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High-Threshold quantum computing by Fusing One-Dimensional Cluster States

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Physical Review Letters 2023年第12期131卷 120603-120603页

作者： Stefano Paesani Benjamin J. Brown Center for Hybrid Quantum Networks (Hy-Q) Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen 2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen 2100 Denmark IBM Quantum T. J. Watson Research Center Yorktown Heights New York 10598 USA IBM Denmark Prøvensvej 1 Brøndby 2605 Denmark

We propose a measurement-based model for fault-tolerant quantum computation that can be realized with one-dimensional cluster states and fusion measurements only; basic resources that are readily available with scalable photonic hardware. Our simulations demonstrate high thresholds compared with other measurement-based models realized with basic entangled resources and 2-qubit fusion measurements. Its high tolerance to noise indicates that our practical construction offers a promising route to scalable quantum computing with quantum emitters and linear-optical elements.

关键词： Measurement-based quantum computing Optical quantum information processing quantum computation quantum error correction quantum information architectures & platforms

Programmable Photonic Nonlinearity for quantum Simulation

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Programmable Photonic Nonlinearity for Quantum Simulation

Asia Communications and Photonics Conference and Exhibition (ACP)

作者： Ying Wang Kasper H. Nielsen Edward Deacon Patrik I. Sund Zhe Liu Sven Scholz Arne Ludwig Leonardo Midolo Anders S. Sørensen Stefano Paesani Peter Lodahl Center for Hybrid Quantum Networks (Hy-Q) Niels Bohr Institute University of Copenhagen Copenhagen Denmark Quantum Engineering and Technology Laboratories School of Physics Bristol UK Department of Electrical and Electronic Engineering University of Bristol Bristol UK Lehrstuhl für Angewandte Festkörperphysik Ruhr-Universität Bochum Bochum Germany Center for Hybrid Quantum Networks (Hy-Q) NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen Denmark

ISBN: (数字)9798350379266

ISBN: (纸本)9798350379273

Light-matter interaction at the quantum level provides a versatile interface driving photonic quantum technologies toward practical applications. We demonstrate multi-mode photonic circuits that enable precise programming of linear and nonlinear phase configurations at the single-photon level. The nonlinearity operation is realized using a solid-state quantum emitter, a self-assembled quantum dot, integrated into a nanophotonic device. The quantum dot interfaces with a temporal linear optical interferometer, creating a programmable nonlinear photonic platform that is necessary for implementing quantum protocols that require strong nonlinearities, such as the quantum simulation of anharmonic molecular dynamics.

关键词： Optical interferometry Self-assembly Protocols Stimulated emission quantum dots Programming Nonlinear optical devices Optical fiber communication Photonics quantum simulation

Computational discovery of high-refractive-index van der Waals materials: The case of HfS2

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arXiv 2025年

作者： Zambrana-Puyalto, Xavier Svendsen, Mark Kamper Søndersted, Amalie H. Sarbajna, Avishek Sandberg, Joakim P. Riber, Albert L. Ermolaev, Georgy Boland, Tara Maria Tselikov, Gleb Volkov, Valentyn S. Thygesen, Kristian S. Raza, Søren Department of Physics Technical University of Denmark Fysikvej Kongens Lyngby DK-2800 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Emerging Technologies Research Center XPANCEO Internet City Emmay Tower Dubai United Arab Emirates

New high-refractive-index dielectric materials may enhance many optical technologies by enabling efficient manipulation of light in waveguides, metasurfaces, and nanoscale resonators. Van der Waals materials are particularly promising due to their excitonic response and strong in-plane polarizability. Here we combine ab initio calculations and experiments to discover new high-refractive-index materials. Our screening highlights both known and new promising optical materials, including hafnium disulfide (HfS2), which shows an in-plane refractive index above 3 and large anisotropy in the visible range. We confirm these theoretical predictions through ellipsometry measurements and investigate the photonic potential of HfS2 by fabricating nanodisk resonators, observing optical Mie resonances in the visible spectrum. Over the course of seven days, we observe a structural change in HfS2, which we show can be mitigated by storage in either argon-rich or humidity-reduced environments. This work provides a comparative overview of high-index van der Waals materials and showcases the potential of HfS2 for photonic applications in the visible spectrum. © 2025, CC BY-SA.

关键词： Van der Waals forces

Fault-tolerant quantum simulation of generalized Hubbard models

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arXiv 2025年

作者： Bay-Smidt, Andreas Juul Klausen, Frederik Ravn Sünderhauf, Christoph Izsák, Róbert Solomon, Gemma C. Blunt, Nick S. NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Nano-Science Center Department of Chemistry University of Copenhagen Denmark Princeton University Department of Mathematics Fine Hall United States Riverlane CambridgeCB2 3BZ United Kingdom

quantum simulations of strongly interacting fermionic systems, such as those described by the Hubbard model, are promising candidates for useful early fault-tolerant quantum computing applications. This paper presents Tile Trotterization, a generalization of plaquette Trotterization (PLAQ), which allows simulation of Hubbard models on arbitrary lattices and provides a framework that enables the simulation of more complex models, including the extended Hubbard model and the PPP model. We consider applications of Tile Trotterization to simulate Hubbard models on hexagonal lattice fragments and periodic hexagonal lattices, analyze gate costs, and provide commutator bounds for evaluating Trotter errors, including new commutator bounds for the extended Hubbard model. We compare the resource requirements of Tile Trotterization for performing quantum phase estimation to a qubitization-based approach, which we optimize for the hexagonal lattice Hubbard model, and demonstrate that Tile Trotterization scales more efficiently with system size. These advancements significantly broaden the potential applications of early fault-tolerant quantum computers to models of practical interest in materials research and organic chemistry. Copyright © 2025, The Authors. All rights reserved.

关键词： Hubbard model

Ground-state phase diagram and parity-flipping microwave transitions in a gate-tunable Josephson junction

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Physical Review B 2024年第13期109卷 134506-134506页

作者： M. R. Sahu F. J. Matute-Cañadas M. Benito P. Krogstrup J. Nygård M. F. Goffman C. Urbina A. Levy Yeyati H. Pothier Quantronics group Service de Physique de l'État Condensé (CNRS UMR 3680) IRAMIS CEA-Saclay Université Paris-Saclay 91191 Gif-sur-Yvette France Departamento de Física Teórica de la Materia Condensada Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera Universidad Autónoma de Madrid 28049 Madrid Spain NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Universitetsparken 5 2100 Copenhagen Denmark Center for Quantum Devices Niels Bohr Institute University of Copenhagen Universitetsparken 5 2100 Copenhagen Denmark

We probed a gate-tunable InAs nanowire Josephson weak link by coupling it to a microwave resonator. Tracking the resonator frequency shift when the weak link is close to pinch-off, we observe that the ground state of the latter alternates between a singlet and a doublet when varying either the gate voltage or the superconducting phase difference across it. The corresponding microwave absorption spectra display lines that approach zero energy close to the singlet-doublet boundaries, suggesting parity-flipping transitions, which are in principle forbidden in microwave spectroscopy and expected to arise only in tunnel spectroscopy. We tentatively interpret them by means of an ancillary state isolated in the junction acting as a reservoir for individual electrons.

关键词： Andreev reflection Circuit quantum electrodynamics Mesoscopics Nanowires quantum dots Anderson impurity model

Gate-tunable Superconductivity in Hybrid InSb-Pb Nanowires

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arXiv 2023年

作者： Chen, Yan van Driel, David Lampadaris, Charalampos Khan, Sabbir A. Alattallah, Khalifah Zeng, Lunjie Olsson, Eva Dvir, Tom Krogstrup, Peter Liu, Yu Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark QuTech and Kavli Institute of NanoScience Delft University of Technology Delft2600 GA Netherlands Department of Physics Chalmers University of Technology Gothenburg41296 Sweden NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Danish Fundamental Metrology Hørsholm2970 Denmark

We present a report on hybrid InSb-Pb nanowires that combine high spin-orbit coupling with a high critical field and a large superconducting gap. Material characterization indicates the Pb layer of high crystal quality on the nanowire side facets. Hard induced superconducting gaps and gate-tunable supercurrent are observed in the hybrid nanowires. These results showcase the promising potential of this material combination for a diverse range of applications in hybrid quantum transport devices. © 2023, CC BY.

关键词： III-V semiconductors

Collective formation of misfit dislocations at the critical thickness for equilibrium nanowire heterostructures

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arXiv 2021年

作者： Thann, Thue Christian Særkjær, Tobias Schuwalow, Sergej Krogstrup, Peter NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark

In this work we model the evolution of strain energy during different growth stages of heterostructure nanowires. We find that the minimum energy configuration changes abruptly from fully elastically strained to partially relaxed due to collective formation of a misfit dislocation network. The transition at the critical thickness is associated with a characteristic density of misfits. These insights are gained from a technique developed to simulate misfit dislocations in a finite element framework, incorporating both elastic and plastic relaxation in a stationary heterostructure. We argue that these results have general relevance for mismatched heterostructures. © 2021, CC BY.

关键词： Heterojunctions

Subgap-state-mediated transport in superconductor–semiconductor hybrid islands: Weak and strong coupling regimes

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arXiv 2024年

作者： Valentini, Marco Souto, Rubén Seoane Borovkov, Maksim Krogstrup, Peter Meir, Yigal Leijnse, Martin Danon, Jeroen Katsaros, Georgios Institute of Science and Technology Austria Am Campus 1 Klosterneuburg3400 Austria Madrid Spain Lund University Box 118 Lund22100 Sweden Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Universitetsparken 5 Copenhagen2100 Denmark Department of Physics Ben-Gurion University of the Negev Beer-Sheva84105 Israel Department of Physics Norwegian University of Science and Technology TrondheimNO-7491 Norway

Superconductor–semiconductor hybrid systems play a crucial role in realizing nanoscale quantum devices, including hybrid qubits, Majorana bound states, and Kitaev chains. For such hybrid devices, subgap states play a prominent role in their operation. In this work, we study such subgap states via Coulomb and tunneling spectroscopy through a superconducting island defined in a semiconductor nanowire fully coated by a superconductor. We systematically explore regimes ranging from an almost decoupled island to the open configuration. In the weak coupling regime, the experimental observations are very similar in the absence of a magnetic field and when one flux quantum is piercing the superconducting shell. Conversely, in the strong coupling regime, significant distinctions emerge between the two cases. We ascribe this different behavior to the existence of subgap states at one flux quantum, which become observable only for sufficiently strong coupling to the leads. We support our interpretation using a simple model to describe transport through the island. Our study highlights the importance of studying a broad range of tunnel couplings for understanding the rich physics of hybrid devices. © 2024, CC BY.

关键词： Superconducting materials

Modular Autonomous Virtualization System for Two-Dimensional Semiconductor quantum Dot Arrays

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Physical Review X 2025年第2期15卷 021034-021034页

作者： Anantha S. Rao Donovan Buterakos Barnaby van Straaten Valentin John Cécile X. Yu Stefan D. Oosterhout Lucas Stehouwer Giordano Scappucci Menno Veldhorst Francesco Borsoi Justyna P. Zwolak Joint Center for Quantum Information and Computer Science University of Maryland College Park Maryland 20742 USA Department of Physics University of Maryland College Park Maryland 20742 USA National Institute of Standards and Technology Gaithersburg Maryland 20899 USA QuTech and Kavli Institute of Nanoscience Delft University of Technology P.O. Box 5046 2600 GA Delft The Netherlands QuTech and Netherlands Organisation for Applied Scientific Research (TNO) Delft The Netherlands Present address: NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 2100 Copenhagen Denmark.

Arrays of gate-defined semiconductor quantum dots are among the leading candidates for building scalable quantum processors. High-fidelity initialization, control, and readout of spin qubit registers require exquisite and targeted control over key Hamiltonian parameters that define the electrostatic environment. However, due to the tight gate pitch, capacitive crosstalk between gates hinders independent tuning of chemical potentials and interdot couplings. While virtual gates offer a practical solution, determining all the required cross-capacitance matrices accurately and efficiently in large quantum dot registers is an open challenge. Here, we establish a modular automated virtualization system (MAViS)—a general and modular framework for autonomously constructing a complete stack of multilayer virtual gates in real time. Our method employs machine learning techniques to rapidly extract features from two-dimensional charge stability diagrams. We then utilize computer vision and regression models to self-consistently determine all relative capacitive couplings necessary for virtualizing plunger and barrier gates in both low- and high-tunnel-coupling regimes. Using MAViS, we successfully demonstrate accurate virtualization of a dense two-dimensional array comprising ten quantum dots defined in a high-quality Ge/SiGe heterostructure. Our work offers an elegant and practical solution for the efficient control of large-scale semiconductor quantum dot systems.

关键词： Semiconductor quantum dots