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Andreev spin relaxation time in a shadow-evaporated InAs weak link

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arXiv 2025年

作者： Lu, Haoran Bofill, David F. Sun, Zhenhai Kanne, Thomas Nygård, Jesper Kjaergaard, Morten Fatemi, Valla School of Applied and Engineering Physics Cornell University IthacaNY14853 United States Center for Quantum Devices Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark

Andreev spin qubits are a new qubit platform that merges superconductivity with semiconductor physics. The mechanisms dominating observed energy relaxation remain unidentified. We report here on three steps taken to address these questions in an InAs nanowire weak link. First, we designed a microwave readout circuit tuned to be directly sensitive to the spin-dependent inductance of the weak link so that higher orbital states are not necessary for readout – this resulted in larger windows in parameter space in which the spin state properties can be probed. Second, we implemented a successful gap-engineering strategy to mitigate quasiparticle poisoning. Third, the weak link was fabricated by in situ shadow evaporation, which has been shown to improve atomic-scale disorder. We show how our design allows characterization of the spin stability and coherence over the full range of magnetic flux and gate voltage of an odd parity bias point. The spin relaxation and dephasing rates are comparable with the best devices previously reported, suggestive that surface atomic-scale disorder and QP poisoning are not linked to spin relaxation in InAs nanowires. Our design strategies are transferrable to novel materials platforms for Andreev qubits such as germanium and carbon. © 2025, CC BY.

关键词： Nanowires

quantum Geometry and Bounds on Dissipation in Slowly Driven quantum Systems

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Physical Review Letters 2025年第14期134卷 146603-146603页

作者： Iliya Esin Étienne Lantagne-Hurtubise Frederik Nathan Gil Refael Department of Physics and Institute for Quantum Information and Matter California Institute of Technology Pasadena California 91125 USA Department of Physics Bar-Ilan University 52900 Ramat Gan Israel Département de Physique and Institut Quantique Université de Sherbrooke Sherbrooke Québec J1K 2R1 Canada Center for Quantum Devices and NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen 2100 Copenhagen Denmark

We show that energy dissipation in slowly driven, Markovian quantum systems at low temperature is linked to the geometry of the driving protocol through the quantum (or Fubini-Study) metric. Utilizing these findings, we establish lower bounds on dissipation rates in two-tone protocols, such as those employed for topological frequency conversion. Notably, in appropriate limits these bounds are only determined by the topology of the protocol and an effective quality factor of the system-bath coupling. Our results bridge topological and geometric phenomena with energy dissipation in open quantum systems, and further provide design principles for optimal driving protocols.

关键词： Topology

A Digital quantum Algorithm for Non-Markovian Electron Transfer Dynamics Using Repeated Interactions

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arXiv 2025年

作者： Northcote, Lea K. Teynor, Matthew S. Solomon, Gemma C. NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen ØDK-2100 Denmark Nano-Science Center Department of Chemistry University of Copenhagen Copenhagen ØDK-2100 Denmark

quantum algorithms have the potential to revolutionize our understanding of open quantum systems in chemistry. In this work, we demonstrate that quantum algorithms leveraging a repeated interaction model can effectively reproduce non-Markovian electron transfer processes under four different donor-acceptor parameter regimes and for a donor-bridge-acceptor system. We systematically explore how the algorithm scales for the regimes. Notably, our approach exhibits favorable scaling in the required repeated interaction length as the electronic coupling, temperature, damping rate, and system size increase. Furthermore, a single Trotter step per repeated interaction leads to an acceptably small error, and high-fidelity initial states can be prepared with a short time evolution. This efficiency highlights the potential of the algorithm for tackling increasingly complex systems. When fault-tolerant quantum hardware becomes available, the method could be extended to incorporate structured baths, additional energy levels, or more intricate coupling schemes, enabling the simulation of real-world open quantum systems that remain beyond the reach of classical computation. Copyright © 2025, The Authors. All rights reserved.

关键词： Markov processes

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

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

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Physical Review Research 2025年第2期7卷 023022-023022页

作者： Marco Valentini Rubén Seoane Souto Maksim Borovkov Peter Krogstrup Yigal Meir Martin Leijnse Jeroen Danon Georgios Katsaros Institute of Science and Technology Austria Am Campus 1 3400 Klosterneuburg Austria Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones Científicas (ICMM-CSIC) Madrid 28049 Spain NanoLund and Solid State Physics Lund University Box 118 22100 Lund Sweden Center for Quantum Devices Niels Bohr Institute University of Copenhagen 2100 Copenhagen Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Universitetsparken 5 2100 Copenhagen Denmark Department of Physics Ben-Gurion University of the Negev Beer-Sheva 84105 Israel Department of Physics Norwegian University of Science and Technology NO-7491 Trondheim 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 paper, we study these 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 pierces the superconducting shell. Conversely, in the strong-coupling regime, significant distinctions emerge between the two cases. We attribute this distinct 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.

关键词： quantum optics

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

Machine Learning Enhanced Calculation of quantum-Classical Binding Free Energies

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arXiv 2025年

作者： Bensberg, Moritz Eckhoff, Marco Thomasen, F. Emil Bro-Jørgensen, William Teynor, Matthew S. Sora, Valentina Weymuth, Thomas Husistein, Raphael T. Knudsen, Frederik E. Krogh, Anders Lindorff-Larsen, Kresten Reiher, Markus Solomon, Gemma C. ETH Zurich Department of Chemistry and Applied Biosciences Vladimir-Prelog-Weg 2 Zurich8093 Switzerland University of Copenhagen Department of Biology Linderstrøm-Lang Centre for Protein Science Ole Maaløes Vej 5 Copenhagen NDK-2200 Denmark University of Copenhagen Department of Chemistry and Nano-Science Center Universitetsparken 5 Copenhagen ØDK-2100 Denmark University of Copenhagen Niels Bohr Institute NNF Quantum Computing Programme Blegdamsvej 21 Copenhagen ØDK-2100 Denmark University of Copenhagen Department of Computer Science Universitetsparken 1 Copenhagen ØDK-2100 Denmark Center for Health Data Science Department of Public Health Denmark

Binding free energies are a key element in understanding and predicting the strength of protein–drug interactions. While classical free energy simulations yield good results for many purely organic ligands, drugs including transition metal atoms often require quantum chemical methods for an accurate description. We propose a general and automated workflow that samples the potential energy surface with hybrid quantum mechanics/molecular mechanics (QM/MM) calculations and trains a machine learning (ML) potential on the QM energies and forces to enable efficient alchemical free energy simulations. To represent systems including many different chemical elements efficiently and to account for the different description of QM and MM atoms, we propose an extension of element-embracing atom-centered symmetry functions for QM/MM data as an ML descriptor. The ML potential approach takes electrostatic embedding and long-range electrostatics into account. We demonstrate the applicability of the workflow on the well-studied protein–ligand complex of myeloid cell leukemia 1 and the inhibitor 19G and on the anti-cancer drug NKP1339 acting on the glucose-regulated protein 78. Copyright © 2025, The Authors. All rights reserved.

关键词： Ligands

Hierarchical quantum embedding by machine learning for large molecular assemblies

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arXiv 2025年

作者： Bensberg, Moritz Eckhoff, Marco Husistein, Raphael T. Teynor, Matthew S. Sora, Valentina Bro-Jørgensen, William Thomasen, F. Emil Krogh, Anders Lindorff-Larsen, Kresten Solomon, Gemma C. Weymuth, Thomas Reiher, Markus ETH Zurich Department of Chemistry and Applied Biosciences Vladimir-Prelog-Weg 2 Zurich8093 Switzerland University of Copenhagen Department of Chemistry and Nano-Science Center Universitetsparken 5 Copenhagen ØDK-2100 Denmark University of Copenhagen Niels Bohr Institute NNF Quantum Computing Programme Blegdamsvej 17 Copenhagen ØDK-2100 Denmark University of Copenhagen Department of Computer Science Universitetsparken 1 Copenhagen ØDK-2100 Denmark University of Copenhagen Department of Biology Linderstrøm-Lang Centre for Protein Science Ole Maaløes Vej 5 Copenhagen NDK-2200 Denmark University of Copenhagen Center for Health Data Science Department of Public Health Øster Farimagsgade 5 Copenhagen ØDK-1353 Denmark

We present a quantum-in-quantum embedding strategy coupled to machine learning potentials to improve on the accuracy of quantum-classical hybrid models for the description of large molecules. In such hybrid models, relevant structural regions (such as those around reaction centers or pockets for binding of host molecules) can be described by a quantum model that is then embedded into a classical molecular-mechanics environment. However, this quantum region may become so large that only approximate electronic structure models are applicable. To then restore accuracy in the quantum description, we here introduce the concept of quantum cores within the quantum region that are amenable to accurate electronic structure models due to their limited size. Huzinaga-type projection-based embedding, for example, can deliver accurate electronic energies obtained with advanced electronic structure methods. The resulting total electronic energies are then fed into a transfer learning approach that efficiently exploits the higher-accuracy data to improve on a machine learning potential obtained for the original quantum-classical hybrid approach. We explore the potential of this approach in the context of a well-studied protein-ligand complex for which we calculate the free energy of binding using alchemical free energy and non-equilibrium switching simulations. Copyright © 2025, The Authors. All rights reserved.

关键词： Molecules