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arXiv 2023年

作者： Zaletel, Michael P. Lukin, Mikhail Monroe, Christopher Nayak, Chetan Wilczek, Frank Yao, Norman Y. Department of Physics University of California BerkeleyCA94720 United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Physics Haarvard University CambridgeMA02138 United States Duke Quantum Center Department of Electrical and Computer Engineering Department of Physics Duke University DurhamNC27701 United States Microsoft Quantum University of California Station Q Santa BarbaraCA93106 United States Department of Physics University of California Santa BarbaraCA93106 United States Center for Theoretical Physics MIT CambridgeMA02139 United States T. D. Lee Institute Wilczek Quantum Center SJTU Shanghai China Arizona State University TempeAZ United States Stockholm University Stockholm Sweden

The spontaneous breaking of time translation symmetry has led to the discovery of a new phase of matter – the discrete time crystal. Discrete time crystals exhibit rigid subharmonic oscillations, which result from a combination of many-body interactions, collective synchronization, and ergodicity breaking. This Colloquium reviews recent theoretical and experimental advances in the study of quantum and classical discrete time crystals. We focus on the breaking of ergodicity as the key to discrete time crystals and the delaying of ergodicity as the source of numerous phenomena that share many of the properties of discrete time crystals, including the AC Josephson effect, coupled map lattices, and Faraday waves. Theoretically, there exists a diverse array of strategies to stabilize time crystalline order in both closed and open systems, ranging from localization and prethermalization to dissipation and error correction. Experimentally, many-body quantum simulators provide a natural platform for investigating signatures of time crystalline order;recent work utilizing trapped ions, solid-state spin systems, and superconducting qubits will be reviewed. Finally, this Colloquium concludes by describing outstanding challenges in the field and a vision for new directions on both the experimental and theoretical fronts. Copyright © 2023, The Authors. All rights reserved.

关键词： Quantum theory

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Time-efficient, High Resolution 3T Whole Brain Quantitative Relaxometry using 3D-QALAS with Wave-CAIPI Readouts

arXiv

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arXiv 2022年

作者： Cho, Jaejin Gagoski, Borjan Kim, Tae Hyung Wang, Fuyixue Splitthoff, Daniel Nico Lo, Wei-Ching Liu, Wei Polak, Daniel Cauley, Stephen Setsompop, Kawin Grant, P. Ellen Bilgic, Berkin Athinoula A. Martinos Center for Biomedical Imaging Massachusetts General Hospital CharlestownMA United States Department of Radiology Harvard Medical School BostonMA United States Fetal-Neonatal Neuroimaging & Developmental Science Center Boston Children’s Hospital BostonMA United States Department of Computer Engineering Hongik University Seoul Korea Republic of Siemens Healthcare GmbH Erlangen Germany Siemens Medical Solutions USA Inc. CharlestownMA United States Siemens Shenzhen Magnetic Resonance Ltd Shenzhen China Department of Electrical Engineering Stanford University StanfordCA United States Department of Radiology Stanford University StanfordCA United States Harvard/MIT Health Sciences and Technology CambridgeMA United States

Purpose: Volumetric, high-resolution, quantitative mapping of brain tissue relaxation properties is hindered by long acquisition times and signal-to-noise (SNR) challenges. This study, for the first time, combines the time-efficient wave-CAIPI readouts into the 3D-quantification using an interleaved Look-Locker acquisition sequence with a T2 preparation pulse (3D-QALAS) acquisition scheme, enabling full brain quantitative T1, T2 and proton density (PD) maps at 1.15 mm3 isotropic voxels in only 3 minutes. Methods: Wave-CAIPI readouts were embedded in the standard 3D-QALAS encoding scheme, enabling full brain quantitative parameter maps (T1, T2, and PD) at acceleration factors of R=3x2 with minimum SNR loss due to g-factor penalties. The quantitative parameter maps were estimated using a dictionary-based mapping algorithm incorporating inversion efficiency and B1 field inhomogeneity. The quantitative maps using the accelerated protocol were quantitatively compared against those obtained from conventional 3D-QALAS sequence using GRAPPA acceleration of R=2 in the ISMRM NIST phantom, and ten healthy volunteers. Results: When tested in both the ISMRM/NIST phantom and ten healthy volunteers, the quantitative maps using the accelerated protocol showed excellent agreement against those obtained from conventional 3D-QALAS at RGRAPPA=2. Conclusion: 3D-QALAS enhanced with wave-CAIPI readouts enables time-efficient, full brain quantitative T1, T2, and PD mapping at 1.15 mm3 in 3 minutes at R=3x2 acceleration. When tested on the NIST phantom and ten healthy volunteers, the quantitative maps obtained from the accelerated wave-CAIPI 3D-QALAS protocol showed very similar values to those obtained from the standard 3D-QALAS (R=2) protocol, alluding to the robustness and reliability of the proposed methods. Copyright © 2022, The Authors. All rights reserved.

关键词： Phantoms

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Why botnets work: Distributed brute-force attacks need no synchronization

Why botnets work: Distributed brute-force attacks need no sy...

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作者： Salamatian, Salman Huleihel, Wasim Beirami, Ahmad Cohen, Asaf Medard, Muriel Department of Electrical Engineering and Computer Science MIT CambridgeMA02139 United States Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering-Systems Tel-Aviv University Tel-Aviv6997801 Israel EA Digital Platform-Data and AI Electronic Arts Redwood CityCA94065 United States Department of Electrical Engineering Ben-Gurion University of the Negev Beersheba8410501 Israel

In September 2017, the McAfee Labs quarterly report estimated that brute-force attacks represent 20% of total network attacks, making them the most prevalent type of attack ex-aequo with browser-based vulnerabilities. These attacks have sometimes catastrophic consequences, and understanding their fundamental limits may play an important role in the risk assessment of password-secured systems and in the design of better security protocols. While some solutions exist to prevent online brute-force attacks that arise from one single IP address, attacks performed by botnets are more challenging. In this paper, we analyze these distributed attacks by using a simplified model. Our aim is to understand the impact of distribution and asynchronization on the overall computational effort necessary to breach a system. Our result is based on guesswork, a measure of the number of queries (guesses) before a correct sequence, such as a password, is found in an optimal attack. Guesswork is a direct surrogate for time and computational effort of guessing a sequence from a set of sequences with the associated likelihoods. We model the lack of synchronization by a worst-case optimization in which the queries made by multiple adversarial agents are received in the worst possible order for the adversary, resulting in a min-max formulation. We show that, even without synchronization, and for sequences of growing length, the asymptotic optimal performance is achievable by using randomized guesses drawn from an appropriate distribution. Therefore, randomization is key for the distributed asynchronous attacks. In other words, asynchronous guessers can asymptotically perform brute-force attacks as efficiently as synchronized guessers. © 2019 IEEE.

关键词： Botnet

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Lindblad Tomography of a Superconducting Quantum Processor

arXiv

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arXiv 2021年

作者： Samach, Gabriel O. Greene, Ami Borregaard, Johannes Christandl, Matthias Barreto, Joseph Kim, David K. McNally, Christopher M. Melville, Alexander Niedzielski, Bethany M. Sung, Youngkyu Rosenberg, Danna Schwartz, Mollie E. Yoder, Jonilyn L. Orlando, Terry P. Wang, Joel I-Jan Gustavsson, Simon Kjaergaard, Morten Oliver, William D. Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States MIT Lincoln Laboratory LexingtonMA02421 United States Qutech and Kavli Institute of Nanoscience Delft University of Technology Delft Netherlands Department of Mathematical Sciences University of Copenhagen Copenhagen Denmark Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen Denmark Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States

As progress is made towards the first generation of error-corrected quantum computers, robust characterization and validation protocols are required to assess the noise environments of physical quantum processors. While standard coherence metrics and characterization protocols such as T1 and T2, process tomography, and randomized benchmarking are now ubiquitous, these techniques provide only partial information about the dynamic multi-qubit loss channels responsible for processor errors, which can be described more fully by a Lindblad operator in the master equation formalism. Here, we introduce and experimentally demonstrate Lindblad tomography, a hardware-agnostic characterization protocol for tomographically reconstructing the Hamiltonian and Lindblad operators of a quantum noise environment from an ensemble of time-domain measurements. Performing Lindblad tomography on a small superconducting quantum processor, we show that this technique naturally builds on standard process tomography and T1/T2 measurement protocols, characterizes and accounts for state-preparation and measurement (SPAM) errors, and allows one to place bounds on the fit to a Markovian model Comparing the results of single- and two-qubit measurements on a superconducting quantum processor, we demonstrate that Lindblad tomography can also be used to identify and quantify sources of crosstalk on quantum processors, such as the presence of always-on qubit-qubit interactions. Copyright © 2021, The Authors. All rights reserved.

关键词： Tomography

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Calibration of flux crosstalk in large-scale flux-tunable superconducting quantum circuits

arXiv

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arXiv 2021年

作者： Dai, Xi Tennant, D.M. Trappen, R. Martinez, A.J. Melanson, D. Yurtalan, M.A. Tang, Y. Novikov, S. Grover, J.A. Disseler, S.M. Basham, J.I. Das, R. Kim, D.K. Melville, A.J. Niedzielski, B.M. Weber, S.J. Yoder, J.L. Lidar, D.A. Lupascu, A. Institute for Quantum Computing Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada Northrop Grumman Corporation LinthicumMD21090 United States MIT Lincoln Laboratory 244 Wood Street LexingtonMA02421 United States Departments of Electrical & Computer Engineering Chemistry and Physics Center for Quantum Information Science & Technology University of Southern California Los AngelesCA90089 United States Waterloo Institute for Nanotechnology University of Waterloo WaterlooONN2L 3G1 Canada

Magnetic flux tunability is an essential feature in most approaches to quantum computing based on superconducting qubits. Independent control of the fluxes in multiple loops is hampered by crosstalk. Calibrating flux crosstalk becomes a challenging task when the circuit elements interact strongly. We present a novel approach to flux crosstalk calibration, which is circuit model independent and relies on an iterative process to gradually improve calibration accuracy. This method allows us to reduce errors due to the inductive coupling between loops. The calibration procedure is automated and implemented on devices consisting of tunable flux qubits and couplers with up to 27 control loops. We devise a method to characterize the calibration error, which is used to show that the errors of the measured crosstalk coefficients are all below 0.17%. Copyright © 2021, The Authors. All rights reserved.

关键词： Crosstalk

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Nonexpansive piecewise constant hybrid systems are conservative

arXiv

引用

arXiv 2019年

作者： Sharifnassab, Arsalan Tsitsiklis, John N. Golestani, S. Jamaloddin Department of Electrical Engineering Sharif University of Technology Tehran Iran Laboratory for Information and Decision Systems Electrical Engineering and Computer Science Department MIT CambridgeMA02139 United States

Consider a partition of Rn into finitely many polyhedral regions Di and associated drift vectors µi ∈ Rn. We study "hybrid" dynamical systems whose trajectories have a constant drift, x = µi, whenever x is in the interior of the ith region Di, and behave consistently on the boundary between different regions. Our main result asserts that if such a system is nonexpansive (i.e., if the Euclidean distance between any pair of trajectories is a nonincreasing function of time), then the system must be conservative, i.e., its trajectories are the same as the trajectories of the negative subgradient flow associated with a potential function. Furthermore, this potential function is necessarily convex, and is linear on each of the regions Di. We actually establish a more general version of this result, by making seemingly weaker assumptions on the dynamical system of interest. Copyright © 2019, The Authors. All rights reserved.

关键词： Piecewise linear techniques

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Comparison of Dielectric Loss in Titanium Nitride and Aluminum Superconducting Resonators

arXiv

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arXiv 2020年

作者： Melville, A. Calusine, G. Woods, W. Serniak, K. Golden, E. Niedzielski, B.M. Kim, D.K. Sevi, A. Yoder, J.L. Dauler, E.A. Oliver, W.D. MIT Lincoln Laboratory 244 Wood Street LexingtonMA02421 United States Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Electrical Engineering & Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States

Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide (CPW) resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region’s contribution to resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal-air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric (HF) etch, and find that it reduced losses from the substrate-air interface, thereby improving the quality factor. Copyright © 2020, The Authors. All rights reserved.

关键词： Dielectric devices

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Author Correction: Distinct chemical environments in biomolecular condensates

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Nature chemical biology 2023年第12期19卷 1561页

作者： Henry R Kilgore Peter G Mikhael Kalon J Overholt Ann Boija Nancy M Hannett Catherine Van Dongen Tong Ihn Lee Young-Tae Chang Regina Barzilay Richard A Young Whitehead Institute for Biomedical Research Cambridge MA USA. hkilgore@wi.mit.edu. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA USA. Jameel Clinic Massachusetts Institute of Technology Cambridge MA USA. Whitehead Institute for Biomedical Research Cambridge MA USA. Department of Biological Engineering Massachusetts Institute of Technology Cambridge MA USA. Department of Chemistry Pohang University of Science and Technology Pohang Republic of Korea. Whitehead Institute for Biomedical Research Cambridge MA USA. young@wi.mit.edu. Department of Biology Massachusetts Institute of Technology Cambridge MA USA. young@wi.mit.edu.

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Development of Quantum Interconnects (QuICs) for Next-Generation Information Technologies

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PRX Quantum 2021年第1期2卷 017002-017002页

作者： David Awschalom Karl K. Berggren Hannes Bernien Sunil Bhave Lincoln D. Carr Paul Davids Sophia E. Economou Dirk Englund Andrei Faraon Martin Fejer Saikat Guha Martin V. Gustafsson Evelyn Hu Liang Jiang Jungsang Kim Boris Korzh Prem Kumar Paul G. Kwiat Marko Lončar Mikhail D. Lukin David A.B. Miller Christopher Monroe Sae Woo Nam Prineha Narang Jason S. Orcutt Michael G. Raymer Amir H. Safavi-Naeini Maria Spiropulu Kartik Srinivasan Shuo Sun Jelena Vučković Edo Waks Ronald Walsworth Andrew M. Weiner Zheshen Zhang Pritzker School of Molecular Engineering University of Chicago Chicago Illinois 60637 USA Department of Electrical Engineering and Computer Science MIT Cambridge Massachusetts 02139 USA School of Electrical and Computer Engineering Purdue University West Lafayette Indiana 47907 USA Department of Physics Colorado School of Mines 1500 Illinois Street Golden Colorado 80401 USA Photonic & Phononic Microsystems Sandia National Laboratory Albuquerque New Mexico 87185 USA Department of Physics Virginia Tech Blacksburg Virginia 24061 USA T .J. Watson Laboratory of Applied Physics California Institute of Technology Pasadena California 91125 USA Kavli Nanoscience Institute California Institute of Technology Pasadena California 91125 USA E.L. Ginzton Laboratory Stanford University Stanford California 94305 USA College of Optical Sciences The University of Arizona Tucson Arizona 85721 USA Department of Electrical and Computer Engineering The University of Arizona Tucson Arizona 85721 USA Department of Applied Mathematics The University of Arizona Tucson Arizona 85721 USA Raytheon BBN Technologies Cambridge Massachusetts 02138 USA John A. Paulson School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA Harvard Quantum Initiative (HQI) Harvard University Cambridge Massachusetts 02138 USA Department of Electrical and Computer Engineering Duke University Durham North Carolina 27708 USA IonQ Inc. College Park Maryland 20740 USA Jet Propulsion Laboratory California Institute of Technology Pasadena California 91109 USA Department of Electrical and Computer Engineering Northwestern University Evanston Illinois 60208 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA Department of Physics University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA IQUIST University of Illinois at Urbana-Champaign Urbana Illinois 61801 USA Department of Physics Harvard Universi

Just as “classical” information technology rests on a foundation built of interconnected information-processing systems, quantum information technology (QIT) must do the same. A critical component of such systems is the “interconnect,” a device or process that allows transfer of information between disparate physical media, for example, semiconductor electronics, individual atoms, light pulses in optical fiber, or microwave fields. While interconnects have been well engineered for decades in the realm of classical information technology, quantum interconnects (QuICs) present special challenges, as they must allow the transfer of fragile quantum states between different physical parts or degrees of freedom of the system. The diversity of QIT platforms (superconducting, atomic, solid-state color center, optical, etc.) that will form a “quantum internet” poses additional challenges. As quantum systems scale to larger size, the quantum interconnect bottleneck is imminent, and is emerging as a grand challenge for QIT. For these reasons, it is the position of the community represented by participants of the NSF workshop on “Quantum Interconnects” that accelerating QuIC research is crucial for sustained development of a national quantum science and technology program. Given the diversity of QIT platforms, materials used, applications, and infrastructure required, a convergent research program including partnership between academia, industry, and national laboratories is required.

关键词： Cold atoms & matter waves Nonlinear optics Optics & lasers Photonics Quantum communication Quantum computation Quantum error correction Quantum information architectures & platforms Quantum information processing Quantum metrology Quantum optics Atomic systems Optical materials & elements Quantum dots

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Hexagonal Boron Nitride (hBN) as a Low-loss Dielectric for Superconducting Quantum Circuits and Qubits

arXiv

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arXiv 2021年

作者： Wang, Joel I-Jan Yamoah, Megan A. Li, Qing Karamlou, Amir H. Dinh, Thao Kannan, Bharath Braumueller, Jochen Kim, David Melville, Alexander J. Muschinske, Sarah E. Niedzielski, Bethany M. Serniak, Kyle Sung, Youngkyu Winik, Roni Yoder, Jonilyn L. Schwartz, Mollie Watanabe, Kenji Taniguchi, Takashi Orlando, Terry P. Gustavsson, Simon Jarillo-Herrero, Pablo Oliver, William D. Research Laboratory of Electronics Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics 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 Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan

Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. We study the dielectric loss of hexagonal boron nitride (hBN) thin films in the microwave regime by measuring the quality factor of parallel-plate capacitors (PPCs) made of NbSe2-hBN-NbSe2 heterostructures integrated into superconducting circuits. The extracted microwave loss tangent of hBN is bounded to be at most in the mid-10-6 range in the low temperature, single-photon regime. We integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits with coherence times reaching 25 µs, consistent with the hBN loss tangent inferred from resonator measurements. The hBN PPC reduces the qubit feature size by approximately two-orders of magnitude compared to conventional all-aluminum coplanar transmons. Our results establish hBN as a promising dielectric for building high-coherence quantum circuits with substantially reduced footprint and, with a high energy participation that helps to reduce unwanted qubit cross-talk. Copyright © 2021, The Authors. All rights reserved.

关键词： III-V semiconductors

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