BEOL) technology. In addition, as important as the diffusion barrier properties, the liner properties of 2D materials must be evaluated, which has not yet been pursued. Here, a 2D layered tantalum sulfide (TaSx) with ~1.5 nm thickness is developed to replace the conventional TaN/Ta bilayer. The TaSx ultra-thin film is industry-friendly, BEOL-compatible, and can be directly prepared on dielectrics. Our results show superior barrier/liner properties of TaSx compared to the TaN/Ta bilayer. This single-stack material, serving as both a liner and a barrier, will enable continued scaling of interconnects beyond 5 nm node. Copyright © 2019, The Authors. All rights reserved.

关键词： Temperature

Unified multi-contact fall mitigation planning for humanoids via contact transition tree optimization

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arXiv 2018年

作者： Wang, Shihao Hauser, Kris Department of Mechanical Engineering and Materials Science Duke University DurhamNC27708 United States Departments of Electrical and Computer Engineering and Mechanical Engineering and Materials Science Duke University DurhamNC27708 United States

This paper presents a multi-contact approach to generalized humanoid fall mitigation planning that unifies inertial shaping, protective stepping, and hand contact strategies. The planner optimizes both the contact sequence and the robot state trajectories. A high-level tree search is conducted to iteratively grow a contact transition tree. At each edge of the tree, trajectory optimization is used to calculate robot stabilization trajectories that produce the desired contact transition while minimizing kinetic energy. Also, at each node of the tree, the optimizer attempts to find a self-motion (inertial shaping movement) to eliminate kinetic energy. This paper also presents an efficient and effective method to generate initial seeds to facilitate trajectory optimization. Experiments demonstrate show that our proposed algorithm can generate complex stabilization strategies for a simulated planar robot under varying initial pushes and environment shapes. Copyright © 2018, The Authors. All rights reserved.

关键词： Aerodynamics

Significantly Reduced Thermal Conductivity in β-(Al0.1Ga0.9)2O3/Ga2O3 Superlattices

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arXiv 2019年

作者： Cheng, Zhe Tanen, Nicholas Chang, Celesta Shi, Jingjing McCandless, Jonathan Muller, David Jena, Debdeep Xing, Huili Grace Graham, Samuel George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30332 United States Department of Materials Science and Engineering Cornell University IthacaNY14853 United States Department of Physics Cornell University IthacaNY14853 United States School of Electrical and Computer Engineering Cornell University IthacaNY14853 United States School of Applied and Engineering Physics Cornell University IthacaNY14853 United States Kavli Institute for Nanoscale Science Cornell University IthacaNY14853 United States School of Materials Science and Engineering Georgia Institute of Technology AtlantaGA30332 United States

β-Ga2O3 has emerged as a promising candidate for electronic device applications because of its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is at least one order of magnitude lower than that of other wide bandgap semiconductors such as SiC and GaN. Thermal dissipation in electronics made from β-Ga2O3 will be the bottleneck for real-world applications, especially for high power and high frequency devices. Similar to GaN/AlGaN interfaces, β-(AlxGa1-x)2O3/Ga2O3 heterogeneous structures have been used to form a high mobility two-dimensional electron gas (2DEG) where joule heating is localized. The thermal properties of β-(AlxGa1-x)2O3/Ga2O3 are the key for heat dissipation in these devices while they have not been studied before. This work reports the first measurement on thermal conductivity of β(Al0.1Ga0.9)2O3/Ga2O3 superlattices from 80 K to 480 K. Its thermal conductivity is significantly reduced (5.7 times reduction) at room temperature comparing with that of bulk Ga2O3. Additionally, the thermal conductivity of bulk Ga2O3 with (010) orientation is measured and found to be consistent with literature values regardless of Sn doping. We discuss the phonon scattering mechanism in these structures by calculating their inverse thermal diffusivity. By comparing the estimated thermal boundary conductance (TBC) of β-(Al0.1Ga0.9)2O3/Ga2O3 interfaces and Ga2O3 maximum TBC, we reveal that some phonons in the superlattices transmit through several interfaces before scattering with other phonons or structural imperfections. This study is not only important for Ga2O3 electronics applications especially for high power and high frequency applications, but also for the fundamental thermal science of phonon transport across interfaces and in superlattices. Copyright © 2019, The Authors. All rights reserved.

关键词： Phonons

Subspace-Based Suppression of Cortical Stimulation Artifacts

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Subspace-Based Suppression of Cortical Stimulation Artifacts

Annual International Conference of the IEEE engineering in Medicine and Biology Society

作者： Po. T. Wang Colin M. McCrimmon Payam Heydari An. H. Do Zoran Nenadic University of California Irvine Irvine CA US Medical Science Training Program UCI Department of Electrical Engineering and Computer Science UCI Department of Neurology UCI

Bi-directional brain-computer interfaces for the restoration of movement and sensation must simultaneously record neural signals and deliver cortical stimulation. This poses a challenge since stimulation artifacts can be orders of magnitude stronger than neural signals. In this article, we propose a novel subspace-based method for the removal of cortical electrical stimulation artifacts. We demonstrate the practical application of our approach on experimentally recorded electroencephalogram data, where artifacts were suppressed by as much as 30-40 dB. Our method is computationally simple, yet it achieves superior results to the state-of-the art methods.

关键词： Electroencephalography Integrated circuits Electrodes Signal to noise ratio Sensor arrays Covariance matrices Bidirectional control

Vibrational fingerprintings for chemical recognition of biominerals

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arXiv 2019年

作者： Calzolari, Arrigo Pavan, Barbara Curtarolo, Stefano Nardelli, Marco Buongiorno Fornari, Marco CNR-NANO Istituto Nanoscienze Centro S3 via Campi 213A Modena ITI-41125 Italy Department of Physics University of North Texas DentonTX76203 United States Department of Chemistry and Science Advanced Materials Program Central Michigan University Mt. PleasantMI48859 United States Materials Science Electrical Engineering Physics and Chemistry Duke University DurhamNC27708 United States Center for Materials Genomics Duke University DurhamNC27708 United States

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Identification of a functional point defect in SrTiO3

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Physical Review materials 2018年第6期2卷 060403(R)-060403(R)页

作者： Daesu Lee Hongwei Wang Brenton A. Noesges Thaddeus J. Asel Jinbo Pan Jung-Woo Lee Qimin Yan Leonard J. Brillson Xifan Wu Chang-Beom Eom Department of Materials Science and Engineering University of Wisconsin–Madison Madison Wisconsin 53706 USA Department of Physics Temple University Philadelphia Pennsylvania 19122 USA Department of Electrical and Computer Engineering and Department of Physics The Ohio State University Columbus Ohio 43210 USA

Unveiling both the presence and nature of point defects is one of the biggest challenges in condensed matter physics and materials science. Particularly in complex oxides, even a minute amount of unavoidable point defects could generate novel physical phenomena and functions, such as visible light emission and ferroelectricity, yet it remains elusive to clearly identify such point defects. Here, taking SrTiO3 as a model system, we show that iterative feedback among atomic-layer- and stoichiometry-controlled thin-film epitaxy, hybrid density functional theory, and high-resolution cathodoluminescence spectroscopy allows for the identification of a functional cationic defect, the Ti antisite (TiSr) defect. Our cathodoluminescence measurements reveal sub-band-gap luminescence, whose spectral fine structures show excellent quantitative agreement, as well as a one-to-one correspondence, with the theoretically predicted optical transitions from intrinsic point defects such as TiSr. Guided by the theory and spectroscopic results, we also control a cation stoichiometry, and it in turn results in good systematics in cathodoluminescence spectra. Not limited to the identification of TiSr, this approach allows for more reliable, self-consistent defect study, and provides critical insight into a microscopic picture of point defects in complex oxides.

关键词： Defects

Mid-infrared Optics Using Dielectrics with Refractive Indices Below Unity

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Physical Review Applied 2018年第3期10卷 034019-034019页

作者： Alireza Shahsafi Yuzhe Xiao Jad Salman Bradley S. Gundlach Chenghao Wan Patrick J. Roney Mikhail A. Kats Department of Electrical and Computer Engineering University of Wisconsin-Madison Madison WI 53706 USA Department of Materials Science and Engineering University of Wisconsin-Madison Madison WI 53706 USA Department of Physics University of Wisconsin - Madison Madison WI 53706 USA

Conventional transparent materials at optical frequencies have refractive-index values (n) greater than unity—most commonly between about 1 and 4. This paper explores optical phenomena made possible by using materials with refractive indices less than unity. We focus primarily on fused silica (SiO2), a well-studied dielectric with strong optical-phonon resonances in the mid infrared that result in a spectral region in which n

关键词： Classical optics Optical phonons Photonics Refraction Surface plasmon polariton Devices Dielectrics Infrared techniques