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Multipartite entanglement distribution in Bell-pair networks without Steiner trees and with reduced gate cost

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arXiv 2024年

作者： Chelluri, S. Siddardha Khatri, Sumeet van Loock, Peter Institute of Physics Johannes-Gutenberg University of Mainz Staudingerweg 7 Mainz55128 Germany Dahlem Center for Complex Quantum Systems Freie Universität Berlin Berlin14195 Germany Department of Computer Science Virginia Tech BlacksburgVA24061 United States Virginia Tech Center for Quantum Information Science and Engineering BlacksburgVA24061 United States

Multipartite entangled states, particularly Greenberger–Horne–Zeilinger (GHZ) and other graph states, are important resources in multiparty quantum network protocols and measurement-based quantum computing. We consider the problem of generating such states from networks of bipartite entangled (Bell) pairs. Although an optimal protocol (in terms of time steps and consumed Bell pairs) for generating GHZ states in Bell-pair networks has been identified in [Phys. Rev. A 100, 052333 (2019)], it makes use of at most O(N2) gates, where N is the number of nodes in the network. It also involves solving the NP-hard Steiner tree problem as an initial step. Reducing the gate cost is an important consideration now and into the future, because both qubits and gate operations are noisy. To this end, we present a protocol for producing GHZ states in arbitrary Bell-pair networks that provably requires only O(N) gates, and we present numerical evidence that our protocol indeed reduces the gate cost on real-world network models, compared to prior work. Notably, the gate cost of our protocol depends only on the number of nodes and is independent of the topology of the network. At the same time, our protocol maintains nearly the optimal number of consumed Bell pairs, and it avoids finding a Steiner tree or solving any other computationally hard problem by running in polynomial time with respect to N. By considering the number of gates as a figure of merit, our work approaches entanglement distribution from the perspective that, in practice, unlike the traditional information-theoretic setting, local operations and classical communications are not free. Copyright © 2024, The Authors. All rights reserved.

关键词： quantum entanglement

Mechanical Squeezing via Unstable Dynamics in a Microcavity

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Physical Review Letters 2022年第14期128卷 143601-143601页

作者： Katja Kustura Carlos Gonzalez-Ballestero Andrés de los Ríos Sommer Nadine Meyer Romain Quidant Oriol Romero-Isart Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences A-6020 Innsbruck Austria Institute for Theoretical Physics University of Innsbruck A-6020 Innsbruck Austria Nanophotonic Systems Laboratory Department of Mechanical and Process Engineering ETH Zurich 8092 Zurich Switzerland Quantum Center ETH Zurich 8083 Zurich Switzerland

We theoretically show that strong mechanical quantum squeezing in a linear optomechanical system can be rapidly generated through the dynamical instability reached in the far red-detuned and ultrastrong coupling regime. We show that this mechanism, which harnesses unstable multimode quantum dynamics, is particularly suited to levitated optomechanics, and we argue for its feasibility for the case of a levitated nanoparticle coupled to a microcavity via coherent scattering. We predict that for submillimeter-sized cavities the particle motion, initially thermal and well above its ground state, becomes mechanically squeezed by tens of decibels on a microsecond timescale. Our results bring forth optical microcavities in the unresolved sideband regime as powerful mechanical squeezers for levitated nanoparticles, and hence as key tools for quantum-enhanced inertial and force sensing.

关键词： Cavity quantum electrodynamics Optomechanics Squeezing of quantum noise Nanoparticles

Spin-correlation transport and multiple resistive states in multiferroic tunnel junctions

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Physical Review B 2024年第2期110卷 024428-024428页

作者： Xiaolin Zhang Lei Yin Sicong Zhu Ruiqing Cheng Yao Wen Jun He Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology Hubei Province Key Laboratory of Systems Science in Metallurgical Process The State Key Laboratory for Refractories and Metallurgy Collaborative Innovation Center for Advanced Steels International Research Institute for Steel Technology Department of Mechanical Engineering Wuhan Institute of Quantum Technology Wuhan 430206 China

Multiferroic tunneling junctions (MFTJs), which comprise magnetic electrodes and extremely thin ferroelectric tunneling barriers, are promising contenders for nonvolatile memory applications. Noncollinear antiferromagnetic Mn3Sn with time-reversal symmetry-breaking polarization properties and ferroelectric α−In2Se3 may open up the possibility of constructing room-temperature MFTJs. In this study, we investigate the spin-correlation transport in the MFTJs with Mn3Sn/BN/α−In2Se3/Mn3Sn structure using first-principles calculations. The resistance in this structure can be manipulated by tuning the directions of both the Néel vector of Mn3Sn and the electric polarization of the α−In2Se3 layer. Thus, multiple tunneling resistive states can be realized. We predict that huge tunneling magnetoresistance up to 6650% can be obtained by switching the magnetically oriented Néel vectors of Mn3Sn, and more than 8000% tunneling electrical resistance can be obtained by controlling the ferroelectric structure of α−In2Se3. Our work underscores the potential applications of Mn3Sn in multiferroic nonvolatile memories and lays the foundation for the development of ultrafast and efficient spintronic devices utilizing antiferromagnets.

关键词： Fermi surface Ferroelectricity Spintronics First-principles calculations

Variational quantum algorithm for enhanced continuous variable optical phase sensing

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arXiv 2023年

作者： Nielsen, Jens A.H. Kicinski, Mateusz Arge, Tummas N. Vijayadharan, Kannan Foldager, Jonathan Borregaard, Johannes Meyer, Johannes Jakob Neergaard-Nielsen, Jonas S. Gehring, Tobias Andersen, Ulrik L. Center for Macroscopic Quantum States bigQ Department of Physics Technical University of Denmark Fysikvej 307 Kgs. LyngbyDK-2800 Denmark Department of Information Engineering University of Padova Italy Department of Applied Mathematics and Computer Science Technical University of Denmark Denmark Qutech Delft University of Technology Netherlands Department of Physics Harvard University United States Dahlem Center for Complex Quantum Systems Freie Universität Berlin Germany

Variational quantum algorithms (VQAs) are hybrid quantum-classical approaches used for tackling a wide range of problems on noisy intermediate-scale quantum (NISQ) devices. Testing these algorithms on relevant hardware is crucial to investigate the effect of noise and imperfections and to assess their practical value. Here, we implement a variational algorithm designed for optimized parameter estimation on a continuous variable platform based on squeezed light, a key component for high-precision optical phase estimation. We investigate the ability of the algorithm to identify the optimal metrology process, including the optimization of the probe state and measurement strategy for small-angle optical phase sensing. Two different optimization strategies are employed, the first being a gradient descent optimizer using Gaussian parameter shift rules to estimate the gradient of the cost function directly from the measurements. The second strategy involves a gradient-free Bayesian optimizer, fine-tuning the system using the same cost function and trained on the data acquired through the gradient-dependent algorithm. We find that both algorithms can steer the experiment towards the optimal metrology process. However, they find minima not predicted by our theoretical model, demonstrating the strength of variational algorithms in modelling complex noise environments, a non-trivial task. Copyright © 2023, The Authors. All rights reserved.

关键词： Cost functions

quantum Light Generation Based on GaN Microring toward Fully On-Chip Source

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Physical Review Letters 2024年第13期132卷 133603-133603页

作者： Hong Zeng Zhao-Qin He Yun-Ru Fan Yue Luo Chen Lyu Jin-Peng Wu Yun-Bo Li Sheng Liu Dong Wang De-Chao Zhang Juan-Juan Zeng Guang-Wei Deng You Wang Hai-Zhi Song Zhen Wang Li-Xing You Kai Guo Chang-Zheng Sun Yi Luo Guang-Can Guo Qiang Zhou Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China Chengdu 611731 China Key Laboratory of Quantum Physics and Photonic Quantum Information Ministry of Education University of Electronic Science and Technology of China Chengdu 611731 China Department of Electronic Engineering Tsinghua University Beijing 100084 China Department of Fundamental Network Technology China Mobile Research Institute Beijing 100053 China Center for Quantum Internet Tianfu Jiangxi Laboratory Chengdu 641419 China Southwest Institute of Technical Physics Chengdu 610041 China National Key Laboratory of Materials for Integrated Circuits Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 China Institute of Systems Engineering AMS Beijing 100141 China CAS Key Laboratory of Quantum Information University of Science and Technology of China Hefei 230026 China

An integrated quantum light source is increasingly desirable in large-scale quantum information processing. Despite recent remarkable advances, a new material platform is constantly being explored for the fully on-chip integration of quantum light generation, active and passive manipulation, and detection. Here, for the first time, we demonstrate a gallium nitride (GaN) microring based quantum light generation in the telecom C-band, which has potential toward the monolithic integration of quantum light source. In our demonstration, the GaN microring has a free spectral range of 330 GHz and a near-zero anomalous dispersion region of over 100 nm. The generation of energy-time entangled photon pair is demonstrated with a typical raw two-photon interference visibility of 95.5±6.5%, which is further configured to generate a heralded single photon with a typical heralded second-order autocorrelation gH(2)(0) of 0.045±0.001. Our results pave the way for developing a chip-scale quantum photonic circuit.

关键词： quantum entanglement Semiconductor quantum optics

Entanglement-enhanced ac magnetometry in the presence of Markovian noise

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Physical Review A 2025年第4期111卷 042605-042605页

作者： Thanaporn Sichanugrist Hajime Fukuda Takeo Moroi Kazunori Nakayama So Chigusa Norikazu Mizuochi Masashi Hazumi Yuichiro Matsuzaki Department of Physics The University of Tokyo Tokyo 113-0033 Japan International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP) High Energy Accelerator Research Organization (KEK) 1-1 Oho Tsukuba Ibaraki 305-0801 Japan Department of Physics Tohoku University Sendai Miyagi 980-8578 Japan Theoretical Physics Group Lawrence Berkeley National Laboratory Berkeley California 94720 USA Berkeley Center for Theoretical Physics Department of Physics University of California Berkeley California 94720 USA Center for Theoretical Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Institute for Chemical Research Kyoto University Gokasho Uji-city Kyoto 611-0011 Japan Institute of Particle and Nuclear Studies (IPNS) KEK Tsukuba Ibaraki 305-0801 Japan Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science (ISAS) Sagamihara Kanagawa 252-5210 Japan Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU WPI) UTIAS The University of Tokyo Kashiwa Chiba 277-8583 Japan The Graduate University for Advanced Studies (SOKENDAI) Miura District Kanagawa 240-0115 Hayama Japan Department of Electrical Electronic and Communication Engineering Faculty of Science and Engineering Chuo University 1-13-27 Kasuga Bunkyo-ku Tokyo 112-8551 Japan

Entanglement is a resource to improve the sensitivity of quantum sensors. In an ideal case, using an entangled state as a probe to detect target fields, we can beat the standard quantum limit by which all classical sensors are bounded. However, since entanglement is fragile against decoherence, it is unclear whether entanglement-enhanced metrology is useful in a noisy environment. Its benefit is indeed limited when estimating the amplitude of dc magnetic fields under the effect of parallel Markovian decoherence, where the noise operator is parallel to the target field. In this paper, on the contrary, we show an advantage to using an entanglement over the classical strategy under the effect of parallel Markovian decoherence when we try to detect ac magnetic fields. We consider a scenario to induce a Rabi oscillation of the qubits with the target ac magnetic fields. Although we can, in principle, estimate the amplitude of the ac magnetic fields from the Rabi oscillation, the signal becomes weak if the qubit frequency is significantly detuned from the frequency of the ac magnetic field. We show that, by using the Greenberger-Horne-Zeilinger (GHZ) states, we can significantly enhance the signal of the detuned Rabi oscillation even under the effect of parallel Markovian decoherence. Our method is based on the fact that the interaction time between the GHZ states and ac magnetic fields scales as 1/L to mitigate the decoherence effect, where L is the number of qubits, which contributes to improving the bandwidth of the detectable frequencies of the ac magnetic fields. Our results pave the way for new applications of entanglement-enhanced ac magnetometry.

关键词： Qubits

Two-Stage Inverse Design of Superchiral Dielectric Metasurfaces

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Two-Stage Inverse Design of Superchiral Dielectric Metasurfa...

International Review of Progress in Applied Computational Electromagnetics (ACES)

作者： Omer Yesilyurt Vahagn Mkhitaryan Jer-Shing Huang Ilya Shadrivov Alexander V. Kildishev Elmore Family School of Electrical and Computer Engineering Birck Nanotechnology Center and Purdue Quantum Science and Engineering Institute Purdue University West Lafayette IN USA Department of Energy (DOE) The Quantum Science Center (QSC) a National Quantum Information Science Research Center of the U.S. Oak Ridge TN USA Leibniz Institute of Photonic Technology Jena Germany ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS) Research School of Physics the Australian National University Canberra Australia

ISBN: (数字)9781733509671

ISBN: (纸本)9798350362978

Chirality is a fundamental property of asymmetry and is crucial in distinguishing molecular enantiomers, with profound implications across chemistry, biology, and materials science. Circular dichroism (CD) spectroscopy, which measures the differential absorption of left-handed (LCP) and right-handed (RCP) circularly polarized light, serves as a conventional method for identifying and separating chiral enantiomers. Nevertheless, due to the inherently weak chiral-optical interactions, the CD signals of numerous chiral molecules are minimal, typically spanning 10– 3 to 10– 6 within the ultraviolet spectrum. Superchiral metasurfaces, producing fields with enhanced optical chirality that surpasses the chirality of circularly polarized light, emerge as a solution to this challenge. Such metasurfaces, with enhanced interaction between light and chiral molecules, offer a significant increase in CD signal, underscoring the necessity for their advanced development for more accurate and sensitive analysis. This study presents a novel, two-stage inverse design methodology for superchiral metasurfaces with iterative optimization of the topology of a dielectric metasurface unit cell to enhance optical chiral density in the near field. In the first stage, a neural network-based optimizer works in tandem with a rigorous coupled wave analysis (RCWA) solver. In the second stage, adjoint gradients of the optical chirality density are derived from the first principles and calculated with a Finite Difference Time Domain (FDTD) scheme. Our results offer a new platform for high-sensitivity CD spectroscopy applications, allowing for fast, constrained optimization of the unit cells.

关键词： Spectroscopy Optical polarization Biomedical optical imaging Metasurfaces Optical network units Optical coupling Optical sensors

Disentangling real space fluctuations: the diagnostics of metal-insulator transitions beyond single-particle spectral functions

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arXiv 2025年

作者： Meixner, Michael Krämer, Marcel Wentzell, Nils Bonetti, Pietro M. Andergassen, Sabine Toschi, Alessandro Schäfer, Thomas Max-Planck-Institut für Festkörperforschung Heisenbergstraße 1 Stuttgart70569 Germany Institute of Information Systems Engineering TU Wien Vienna1040 Austria Center for Computational Quantum Physics Flatiron Institute 162 5th Avenue New YorkNY10010 United States Department of Physics Harvard University CambridgeMA02138 United States Institute of Solid State Physics TU Wien Vienna1040 Austria

The destruction of metallicity due to the mutual Coulomb interaction of quasiparticles gives rise to fascinating phenomena of solid state physics such as the Mott metal-insulator transition and the pseudogap. A key observable characterizing their occurrences is the single-particle spectral function, determined by the fermionic self-energy. In this paper we investigate in detail how real space fluctuations are responsible for a self-energy that drives the Mott-Hubbard metal-insulator transition. To this aim we first introduce a real space fluctuation diagnostics approach to the Hedin equation, which connects the fermion-boson coupling vertex λ to the self-energy Σ. Second, by using cellular dynamical mean-field theory calculations for λ we identify the leading physical processes responsible for the destruction of metallicity across the transition. Copyright © 2025, The Authors. All rights reserved.

关键词： Metal insulator transition

Supercurrent-carrying supersolid in spin-orbit-coupled Bose-Einstein condensates

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arXiv 2023年

作者： Lyu, Hao Chen, Yuanyuan Zhu, Qizhong Zhang, Yongping Institute for Quantum Science and Technology Department of Physics Shanghai University Shanghai200444 China Quantum Systems Unit Okinawa Institute of Science and Technology Graduate University Okinawa Onna904-0495 Japan Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials School of Physics South China Normal University Guangzhou510006 China Guangdong-Hong Kong Joint Laboratory of Quantum Matter Frontier Research Institute for Physics South China Normal University Guangzhou510006 China

One of brilliant achievements in spin-orbit-coupled Bose-Einstein condensates is the discovery and observation of the supersolid stripe states. So far, all studied supersolid stripe states do not carry supercurrent. In this paper, we reveal the existence of supercurrent-carrying supersolids in spin-orbit-coupled Bose-Einstein condensates. The supersolid family has a parabolic-like dispersion and carries supercurrent which is proportional to the quasimomentum. Energetic and dynamical instabilities can break supercurrent-carrying ability of this supersolid family. An insightful interpretation of the dynamical instability of supercurrent-carrying supersolids from the pure plane-wave phase is provided. © 2023, CC BY.

关键词： Statistical mechanics