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A Detection of Cosmological 21 cm Emission from CHIME in Cross-correlation with eBOSS Measurements of the Lyman-α Forest

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arXiv 2023年

作者： Amiri, Mandana Bandura, Kevin Chakraborty, Arnab Dobbs, Matt Fandino, Mateus Foreman, Simon Gan, Hyoyin Halpern, Mark Hill, Alex S. Hinshaw, Gary Höfer, Carolin Landecker, T.L. Li, Zack Maceachern, Joshua Masui, Kiyoshi Mena-Parra, Juan Milutinovic, Nikola Mirhosseini, Arash Newburgh, Laura Ordog, Anna Paul, Sourabh Pen, Ue-Li Pinsonneault-Marotte, Tristan Reda, Alex Shaw, J. Richard Siegel, Seth R. Vanderlinde, Keith Wang, Haochen Wiebe, D.V. Wulf, Dallas Department of Physics and Astronomy University of British Columbia VancouverBC Canada Department of Computer Science and Electrical Engineering West Virginia University MorgantownWV United States Center for Gravitational Waves and Cosmology West Virginia University MorgantownWV United States Department of Physics McGill University MontrealQC Canada Trottier Space Institute McGill University MontrealQC Canada Department of Physical Sciences Thompson Rivers University KamloopsBC Canada Department of Physics Arizona State University TempeAZ United States Department of Computer Science Math Physics and Statistics University of British Columbia-Okanagan KelownaBC Canada Dominion Radio Astrophysical Observatory Herzberg Astronomy & Astrophysics Research Centre National Research Council Canada PentictonBC Canada Kapteyn Astronomical Institute University of Groningen Groningen Netherlands Canadian Institute for Theoretical Astrophysics TorontoON Canada MIT Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology CambridgeMA United States Department of Physics Massachusetts Institute of Technology CambridgeMA United States Dunlap Institute for Astronomy and Astrophysics University of Toronto TorontoON Canada David A. Dunlap Department of Astronomy & Astrophysics University of Toronto TorontoON Canada Department of Physics Yale University New HavenCT United States Perimeter Institute for Theoretical Physics WaterlooON Canada

We report the detection of 21 cm emission at an average redshift z¯ = 2.3 in the cross-correlation of data from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) with measurements of the Lyman-α forest from eBOSS. Data collected by CHIME over 88 days in the 400 − 500 MHz frequency band (1.8 0.13 Mpc−1 at the average redshift. Line-of-sight spectra to the eBOSS background quasar locations are extracted from the CHIME maps and combined with the Lyman-α forest flux transmission spectra to estimate the 21 cm-Lyman-α cross-correlation function. Fitting a simulation-derived template function to this measurement results in a 9σ detection significance. The coherent accumulation of the signal through cross-correlation is sufficient to enable a detection despite excess variance from foreground residuals ∼ 6 − 10 times brighter than the expected thermal noise level in the correlation function. These results are the highest-redshift measurement of 21 cm emission to date, and set the stage for future 21 cm intensity mapping analyses at z > 1.8. © 2023, CC BY.

关键词： Mapping

Analysis and Optimization of Aperture Design in Computational Imaging

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Analysis and Optimization of Aperture Design in Computationa...

International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： Adam Yedidia Christos Thrampoulidis Gregory Wornell Department of Electrical Engineering and Computer Science MIT

ISBN: (纸本)9781538646595

There is growing interest in the use of coded aperture imaging systems for a variety of applications. Using an analysis framework based on mutual information, we examine the fundamental limits of such systems-and the associated optimum aperture coding-under simple but meaningful propagation and sensor models. Among other results, we show that when SNR is high and thermal noise dominates shot noise, spectrally-flat masks, which have 50% transmissivity, are optimal, but that when shot noise dominates thermal noise, randomly generated masks with lower transmissivity offer greater performance. We also provide comparisons to classical pinhole and lens-based cameras.

关键词： Apertures Lenses Mutual information Thermal noise Cameras Artificial neural networks

Optimal Transport on Discrete Domains

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arXiv 2018年

作者： Solomon, Justin MIT Department of Electrical Engineering and Computer Science

Inspired by the matching of supply to demand in logistical problems, the optimal transport (or Monge–Kantorovich) problem involves the matching of probability distributions defined over a geometric domain such as a surface or manifold. In its most obvious discretization, optimal transport becomes a large-scale linear program, which typically is infeasible to solve efficiently on triangle meshes, graphs, point clouds, and other domains encountered in graphics and machine learning. Recent breakthroughs in numerical optimal transport, however, enable scalability to orders-of-magnitude larger problems, solvable in a fraction of a second. Here, we discuss advances in numerical optimal transport that leverage understanding of both discrete and smooth aspects of the problem. State-of-the-art techniques in discrete optimal transport combine insight from partial differential equations (PDE) with convex analysis to reformulate, discretize, and optimize transportation problems. The end result is a set of theoretically-justified models suitable for domains with thousands or millions of vertices. Since numerical optimal transport is a relatively new discipline, special emphasis is placed on identifying and explaining open problems in need of mathematical insight and additional research. Copyright © 2018, The Authors. All rights reserved.

关键词： Probability distributions

Characterizing and optimizing qubit coherence based on SQUID geometry

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arXiv 2020年

作者： Braumuller, Jochen Ding, Leon Vepsalainen, Antti Sung, Youngkyu Kjaergaard, Morten Menke, Tim Winik, Roni Kim, David Niedzielski, Bethany M. Melville, Alexander Yoder, Jonilyn L. Hirjibehedin, Cyrus F. Orlando, Terry P. Gustavsson, Simon Oliver, William D. Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory LexingtonMA02421 United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States

The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/f flux noise. To understand its origin and find ways to minimize its impact, we systematically study flux noise amplitudes in more than 50 flux qubits with varied SQUID geometry parameters and compare our results to a microscopic model of magnetic spin defects located at the interfaces surrounding the SQUID loops. Our data are in agreement with an extension of the previously proposed model, based on numerical simulations of the current distribution in the investigated SQUIDs. Our results and detailed model provide a guide for minimizing the flux noise susceptibility in future circuits. Copyright © 2020, The Authors. All rights reserved.

关键词： Qubits

The effect of the pauli spin matrices on the quantum lattice algorithm for maxwell equations in inhomogeneous media

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arXiv 2020年

作者： Vahala, George Vahala, Linda Soe, Min Ram, Abhay K. Department of Physics William & Mary WilliamsburgVA23185 United States Department of Electrical & Computer Engineering Old Dominion University NorfolkVA12319 United States Department of Mathematics and Physical Sciences Rogers State University ClaremoreOK74017 United States Plasma Science and Fusion Center MIT CambridgeMA 02139 United Kingdom

A quantum lattice algorithm (QLA) is developed for the solution of Maxwell equations in scalar dielectric media using the Riemann-Silberstein representation. For x-dependent and y-dependent inhomogeneities, the corresponding QLA requries 8 qubits/spatial lattice site. This is because the corresponding Pauli spin matrices have off-diagonal components which permit the collisional entanglement of two qubits. However, z-dependent inhomogeneities require a QLA with 16 qubits/lattice site since the Pauli spin matrix σz is diagonal. QLA simulations are performed for the time evolution of an initial electromagnetic pulse propagating normally to a boundary layer region joining two media of different refractive index. There is excellent agreement between all three representations, as well as very good agreement with nearly all the standard plane wave boundary condition results for reflection and transmission off a dielectric discontinuity. In the QLA simulation, no boundary conditions are imposed at the continuous, but sharply increasing, boundary layer. © 2020, CC-BY.

关键词： Maxwell equations

Microwave package design for superconducting quantum processors

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arXiv 2020年

作者： Huang, Sihao Lienhard, Benjamin Calusine, Greg Vepsäläinen, Antti Braumüller, Jochen Kim, David K. Melville, Alexander J. Niedzielski, Bethany M. Yoder, Jonilyn L. Kannan, Bharath Orlando, Terry P. Gustavsson, Simon Oliver, William D. Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory LexingtonMA02421 United States

Solid-state qubits with transition frequencies in the microwave regime, such as superconducting qubits, are at the forefront of quantum information processing. However, high-fidelity, simultaneous control of superconducting qubits at even a moderate scale remains a challenge, partly due to the complexities of packaging these devices. Here, we present an approach to microwave package design focusing on material choices, signal line engineering, and spurious mode suppression. We describe design guidelines validated using simulations and measurements used to develop a 24-port microwave package. Analyzing the qubit environment reveals no spurious modes up to 11 GHz. The material and geometric design choices enable the package to support qubits with lifetimes exceeding 350 µs. The microwave package design guidelines presented here address many issues relevant for near-term quantum processors. Copyright © 2020, The Authors. All rights reserved.

关键词： Quantum optics

Realization of high-fidelity CZ and ZZ-free iSWAP gates with a tunable coupler

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arXiv 2020年

作者： Sung, Youngkyu Ding, Leon Braumüller, Jochen Vepsäläinen, Antti Kannan, Bharath Kjaergaard, Morten Greene, Ami Samach, Gabriel O. McNally, Chris Kim, David Melville, Alexander Niedzielski, Bethany M. Schwartz, Mollie E. 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 Department of Physics Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory LexingtonMA02421 United States

High-fidelity two-qubit gates at scale are a key requirement to realize the full promise of quantum computation and simulation. The advent and use of coupler elements to tunably control two-qubit interactions has improved operational fidelity in many-qubit systems by reducing parasitic coupling and frequency crowding issues. Nonetheless, two-qubit gate errors still limit the capability of near-term quantum applications. The reason, in part, is the existing framework for tunable couplers based on the dispersive approximation does not fully incorporate three-body multi-level dynamics, which is essential for addressing coherent leakage to the coupler and parasitic longitudinal (ZZ) interactions during two-qubit gates. Here, we present a systematic approach that goes beyond the dispersive approximation to exploit the engineered level structure of the coupler and optimize its control. Using this approach, we experimentally demonstrate CZ and ZZ-free iSWAP gates with two-qubit interaction fidelities of 99.76 ± 0.07% and 99.87 ± 0.23%, respectively, which are close to their T1 limits. Copyright © 2020, The Authors. All rights reserved.

关键词： Logic gates

Extreme classification in log memory using count-min sketch: A case study of amazon search with 50m products

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arXiv 2019年

作者： Medini, Tharun Huang, Qixuan Wang, Yiqiu Mohan, Vijai Shrivastava, Anshumali Electrical and Computer Engineering Rice University HoustonTX77005 United States Computer Science Rice University HoustonTX77005 United States Computer Science MIT CambridgeMA02139 United States Amazon Search Palo AltoCA94301

In the last decade, it has been shown that many hard AI tasks, especially in NLP, can be naturally modeled as extreme classification problems leading to improved precision. However, such models are prohibitively expensive to train due to the memory blow-up in the last layer. For example, a reasonable softmax layer for the dataset of interest in this paper can easily reach well beyond 100 billion parameters (> 400 GB memory). To alleviate this problem, we present Merged-Average Classifiers via Hashing (MACH), a generic K-classification algorithm where memory provably scales at O(log K) without any strong assumption on the classes. MACH is subtly a count-min sketch structure in disguise, which uses universal hashing to reduce classification with a large number of classes to few embarrassingly parallel and independent classification tasks with a small (constant) number of classes. MACH naturally provides a technique for zero communication model parallelism. We experiment with 6 datasets;some multiclass and some multilabel, and show consistent improvement over respective state-of-the-art baselines. In particular, we train an end-to-end deep classifier on a private product search dataset sampled from Amazon Search Engine with 70 million queries and 49.46 million products. MACH outperforms, by a significant margin, the state-of-the-art extreme classification models deployed on commercial search engines: Parabel and dense embedding models. Our largest model has 6.4 billion parameters and trains in less than 35 hours on a single p3.16x machine. Our training times are 7-10x faster, and our memory footprints are 2-4x smaller than the best baselines. This training time is also significantly lower than the one reported by Google's mixture of experts (MoE) language model on a comparable model size and hardware. Copyright © 2019, The Authors. All rights reserved.

关键词： Search engines

A VLBI Software Correlator for Fast Radio Transients

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arXiv 2024年

作者： Leung, Calvin Andrew, Shion Masui, Kiyoshi W. Brar, Charanjot Cassanelli, Tomas Chatterjee, Shami Kaspi, Victoria Khairy, Kholoud Lanman, Adam E. Lazda, Mattias Mena-Parra, Juan Noble, Gavin Pearlman, Aaron B. Rahman, Mubdi Sanghavi, Pranav Shah, Vishwangi Department of Astronomy University of California Berkeley BerkeleyCA94720 United States MIT Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology 77 Massachusetts Ave CambridgeMA02139 United States Department of Physics Massachusetts Institute of Technology 77 Massachusetts Ave CambridgeMA02139 United States United States Department of Physics McGill University 3600 rue University MontréalQCH3A 2T8 Canada Trottier Space Institute McGill University 3550 rue University MontréalQCH3A 2A7 Canada Department of Electrical Engineering Universidad de Chile Av. Tupper 2007 Santiago8370451 Chile Cornell Center for Astrophysics and Planetary Science Cornell University IthacaNY14853 United States Lane Department of Computer Science and Electrical Engineering 1220 Evansdale Drive PO Box 6109 MorgantownWV26506 United States Center for Gravitational Waves and Cosmology West Virginia University Chestnut Ridge Research Building MorgantownWV26505 United States Dunlap Institute for Astronomy & Astrophysics University of Toronto 50 St. George Street TorontoONM5S 3H4 Canada David A. Dunlap Department of Astronomy & Astrophysics University of Toronto 50 St. George Street TorontoONM5S 3H4 Canada McGill Space Institute Canada FRQNT Postdoctoral Fellow Canada Sidrat Research 124 Merton Street Suite 507 TorontoONM4S 2Z2 Canada Department of Physics Yale University New HavenCT06520 United States

One major goal in fast radio burst science is to detect fast radio bursts (FRBs) over a wide field of view without sacrificing the angular resolution required to pinpoint them to their host galaxies. Wide-field detection and localization capabilities have already been demonstrated using connected-element interferometry;the CHIME/FRB Outriggers project will push this further using widefield cylindrical telescopes as widefield outriggers for very long baseline interferometry (VLBI). This paper describes an offline VLBI software correlator written in Python for the CHIME/FRB Outriggers project. It includes features well-suited to modern widefield instruments like multibeaming/multiple phase center correlation, pulse gating including coherent dedispersion, and a novel correlation algorithm based on the quadratic estimator formalism. This algorithm mitigates sensitivity loss which arises in instruments where the windowing and channelization is done outside the VLBI correlator at each station, which accounts for a 30 percent sensitivity drop away from the phase center. Our correlation algorithm recovers this sensitivity on both simulated and real data. As an end to end check of our software, we have written a preliminary pipeline for VLBI calibration and single-pulse localization, which we use in Lanman et al. (2024) to verify the astrometric accuracy of the CHIME/FRB Outriggers array. Copyright © 2024, The Authors. All rights reserved.

关键词： Radio astronomy