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Experimental evidence for the two-path description of neutron spin echo

Physical Review A 2024年第4期109卷 042420-042420页

作者： S. McKay A. A. M. Irfan Q. Le Thien N. Geerits S. R. Parnell R. M. Dalgliesh N. V. Lavrik I. I. Kravchenko G. Ortiz R. Pynn Department of Physics Indiana University Bloomington Indiana 47405 USA Center for Exploration of Energy and Matter Indiana University Bloomington Indiana 47408 USA Atominstitut TU Wien Stadionallee 2 1020 Vienna Austria Faculty of Applied Sciences Delft University of Technology Mekelweg 15 2629 JB Delft The Netherlands ISIS Rutherford Appleton Laboratory Chilton Oxfordshire OX11 0QX United Kingdom Center for Nanophase Materials Science Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Science and Engineering Center Indiana University Bloomington Indiana 47408 USA Institute for Quantum Computing University of Waterloo Waterloo Ontario Canada N2L 3G1 Neutron Sciences Directorate Oak Ridge National Laboratory Oak Ridge Tennessee 37830 USA

We describe an experiment that strongly supports a two-path interferometric model in which the spin-up and spin-down components of each neutron propagate coherently along spatially separated parallel paths in a typical neutron spin-echo small-angle scattering (SESANS) experiment. Specifically, we show that the usual semi-classical, single-path treatment of Larmor precession of a polarized neutron in an external magnetic field predicts a damping as a function of the spin-echo length of the SESANS signal obtained with a periodic phase grating when the transverse width of the neutron wave packet is finite. However, no such damping is observed experimentally, implying either that the Larmor model is incorrect or that the transverse extent of the wave packet is very large. In contrast, we demonstrate theoretically that a quantum-mechanical interferometric model in which the two mode-entangled (i.e., intraparticle entangled) spin states of a single neutron are separated in space when they interact with the grating accurately predicts the measured SESANS signal, which is independent of the wave packet width.

关键词： quantum entanglement Interferometry Neutron spin echo spectroscopy Spin echo small angle neutron scattering

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Maximum entropy methods for quantum state compatibility problems

arXiv

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arXiv 2022年

作者： Hou, Shi-Yao Wu, Zipeng Zeng, Jinfeng Cao, Ningping Cao, Chenfeng Li, Youning Zeng, Bei College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu610068 China Shenzhen SpinQ Technology Co. Ltd. Shenzhen China Department of Physics The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong Beijing Academy of Quantum Information Sciences Beijing100193 China Institute for Quantum Computing University of Waterloo WaterlooON Canada College of Science China Agricultural University Beijing100080 China

Inferring a quantum system from incomplete information is a common problem in many aspects of quantum information science and applications, where the principle of maximum entropy (MaxEnt) plays an important role. The quantum state compatibility problem asks whether there exists a density matrix ρ compatible with some given measurement results. Such a compatibility problem can be naturally formulated as a semidefinite programming (SDP), which searches directly for the existence of a ρ. However, for large system dimensions, it is hard to represent ρ directly, since it needs too many parameters. In this work, we apply MaxEnt to solve various quantum state compatibility problems, including the quantum marginal problem. An immediate advantage of the MaxEnt method is that it only needs to represent ρ via a relatively small number of parameters, which is exactly the number of the operators measured. Furthermore, in case of incompatible measurement results, our method will further return a witness that is a supporting hyperplane of the compatible set. Our method has a clear geometric meaning and can be computed effectively with hybrid quantum-classical algorithms. © 2022, CC BY-SA.

关键词： Maximum entropy methods

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Performance limits due to thermal transport in graphene single-photon bolometers

arXiv

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arXiv 2023年

作者： Fried, Caleb Jordan Russell, B. Arnault, Ethan G. Huang, Bevin Lee, Gil-Ho Englund, Dirk Henriksen, Erik A. Fong, Kin Chung Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology CambridgeMA02139 United States Department of Earth and Planetary Sciences Harvard University CambridgeMA02138 United States Department of Physics Harvard University CambridgeMA02138 United States Raytheon BBN Quantum Engineering and Computing Group CambridgeMA02138 United States Department of Physics Washington University in St. Louis St. LouisMO United States Intelligence Community Postdoctoral Research Fellowship Program Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics Pohang University of Science and Technology Pohang790-784 Korea Republic of

In high-sensitivity bolometers and calorimeters, the photon absorption often occurs at a finite distance from the temperature sensor to accommodate antennas or avoid the degradation of superconducting circuitry exposed to radiation. As a result, thermal propagation from the input to the temperature readout can critically affect detector performance. In this report we model the performance of a graphene bolometer, accounting for electronic thermal diffusion and dissipation via electron-phonon coupling at low temperatures in three regimes: clean, supercollision, and resonant scattering. Our results affirm the feasibility of a superconducting readout without Cooper-pair breaking by mid- and near-infrared photons, and provide a recipe for designing graphene absorbers for calorimetric single-photon detectors. We investigate the tradeoff between the input-readout distance and detector efficiency, and predict an intrinsic timing jitter of ∼2.7 ps. Based on our result, we propose a spatial-mode-resolving photon detector to increase communication bandwidth. Copyright © 2023, The Authors. All rights reserved.

关键词： Graphene

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Variational learning algorithms for quantum query complexity

arXiv

引用

arXiv 2022年

作者： Wu, Zipeng Hou, Shi-Yao Zhang, Chao Li, Lvzhou Zeng, Bei Department of Physics The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu610068 China Shenzhen SpinQ Technology Co. Ltd. Shenzhen China Institute of Quantum Computing and Computer Theory School of Computer Science and Engineering Sun Yat-sen University Guangzhou510006 China

quantum query complexity is pivotal in the analysis of quantum algorithms, encompassing wellknown examples like search and period-finding algorithms. These algorithms typically involve a sequence of unitary operations and oracle calls dependent on an input variable. In this study, we introduce a variational learning approach to explore quantum query complexity. Our method employs an efficient parameterization of the unitary operations and utilizes a loss function derived from the algorithm's error probability. We apply this technique to various quantum query complexities, notably devising a new algorithm that resolves the 5-bit Hamming modulo problem with four queries, addressing an open question from arXiv:2112.14682. This finding is corroborated by a Semidefinite Programming (SDP) approach. Our numerical method exhibits superior memory efficiency compared to SDP and can identify quantum query algorithms that require a smaller workspace register dimension, an aspect not optimized by SDP. These advancements present a significant step forward in the practical application and understanding of quantum query algorithms. Copyright © 2022, The Authors. All rights reserved.

关键词： Learning algorithms

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An improved differential evolution algorithm for learning high-fidelity quantum controls

引用

Science Bulletin 2019年第19期64卷 1402-1408页

作者： Xiaodong Yang Jun Li Xinhua Peng CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics University of Science and Technology of ChinaHefei230026China Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and TechnologyShenzhen518055China Center for Quantum Computing Peng Cheng LaboratoryShenzhen518055China Shenzhen Key Laboratory of Quantum Science and Engineering Southern University of Science and TechnologyShenzhen518055China Synergetic Innovation Centre of Quantum Information&Quantum Physics University of Science and Technology of ChinaHefei230026China

Precisely and efficiently designing control pulses for the preparation of quantum states and quantum gates are the fundamental tasks for quantum ***-based optimal control methods are the routine to design such ***,the gradient information is often difficult to calculate or measure,especially when the system is not well calibrated or in the presence of various ***-free evolutionary algorithm is an alternative choice to accomplish this task but usually with ***,we design an efficient mutation rule by using the information of the current and the former individuals *** leads to our improved differential evolution algorithm,called da *** demonstrate its performance,we numerically benchmark the pulse optimization for quantum states and quantum gates preparations on small-scale NMR *** numerical comparisons with conventional differential evolution algorithms show that da DE has great advantages on the convergence speed and robustness to several uncertainties including pulse imperfections and measurement errors.

关键词： Control pulses searching Differential evolution quantum states and gates preparation Pulse imperfections Random measurement errors

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On a gap in the proof of the generalised quantum Stein's lemma and its consequences for the reversibility of quantum resources

arXiv

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arXiv 2022年

作者： Berta, Mario Brandão, Fernando G.S.L. Gour, Gilad Lami, Ludovico Plenio, Martin B. Regula, Bartosz Tomamichel, Marco Institute for Quantum Information RWTH Aachen University Aachen Germany Department of Computing Imperial College London London United Kingdom Institute for Quantum Information and Matter California Institute of Technology PasadenaCA United States AWS Center for Quantum Computing PasadenaCA United States Department of Mathematics and Statistics Institute for Quantum Science and Technology University of Calgary ABT2N 1N4 Canada Institut für Theoretische Physik und IQST Universität Ulm Albert-Einstein-Allee 11 UlmD-89069 Germany QuSoft Science Park 123 Amsterdam1098 XG Netherlands Korteweg–de Vries Institute for Mathematics University of Amsterdam Science Park 105-107 Amsterdam1098 XG Netherlands Institute for Theoretical Physics University of Amsterdam Science Park 904 Amsterdam1098 XH Netherlands Saitama Wako351-0198 Japan Department of Physics Graduate School of Science The University of Tokyo Bunkyo-ku Tokyo113-0033 Japan Center for Quantum Technologies National University of Singapore Singapore Department of Electrical and Computer Engineering College of Design and Engineering National University of Singapore Singapore

We show that the proof of the generalised quantum Stein’s lemma [Brandão & Plenio, Commun. Math. Phys. 295, 791 (2010)] is not correct due to a gap in the argument leading to Lemma III.9. Hence, the main achievability result of Brandão & Plenio is not known to hold. This puts into question a number of established results in the literature, in particular the reversibility of quantum entanglement [Brandão & Plenio, Commun. Math. Phys. 295, 829 (2010);Nat. Phys. 4, 873 (2008)] and of general quantum resources [Brandão & Gour, Phys. Rev. Lett. 115, 070503 (2015)] under asymptotically resource non-generating operations. We discuss potential ways to recover variants of the newly unsettled results using other approaches. © 2022, CC BY.

关键词： quantum entanglement

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Error Suppression for Arbitrary-Size Black Box quantum Operations

arXiv

引用

arXiv 2022年

作者： Lee, Gideon Hann, Connor T. Puri, Shruti Girvin, S.M. Jiang, Liang Pritzker School of Molecular Engineering The University of Chicago ChicagoIL60637 United States Department of Applied Physics Yale University New HavenCT06520 United States Department of Physics Yale University New HavenCT06511 United States Yale Quantum Institute New HavenCT06520 United States AWS Center for Quantum Computing PasadenaCA91125 United States IQIM California Institute of Technology PasadenaCA91125 United States

Efficient suppression of errors without full error correction is crucial for applications with NISQ devices. Error mitigation allows us to suppress errors in extracting expectation values without the need for any error correction code, but its applications are limited to estimating expectation values, and cannot provide us with high-fidelity quantum operations acting on arbitrary quantum states. To address this challenge, we propose to use error filtration (EF) for gate-based quantum computation, as a practical error suppression scheme without resorting to full quantum error correction. The result is a general-purpose error suppression protocol where the resources required to suppress errors scale independently of the size of the quantum operation, and does not require any logical encoding of the operation. The protocol provides error suppression whenever an error hierarchy is respected – that is, when the ancilliary cSWAP operations are less noisy than the operation to be corrected. We further analyze the application of EF to quantum random access memory, where EF offers hardware-efficient error suppression. © 2022, CC BY.

关键词： Error correction

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Exploring the Relationship between Deposition Method, Microstructure, and Performance of Nb/Si-Based Superconducting Coplanar Waveguide Resonators

SSRN

引用

SSRN 2024年

作者： Oh, Jin-Su Kopas, Cameron J. Marshall, Jayss Fang, Xiaotian Joshi, Kamal R. Datta, Amlan Ghimire, Sunil Park, Joong-Mok Kim, Richard Setiawan, Daniel Lachman, Ella Mutus, Joshua Y. Murthy, Akshay A. Grassellino, Anna Romanenko, Alex Zasadzinski, John Wang, Jigang Prozorov, Ruslan Yadavalli, Kameshwar Kramer, Matt Zhou, Lin Ames National Laboratory AmesIA50011 United States Rigetti Computing BerkeleyCA94710 United States Department of Physics & Astronomy Iowa State University AmesIA50011 United States Superconducting Quantum Materials and Systems Division Fermi National Accelerator Laboratory BataviaIL60510 United States Department of Physics Illinois Institute of Technology ChicagoIL60616 United States Department of Materials Science and Engineering Iowa State University AmesIA50011 United States

Superconducting quantum circuits (SQC) are one of the most promising hardware platforms for quantum computing, yet their performance is currently limited by the presence of various structural defects inside the circuit’s structure. Despite impressive progress in the past decade, a precise understanding of the origin of these defects from various fabrication processes and their impact on coherence is still lacking. In this study, we performed a comprehensive investigation on the microstructure, superconductivity, and resonator quality factor of Nb films deposited by high-power impulse magnetron sputtering (HiPIMS) and direct current (DC) magnetron sputtering. A suite of characterization techniques, including electron microscopy with spectroscopy, secondary ion mass spectrometry, magneto-optical microscopy, and pump-probe reflectivity spectroscopy is used. We reveal that niobium (Nb) resonators fabricated using HiPIMS exhibit a smaller average grain size, thicker surface oxide with larger thickness variations (rougher surface), and a thicker amorphous Nb/Si interface layer compared to samples deposited by DC sputtering. We identified that the amorphous Nb oxides (mainly located at the Nb surface and along the grain boundaries) and Nb-Si amorphous layers (at the Nb/Si interface) are major and potential sources of two-level system (TLS), while off-stochiometric oxides and suboxides of Nb close to the surface, crystalline defects (i.e., dislocations at GB, point defects introduced during deposition) are main contributors of non-TLS sources. Our findings clarify the relationship between different defects and coherence loss mechanisms, highlighting the importance of material microstructure control on performance optimization in SQC. © 2024, The Authors. All rights reserved.

关键词： Grain boundaries

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Ultralow Off-State Current and Multilevel Resistance State in Van der Waals Heterostructure Memristors

引用

Advanced Functional Materials 2024年第15期34卷

作者： Liu, Xinling Zhang, Chi Li, Enlong Gao, Caifang Wang, Ruixue Liu, Yu Liu, Fucai Shi, Wu Yuan, Yahua Sun, Jian Lin, Yen-Fu Chu, Junhao Li, Wenwu State Key Laboratory of Photovoltaic Science and Technology Department of Materials Science Fudan University Shanghai200433 China Shanghai Frontiers Science Research Base of Intelligent Optoelectronics and Perception Institute of Optoelectronics Fudan University Shanghai200433 China East China Normal University Shanghai200241 China School of Optoelectronic Science and Engineering University of Electronic Science and Technology of China Chengdu610054 China University of Electronic Science and Technology of China Huzhou313098 China State Key Laboratory of Surface Physics Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai200433 China School of Physics Central South University Changsha410083 China National Chung Hsing University Taichung40227 Taiwan

Memristors based on 2D semiconductors hold great promise due to their atomic-level thickness and tunable optoelectronic properties. However, a significant challenge lies in suppressing the large off-state current, which leads to additional standby power consumption. Here, a simple and versatile method is presented to address this issue by introducing a thin h-BN interlayer between 2D semiconductors and the electrodes. The thickness of the h-BN interlayer serves as a pivotal parameter for modulating the interfacial Schottky barrier, thereby influencing the off-state current level. This fabricated graphene/α-In2Se3/h-BN/Cr-Au memristor, forming a van der Waals heterostructure, exhibits unipolar resistive switching behavior. Remarkably, the memristor incorporating an 8 nm h-BN interlayer showcases an ultralow off-state current of 4.2 × 10−13 A, five orders of magnitude lower than that without the h-BN interlayer. It also achieves a current switching on/off ratio of up to 109 and realizes 32 distinct resistance states, enabling robust multi-bit memory capabilities. Excellent stability and durability are maintained due to the self-encapsulation of the h-BN interlayer. Furthermore, this method is also applicable to memristors built on HfS2, WS2, and WSe2, highlighting its broad potential for technological applications. © 2023 Wiley-VCH GmbH.

关键词： Heterojunctions

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Generic detection-based error mitigation using quantum autoencoders

引用

Physical Review A 2021年第4期103卷 L040403-L040403页

作者： Xiao-Ming Zhang Weicheng Kong Muhammad Usman Farooq Man-Hong Yung Guoping Guo Xin Wang Department of Physics City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong SAR China Origin Quantum Computing Company Limited Hefei Anhui 230088 China Department of Mathematics City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong SAR China Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518055 China Shenzhen Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China CAS Key Laboratory of Quantum Information University of Science and Technology of China Hefei Anhui 230026 China City University of Hong Kong Shenzhen Research Institute Shenzhen Guangdong 518057 China

Efficient error-mitigation techniques demanding minimal resources is key to quantum information processing. We propose a generic protocol to mitigate quantum errors using detection-based quantum autoencoders. In our protocol, the quantum data are compressed into a latent subspace while leaving errors outside, the latter of which is then removed by a measurement and postselection. Compared to previously developed methods, our protocol on the one hand requires no extra qubits, and on the other hand it has a near-optimal denoising power, in which under reasonable requirements all errors detected outside of the latent subspace can be removed, while those inside the subspace cannot be removed by any means. Our detection-based quantum autoencoders are therefore particularly useful for near-term quantum devices in which controllable qubits are limited while noise reduction is important.

关键词： Machine learning quantum control quantum information processing

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