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Transforming graph states via Bell state measurements

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arXiv 2024年

作者： Löbl, Matthias C. Pettersson, Love A. Paesani, Stefano Sørensen, Anders S. The Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark

Graph states are key resources for measurement-based quantum computing which is particularly promising for photonic systems. Fusions are probabilistic Bell state measurements, measuring pairs of parity operators of two qubits. Fusions can be used to connect/entangle different graph states making them a powerful resource for measurement-based and the related fusion-based quantum computing. There are several different graph structures and types of Bell state measurements, yet the associated graph transformations have only been analyzed for a few specific cases. Here, we provide a full set of such graph transformation rules and we give an intuitive visualization based on Venn diagrams of local neighborhoods of graph nodes. We derive these graph transformations for all fusion types showing that there are five different types of fusion success cases. Finally, we give application examples of the derived graph transformation rules and show that they can be used for constructing graph codes or simulating fusion networks. Copyright © 2024, The Authors. All rights reserved.

关键词： Graph theory

Efficient percolation simulations for lossy photonic fusion networks

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arXiv 2023年

作者： Löbl, Matthias C. Paesani, Stefano Sørensen, Anders S. The Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark

The study of percolation phenomena has various applications ranging from social networks or materials science to quantum information. The most common percolation models are bond- or site-percolation for which the Newman-Ziff algorithm enables an efficient simulation. Here, we consider several non-standard percolation models that appear in the context of measurement-based photonic quantum computing with so-called graph states and fusion networks. The associated percolation thresholds determine the tolerance to photon loss in such systems and we develop modifications of the Newman-Ziff algorithm to perform the corresponding percolation simulation efficiently. We demonstrate our algorithms by using them to characterize exemplary fusion networks and graph states. The used source code is provided as an open-source repository. Copyright © 2023, The Authors. All rights reserved.

关键词： Percolation (computer storage)

Self-correcting GKP qubit and gates in a driven-dissipative circuit

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arXiv 2024年

作者： Nathan, Frederik O’Brien, Liam Noh, Kyungjoo Matheny, Matthew H. Grimsmo, Arne L. Jiang, Liang Refael, Gil Center for Quantum Devices and NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Department of Physics Institute for Quantum Information and Matter California Institute of Technology PasadenaCA91125 United States AWS Center for Quantum Computing PasadenaCA91125 United States Pritzker School of Molecular Engineering The University of Chicago ChicagoIL60637 United States

We propose a circuit architecture for a dissipatively error-corrected GKP qubit. The device consists of a high-impedance LC circuit coupled to a Josephson junction and a resistor via a controllable switch. When the switch is activated via a particular family of stepwise protocols, the resistor absorbs all noise-induced entropy, resulting in dissipative error correction of both phase and amplitude errors. This leads to an exponential increase of qubit lifetime, reaching beyond 10ms in simulations with near-feasible parameters. We show that the lifetime remains exponentially long in the presence of extrinsic noise and device/control imperfections (e.g., due to parasitics and finite control bandwidth) under specific thresholds. In this regime, lifetime is likely only limited by phase slips and quasiparticle tunneling. We show that the qubit can be read out and initialized via measurement of the supercurrent in the Josephson junction. We finally show that the qubit supports native self-correcting single-qubit Clifford gates, where dissipative error-correction of control noise leads to exponential suppression of gate infidelity. Copyright © 2024, The Authors. All rights reserved.

关键词： Resistors

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

Breadth-first graph traversal union-find decoder

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arXiv 2024年

作者： Löbl, Matthias C. Chen, Susan X. Paesani, Stefano Sørensen, Anders S. The Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark Quantum Engineering Centre for Doctoral Training University of Bristol Bristol United Kingdom NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark

Fast decoding algorithms are decisive for real-time quantum error correction and for analyzing properties of error correction codes. Here, we develop variants of the union-find decoder that simplify its implementation and provide potential decoding speed advantages. Furthermore, we show how these methods can be adapted to decode non-topological quantum lowdensity- parity-check (qLDPC) codes. All the developed decoders can directly include both qubit erasures and Pauli errors in the decoding step, thus addressing the dominant noise mechanisms for photonic quantum computing. We investigate the strengths and weaknesses of the different decoder variants, benchmark their speed and threshold error rates on several codes, and provide the used source code. Copyright © 2024, The Authors. All rights reserved.

关键词： quantum computers

Superconducting Proximity Effect in Two-Dimensional Hole Gases

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arXiv 2024年

作者： Babkin, Serafim Joecker, Benjamin Flensberg, Karsten Serbyn, Maksym Danon, Jeroen Am Campus 1 Klosterneuburg3400 Austria Center for Quantum Devices Niels Bohr Institute University of Copenhagen CopenhagenDK-2100 Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Department of Physics Norwegian University of Science and Technology TrondheimNO-7491 Norway

Technology involving hybrid superconductor–semiconductor materials is a promising avenue for engineering quantum devices for information storage, manipulation, and transmission. Proximity-induced superconducting correlations are an essential part of such devices. While the proximity effect in the conduction band of common semiconductors is well understood, its manifestation in confined hole gases, realized for instance in germanium, is an active area of research. Lower-dimensional hole-based systems, particularly in germanium, are emerging as an attractive platform for a variety of solid-state quantum devices, due to their combination of efficient spin and charge control and long coherence times. The recent experimental realization of the proximity effect in germanium thus calls for a theoretical description that is tailored to hole gases. In this work, we propose a simple model to describe proximity-induced superconductivity in two-dimensional hole gases, incorporating both the heavy-hole (HH) and light-hole (LH) bands. We start from the Luttinger–Kohn model, introduce three parameters that characterize hopping across the superconductor–semiconductor interface, and derive explicit intraband and interband effective pairing terms for the HH and LH bands. Unlike previous approaches, our theory provides a quantitative relationship between induced pairings and interface properties. Restricting our general model to an experimentally relevant case where only the HH band crosses the chemical potential, we predict the coexistence of s-wave and d-wave singlet pairings, along with triplet-type pairings, and modified Zeeman and Rashba spin–orbit couplings. Our model thus presents a starting point for theoretical modeling of quantum devices based on proximitized hole gases, fueling further progress in quantum technology. Copyright © 2024, The Authors. All rights reserved.

关键词： Shear waves

Multiphoton quantum simulation of the generalized Hopfield memory model

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arXiv 2025年

作者： Zanfardino, Gennaro Paesani, Stefano Leuzzi, Luca Santagati, Raffaele Illuminati, Fabrizio Ruocco, Giancarlo Leonetti, Marco Dipartimento di Ingegneria Industriale Università degli Studi di Salerno Via Giovanni Paolo II 132 SA Fisciano84084 Italy Institute of Nanotechnology of the National Research Council of Italy CNR-NANOTEC Rome Unit Piazzale A. Moro 5 RomeI-00185 Italy INFN Sezione di Napoli Gruppo Collegato di Salerno Italy NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Blegdamsvej 17 Copenhagen ØDK-2100 Denmark The Niels Bohr Institute University of Copenhagen Copenhagen ØDK-2100 Denmark Department of Physics Sapienza University of Rome Piazzale A. Moro 5 RomeI-00185 Italy Quantum Lab Boehringer Ingelheim Ingelheim am Rhein55218 Germany Institute of Nanotechnology of the National Research Council of Italy CNR-NANOTEC Lecce Central Unit c/o Campus Ecotekne Via Monteroni Lecce73100 Italy Center for Life Nano- & Neuro-Science Italian Institute of Technology IIT Rome Italy

In the present work, we introduce, develop, and investigate a connection between multiphoton quantum interference, a core element of emerging photonic quantum technologies, and Hopfield-like Hamiltonians of classical neural networks, the paradigmatic models for associative memory and machine learning in systems of artificial intelligence. Specifically, we show that combining a system composed of Nph indistinguishable photons in superposition over M field modes, a controlled array of M binary phase-shifters, and a linear-optical interferometer, yields output photon statistics described by means of a p-body Hopfield Hamiltonian of M Ising-like neurons ±1, with p = 2Nph. We investigate in detail the generalized 4-body Hopfield model obtained through this procedure and show that it realizes a transition from a memory retrieval to a memory black-out regime, i.e. a spin-glass phase, as the amount of stored memory increases. The mapping enables novel routes to the realization and investigation of disordered and complex classical systems via efficient photonic quantum simulators, as well as the description of aspects of structured photonic systems in terms of classical spin Hamiltonians. © 2025, CC BY.

关键词： Hamiltonians

Gatemon Qubit Revisited for Improved Reliability and Stability

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arXiv 2024年

作者： Feldstein-Bofill, David Sun, Zhenhai Wied, Casper Singh, Shikhar Isakov, Brian D. Krøjer, Svend Hastrup, Jacob Gyenis, András Kjaergaard, Morten Center for Quantum Devices Niels Bohr Institute University of Copenhagen Denmark NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Department of Electrical Computer & Energy Engineering University of Colorado Boulder BoulderCO80309 United States Department of Physics University of Colorado Boulder BoulderCO80309 United States

The development of quantum circuits based on hybrid superconductor-semiconductor Josephson junctions holds promise for exploring their mesoscopic physics and for building novel superconducting devices. The gate-tunable superconducting transmon qubit (gatemon) is the paradigmatic example of such a superconducting circuit. However, gatemons typically suffer from unstable and hysteretic qubit frequencies with respect to the applied gate voltage and reduced coherence times. Here we develop methods for characterizing these challenges in gatemons and deploy these methods to compare the impact of shunt capacitor designs on gatemon performance. Our results indicate a strong frequency- and design-dependent behavior of the qubit stability, hysteresis, and dephasing times. Moreover, we achieve highly reliable tuning of the qubit frequency with 1 MHz precision over a range of several GHz, along with improved stability in grounded gatemons compared to gatemons with a floating capacitor design. © 2024, CC BY.

关键词： Qubits

Dynamical Polarization of the Fermion Parity in a Nanowire Josephson Junction

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Physical Review Letters 2023年第11期131卷 117001-117001页

作者： J. J. Wesdorp L. Grünhaupt A. Vaartjes M. Pita-Vidal A. Bargerbos L. J. Splitthoff P. Krogstrup B. van Heck G. de Lange QuTech and Kavli Institute of Nanoscience Delft University of Technology 2628 CJ Delft Netherlands NNF Quantum Computing Programme Niels Bohr Institute University of Copenhagen Denmark Microsoft Quantum Lab Delft 2628 CJ Delft Netherlands Leiden Institute of Physics Universiteit Leiden Niels Bohrweg 2 2333 CA Leiden Netherlands Dipartimento di Fisica Sapienza Università di Roma P.le Aldo Moro 2 00185 Roma Italy

Josephson junctions in InAs nanowires proximitized with an Al shell can host gate-tunable Andreev bound states. Depending on the bound state occupation, the fermion parity of the junction can be even or odd. Coherent control of Andreev bound states has recently been achieved within each parity sector, but it is impeded by incoherent parity switches due to excess quasiparticles in the superconducting environment. Here, we show that we can polarize the fermion parity dynamically using microwave pulses by embedding the junction in a superconducting LC resonator. We demonstrate polarization up to 94%±1% (89%±1%) for the even (odd) parity as verified by single shot parity readout. Finally, we apply this scheme to probe the flux-dependent transition spectrum of the even or odd parity sector selectively, without any postprocessing or heralding.

关键词： Andreev reflection Josephson effect quantum information with hybrid systems Topological superconductors Josephson junctions Nanowires SQUID Semiconductors Superconducting devices Microwave techniques