检索结果-内蒙古大学图书馆

Constraining primordial black holes using fast radio burst gravitational-lens interferometry with CHIME/FRB

Physical Review D 2022年第4期106卷 043017-043017页

作者： Calvin Leung Zarif Kader Kiyoshi W. Masui Matt Dobbs Daniele Michilli Juan Mena-Parra Ryan Mckinven Cherry Ng Kevin Bandura MIT Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge Massachusetts 02139 USA Department of Physics Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge Massachusetts 02139 USA Department of Physics McGill University 3600 rue University Montréal Quebec H3A 2T8 Canada McGill Space Institute McGill University 3550 rue University Montréal Quebec H3A 2A7 Canada Dunlap Institute for Astronomy & Astrophysics University of Toronto 50 St. George Street Toronto Ontario M5S 3H4 Canada Lane Department of Computer Science and Electrical Engineering 1220 Evansdale Drive PO Box 6109 Morgantown West Virginia 26506 USA Center for Gravitational Waves and Cosmology West Virginia University Chestnut Ridge Research Building Morgantown West Virginia 26505 USA

Fast radio bursts (FRBs) represent an exciting frontier in the study of gravitational lensing, due to their brightness, extragalactic nature, and the compact, coherent characteristics of their emission. In a companion work [Z. Kader and C. Leung, Phys. Rev. D 106, 043016 (2022).], we use a novel interferometric method to search for gravitationally lensed FRBs in the time domain using bursts detected by CHIME/FRB. There, we dechannelize and autocorrelate electric field data at a time resolution of 1.25 ns. This enables a search for FRBs whose emission is coherently deflected by gravitational lensing around a foreground compact object such as a primordial black hole (PBH). Here, we use our nondetection of lensed FRBs to place novel constraints on the PBH abundance outside the Local Group. We use a novel two-screen model to take into account decoherence from scattering screens in our constraints. Our constraints are subject to a single astrophysical model parameter—the effective distance between an FRB source and the scattering screen, for which we adopt a fiducial distance of 1 pc. We find that coherent FRB lensing is a sensitive probe of sub-solar mass compact objects. Having observed no lenses in 172 bursts from 114 independent sightlines through the cosmic web, we constrain the fraction of dark matter made of compact objects, such as PBHs, to be f≲0.8, if their masses are ∼10−3 M⊙.

关键词：

来源：评论

学校读者我要写书评

暂无评论

A quantum instruction set implemented on a superconducting quantum processor

arXiv

引用

arXiv 2020年

作者： Kjaergaard, M. Schwartz, M.E. Greene, A. Samach, G.O. Bengtsson, A. O'Keeffe, M. McNally, C.M. Braumüller, J. Kim, D.K. Krantz, P. Marvian, M. Melville, A. Niedzielski, B.M. Sung, Y. Winik, R. Yoder, J. Rosenberg, D. Obenland, K. Lloyd, S. Orlando, T.P. Marvian, I. Gustavsson, S. Oliver, W.D. Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory LexingtonMA02421 United States Microtechnology and Nanoscience Chalmers University of Technology GöteborgSE-412 96 Sweden Department of Mechanical Engineering Massachusetts Institute of Technology CambridgeMA02139 United States Departments of Physics & Electrical and Computer Engineering Duke University DurhamNC27708 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering & Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States Microtechnology and Nanoscience Chalmers University of Technology

A quantum algorithm consists of a sequence of operations and measurements applied to a quantum processor. To date, the instruction set which defines this sequence has been provided by a classical computer and passed via control hardware to the quantum processor. Here, we demonstrate the first experimental realization of a quantum instruction set, in which a fixed sequence of classically-defined gates perform an operation that is fully determined only by a quantum input to the fixed sequence. Specifically, we implement the density matrix exponentiation algorithm, which consumes N copies of the instruction state ρ to approximate the operation e−iρθ (θ an arbitrary angle). Our implementation relies on a 99.7% fidelity controlled-phase gate between two superconducting transmon qubits. We achieve an average algorithmic fidelity ≈ 0.9, independent of the setting of ρ, to circuit depth nearly 90. This new paradigm for quantum instructions has applications to resource-efficient protocols for validating entanglement spectra, principal component analysis of large quantum states, and universal quantum emulation. Copyright © 2020, The Authors. All rights reserved.

关键词： Quantum entanglement

来源：评论

学校读者我要写书评

暂无评论

High-time resolution search for compact objects using fast radio burst gravitational lens interferometry with CHIME/FRB

引用

Physical Review D 2022年第4期106卷 043016-043016页

作者： Zarif Kader Calvin Leung Matt Dobbs Kiyoshi W. Masui Daniele Michilli Juan Mena-Parra Ryan Mckinven Cherry Ng Kevin Bandura Department of Physics McGill University 3600 rue University Montréal Quebec H3A 2T8 Canada McGill Space Institute McGill University 3550 rue University Montréal Quebec H3A 2A7 Canada MIT Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge Massachusetts 02139 USA Department of Physics Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge Massachusetts 02139 USA Dunlap Institute for Astronomy & Astrophysics University of Toronto 50 St. George Street Toronto Ontario M5S 3H4 Canada Lane Department of Computer Science and Electrical Engineering 1220 Evansdale Drive PO Box 6109 Morgantown West Virginia 26506 USA Center for Gravitational Waves and Cosmology West Virginia University Chestnut Ridge Research Building Morgantown West Virginia 26505 USA

The gravitational field of compact objects, such as primordial black holes, can create multiple images of background sources. For transients such as fast radio bursts (FRBs), these multiple images can be resolved in the time domain. Under certain circumstances, these images not only have similar burst morphologies but are also phase-coherent at the electric field level. With a novel dechannelization algorithm and a matched filtering technique, we search for repeated copies of the same electric field waveform in observations of FRBs detected by the FRB backend of the Canadian Hydrogen Mapping Intensity Experiment (CHIME). An interference fringe from a coherent gravitational lensing signal will appear in the time-lag domain as a statistically significant peak in the time-lag autocorrelation function. We calibrate our statistical significance using telescope data containing no FRB signal. Our dataset consists of ∼100-ms long recordings of voltage data from 172 FRB events, dechannelized to 1.25-ns time resolution. This coherent search algorithm allows us to search for gravitational lensing signatures from compact objects in the mass range of 10−4–104 M⊙. After ruling out an anomalous candidate due to diffractive scintillation, we find no significant detections of gravitational lensing in the 172 FRB events that have been analyzed. In a companion work [C. Leung and Z. Kader, Phys. Rev. D 106, 043017 (2022).], we interpret the constraints on dark matter from this search.

关键词：

来源：评论

学校读者我要写书评

暂无评论

Between-ride routing for private transportation services

arXiv

引用

arXiv 2018年

作者： Schneider, Ian Kuan, Jun Jie Joseph Roozbehani, Mardavij Dahleh, Munther Department of Electrical Engineering & Computer Science MIT Laboratory for Information and Decision Systems MIT

Spurred by the growth of transportation network companies and increasing data capabilities, vehicle routing and ride-matching algorithms can improve the efficiency of private transportation services. However, existing routing solutions do not address where drivers should travel after dropping off a passenger and before receiving the next passenger ride request, i.e., during the between-ride period. We address this problem by developing an efficient algorithm to find the optimal policy for drivers between rides in order to maximize driver profits. We model the road network as a graph, and we show that the between-ride routing problem is equivalent to a stochastic shortest path problem, an infinite dynamic program with no discounting. We prove under reasonable assumptions that an optimal routing policy exists that avoids cycles;policies of this type can be efficiently found. We present an iterative approach to find an optimal routing policy. Our approach can account for various factors, including the frequency of passenger ride requests at different locations, traffic conditions, and surge pricing. We demonstrate the effectiveness of the approach by implementing it on road network data from Boston and New York City. Copyright © 2018, The Authors. All rights reserved.

关键词： Vehicle routing

来源：评论

学校读者我要写书评

暂无评论

engineering Framework for Optimizing Superconducting Qubit Designs

arXiv

引用

arXiv 2020年

作者： Yan, Fei Sung, Youngkyu Krantz, Philip Kamal, Archana Kim, David K. Yoder, Jonilyn L. Orlando, Terry P. Gustavsson, Simon Oliver, William D. Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory 244 Wood Street LexingtonMA02421 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen Guangdong518055 China Department of Physics and Applied Physics University of Massachusetts Lowell LowellMA01854 United States

Superconducting quantum technologies require qubit systems whose properties meet several often conflicting requirements, such as long coherence times and high anharmonicity. Here, we provide an engineering framework based on a generalized superconducting qubit model in the flux regime, which abstracts multiple circuit design parameters and thereby supports design optimization across multiple qubit properties. We experimentally investigate a special parameter regime which has both high anharmonicity (∼1 GHz) and long quantum coherence times (T1 =40−80 µs and T2Echo =2T1). Copyright © 2020, The Authors. All rights reserved.

关键词： Qubits

来源：评论

学校读者我要写书评

暂无评论

A Polariton-stabilized spin clock

arXiv

引用

arXiv 2020年

作者： Trusheim, Matthew E. Jacobs, Kurt Hoffman, Jonathan E. Fahey, Donald P. Braje, Danielle A. Englund, Dirk R. U.S. Army Research Laboratory Sensors and Electron Devices Directorate AdelphiMD20783 United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 77 Massachusetts Avenue CambridgeMA02139 United States Department of Physics University of Massachusetts at Boston BostonMA02125 United States MIT Lincoln Laboratory LexingtonMA02420 United States

Atom-like quantum systems in solids have been proposed as a compact alternative for atomic clocks, but realizing the potential of solid-state technology will requires an architecture design which overcomes traditional limitations such as magnetic and temperature-induced systematics. Here, we propose a solution to this problem: a ‘solid-state spin clock’ that hybridizes a microwave resonator with a magnetic-field-insensitive spin transition within the ground state of the diamond nitrogen-vacancy center. Detailed numerical and analytical modeling of this ‘polariton-stabilized’ spin clock (PSSC) indicates a potential fractional frequency instability below 10−13 at 1 second measurement time, assuming present-day experimental parameters. This stability would represent a significant improvement over the state-of-the-art in miniaturized atomic vapor clocks. Copyright © 2020, The Authors. All rights reserved.

关键词： Photons

来源：评论

学校读者我要写书评

暂无评论

Angular Dispersion Compensation Scheme for the Idler of Broadband Optical Parametric Amplifiers

Angular Dispersion Compensation Scheme for the Idler of Broa...

引用

Conference on Lasers and Electro-Optics (CLEO)

作者： Hüseyin Çankaya Giovanni Cirmi Peter Krogen Anne-Laure Calendron Yi Hua Benoit Debord Frédéric Gérome Fetah Benabid Franz X. Kärtner University of Hamburg Hamburg Germany Department of Physics Center for Free Electron Laser Science (CFEL) Deutsches Elektronen-Synchrotron (DESY) University of Hamburg Hamburg Germany The Hamburg Center for Ultrafast Imaging Hamburg Germany Department of Electrical Engineering and Computer Science Research Laboratory of Electronics Massachusetts Institute of Technology (MIT) Cambridge Massachusetts USA GPPMM Group Xlim Research Institute UMR 7252 CNRS University of Limoges Limoges France University of Limoges Limoges France

We demonstrate a technique for compensation of the idler angular chirp from an optical parametric amplifier in non-collinear geometry. This method enables generating broadband CEP-stable pulses for seeding high-energy... 详细信息

ISBN: (数字)9781943580767

ISBN: (纸本)9781728144184

关键词： Optical fiber amplifiers Nonlinear optics Optical amplifiers Stimulated emission Optical pumping

来源：评论

学校读者我要写书评

暂无评论

Regret Bounds and Regimes of Optimality for User-User and Item-Item Collaborative Filtering

Regret Bounds and Regimes of Optimality for User-User and It...

引用

Information Theory and Applications Workshop, ITA

作者： Guy Bresler Mina Karzand Department of Electrical Engineering and Computer Science MIT and a member of LIDS and IDSS

We consider an online model for recommendation systems, with each user being recommended an item at each time-step and providing `like' or `dislike' feedback. A latent variable model specifies the user preferences: both users and items are clustered into types . All users of a given type have identical preferences for the items, and similarly, items of a given type are either all liked or all disliked by a given user. The model captures structure in both the item and user spaces, and in this paper we assume that the type preference matrix is randomly generated. We describe two algorithms inspired by user-user and item-item collaborative filtering (CF), modified to explicitly make exploratory recommendations, and prove performance guarantees in terms of their expected regret. For two regimes of model parameters, with structure only in item space or only in user space, we prove information-theoretic lower bounds on regret that match our upper bounds up to logarithmic factors. Our analysis elucidates system operating regimes in which existing CF algorithms are nearly optimal.

关键词： Collaboration Motion pictures Prediction algorithms Analytical models electrical engineering computer science Clustering algorithms

来源：评论

学校读者我要写书评

暂无评论

BUDA-SAGE with self-supervised denoising enables fast, distortion-free, high-resolution T2, T2∗, para- And dia-magnetic susceptibility mapping

arXiv

引用

arXiv 2021年

作者： Zhang, Zijing Wang, Long Cho, Jaejin Liao, Congyu Shin, Hyeong-Geol Cao, Xiaozhi Lee, Jongho Xu, Jinmin Zhang, Tao Ye, Huihui Setsompop, Kawin Liu, Huafeng Bilgic, Ber-Kin State Key Laboratory of Modern Optical Instrumentation College of Optical Science and Engi-neering Zhejiang University Zhejiang Hangzhou China Athinoula A. Martinos Center for Biomedical Imaging Massachusetts General Hospital CharlestownMA United States Subtle Medical Inc Menlo ParkCA United States Department of Radiology Harvard Medical School CharlestownMA United States Radiological Sciences Laboratory Stanford University StanfordCA United States Department of Electrical and Computer Engineering Seoul National University Seoul Korea Republic of Harvard-MIT Health Sciences and Technology Massachusetts Institute of Technology Cam-bridgeMA United States

Purpose: To rapidly obtain high resolution T2, T2∗ and quantitative susceptibility mapping (QSM) source separation maps with whole-brain coverage and high geometric fidelity. Methods: We propose Blip Up-Down Acquisition for Spin And Gradient Echo imaging (BUDA-SAGE), an efficient echo-planar imaging (EPI) sequence for quantitative mapping. The acquisition includes multiple T2∗-, T2'- and T2-weighted contrasts. We alternate the phase-encoding polarities across the interleaved shots in this multi-shot navigator-free acquisition. A field map estimated from interim reconstructions was incorporated into the joint multi-shot EPI reconstruction with a structured low rank constraint (BUDA reconstruction) to eliminate geometric distortion. A self-supervised MR-Self2Self (MR-S2S) neural network (NN) was utilized to perform denoising after BUDA reconstruction to boost SNR. Employing Slider encoding allowed us to reach 1 mm iso-tropic resolution by performing super-resolution reconstruction on BUDA-SAGE volumes ac-quired with 2 mm slice thickness. Quantitative T2(=1/R2) and T2∗ (=1/R2∗) maps were obtained using Bloch dictionary matching on the reconstructed echoes. QSM was estimated using nonlinear dipole inversion (NDI) on the gradient echoes. Starting from the estimated R2and R2∗ maps, R2' information was derived and used in source separation QSM reconstruction, which provided addi-tional para- and dia-magnetic susceptibility maps. Results: In vivo results demonstrate the ability of BUDA-SAGE to provide whole-brain, distor-tion-free, high-resolution multi-contrast images and quantitative T2and T2∗ maps, as well as yield-ing para- and dia-magnetic susceptibility maps. Derived quantitative maps showed comparable values to conventional mapping methods in phantom and in vivo measurements. Conclusion: BUDA-SAGE acquisition with self-supervised denoising and Slider encoding ena-bles rapid, distortion-free, whole-brain T2, T2∗ mapping at 1 mm isotropic resolution in 90 seconds. © 20

关键词： Mapping

来源：评论

学校读者我要写书评

暂无评论

Corrigendum to "Placental MRI: Effect of maternal position and uterine contractions on placental BOLD MRI measurements" [Placenta 95 (2020) 69-77]

引用

Placenta 2020年 100卷 171-172页

作者： Esra Abaci Turk S Mazdak Abulnaga Jie Luo Jeffrey N Stout Henry A Feldman Ata Turk Borjan Gagoski Lawrence L Wald Elfar Adalsteinsson Drucilla J Roberts Carolina Bibbo Julian N Robinson Polina Golland P Ellen Grant William H Barth Fetal-Neonatal Neuroimaging & Developmental Science Center Boston Children's Hospital Harvard Medical School Boston MA USA. Electronic address: esra.abaciturk@childrens.harvard.edu. Computer Science and Artificial Intelligence Laboratory (CSAIL) Massachusetts Institute of Technology Cambridge MA USA. Fetal-Neonatal Neuroimaging & Developmental Science Center Boston Children's Hospital Harvard Medical School Boston MA USA School of Biomedical Engineering Shanghai Jiao Tong University Shanghai China. Fetal-Neonatal Neuroimaging & Developmental Science Center Boston Children's Hospital Harvard Medical School Boston MA USA. Institutional Centers for Clinical and Translational Research Boston Children's Hospital Harvard Medical School Boston MA USA. Electrical Computer Engineering Department Boston University Boston MA USA. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA USA Radiology Harvard Medical School Boston MA United States Athinoula A. Martinos Center for Biomedical Imaging Massachusetts General Hospital Charlestown MA United States. Harvard-MIT Health Sciences and Technology Massachusetts Institute of Technology Cambridge MA USA Institute for Medical Engineering and Science Massachusetts Institute of Technology Cambridge MA USA. Department of Pathology Massachusetts General Hospital Boston MA USA. Maternal Fetal Medicine Brigham and Women's Hospital Boston MA USA. Computer Science and Artificial Intelligence Laboratory (CSAIL) Massachusetts Institute of Technology Cambridge MA USA Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA USA. Maternal-Fetal Medicine Obstetrics and Gynecology Massachusetts General Hospital Boston MA USA.

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：