Qubits articles within Nature Communications

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  • Article
    | Open Access

    Parity detection is essential in quantum error correction. Here, authors propose a reliable joint parity measurement (JPM) scheme inspired by stimulated emission and experimentally implement the weight-2(4) JPM scheme in a tunable coupling superconducting circuit, which shows comparable performance to the standard CNOT-gate based scheme.

    • Sainan Huai
    • , Kunliang Bu
    •  & Yicong Zheng

  • Article
    | Open Access

    Manipulating quantum information encoded in a bosonic mode requires sizeable and controllable nonlinearities, but superconducting devices’ strong nonlinearities are normally static. Here, the authors use a SNAIL to suppress static nonlinearities and use drive-dependent ones to reach universal control of a bosonic mode.

    • Axel M. Eriksson
    • , Théo Sépulcre
    •  & Simone Gasparinetti

  • Article
    | Open Access

    Ensuring high-fidelity quantum gates while increasing the number of qubits poses a great challenge. Here the authors present a scalable strategy for optimizing frequency trajectories as a form of error mitigation on a 68-qubit superconducting quantum processor, demonstrating high single- and two-qubit gate fidelities.

    • Paul V. Klimov
    • , Andreas Bengtsson
    •  & Hartmut Neven

  • Article
    | Open Access

    Understanding machine learning models’ ability to extrapolate from training data to unseen data - known as generalisation - has recently undergone a paradigm shift, while a similar understanding for their quantum counterparts is still missing. Here, the authors show that uniform generalization bounds pessimistically estimate the performance of quantum machine learning models.

    • Elies Gil-Fuster
    • , Jens Eisert
    •  & Carlos Bravo-Prieto

  • Article
    | Open Access

    Real-time adaptive control of a qubit has been demonstrated but limited to single-axis Hamiltonian estimation. Here the authors implement two-axis control of a singlet-triplet spin qubit with two fluctuating Hamiltonian parameters, resulting in improved quality of coherent oscillations.

    • Fabrizio Berritta
    • , Torbjørn Rasmussen
    •  & Ferdinand Kuemmeth

  • Article
    | Open Access

    Autonomous quantum error correction protects quantum systems against decoherence through engineered dissipation. Here the authors introduce the Star code, which actively corrects single-photon loss and passively suppresses low-frequency dephasing and implement it in a two-transmon device.

    • Ziqian Li
    • , Tanay Roy
    •  & David I. Schuster

  • Article
    | Open Access

    Qudits, higher-dimensional analogues of qubits, expand quantum state space for information processing using fewer physical units. Here the authors demonstrate control over a 16-dimensional Hilbert space, equivalent to four qubits, using combined electron-nuclear states of a single Sb donor atom in Si.

    • Irene Fernández de Fuentes
    • , Tim Botzem
    •  & Andrea Morello

  • Article
    | Open Access

    Electron charge and spin shuttling is a promising technique for connecting distant spin qubits. Here the authors use conveyor-mode shuttling to achieve high-fidelity transport of a single electron spin in Si/SiGe by separation and rejoining of two spin-entangled electrons across a shuttling distance of 560 nm.

    • Tom Struck
    • , Mats Volmer
    •  & Lars R. Schreiber

  • Article
    | Open Access

    Trapped ion quantum systems based on sympathetic cooling use ions of different species. Here the authors demonstrate exchange cooling using two ions of the same species (40Ca+) by taking advantage of the exchange of energy when the ions are brought close together.

    • Spencer D. Fallek
    • , Vikram S. Sandhu
    •  & Kenton R. Brown

  • Article
    | Open Access

    By coupling a spin-qubit to a superconducting resonator, remote spin-entanglement becomes feasible. Here, Ungerer et al achieve strong coupling between a superconducting resonator and a singlet-triplet spin qubit, in an InAs nanowire.

    • J. H. Ungerer
    • , A. Pally
    •  & C. Schönenberger

  • Article
    | Open Access

    Highly polarized nuclear spins can supress decoherence of electron spin qubits, but this requires near-unity polarization. Here the authors implement a protocol combining optical excitation and fast carrier tunnelling to achieve nuclear spin polarizations above 95% in GaAs quantum dots on a timescale of 1 minute.

    • Peter Millington-Hotze
    • , Harry E. Dyte
    •  & Evgeny A. Chekhovich

  • Article
    | Open Access

    Thermal fluctuations can induce ordering in frustrated magnetic systems, yet the impact of quantum fluctuations is less explored. Here, in the controlled environment of a quantum annealer composed of superconducting qubits, the authors study a frustrated magnetic system finding that quantum fluctuations enhance magnetic correlations.

    • Alejandro Lopez-Bezanilla
    • , Andrew D. King
    •  & Avadh Saxena

  • Article
    | Open Access

    Light-matter interfaces implementing arbitrary conditional operations on incoming photons would have several applications in quantum computation and communications. Here, the authors demonstrate conditional polarization rotation induced by a single quantum dot spin embedded in an electrically contacted micropillar, spanning up to a pi flip.

    • E. Mehdi
    • , M. Gundín
    •  & L. Lanco

  • Article
    | Open Access

    It is still unclear whether and how quantum computing might prove useful in solving known large-scale classical machine learning problems. Here, the authors show that variants of known quantum algorithms for solving differential equations can provide an advantage in solving some instances of stochastic gradient descent dynamics.

    • Junyu Liu
    • , Minzhao Liu
    •  & Liang Jiang

  • Article
    | Open Access

    Efficient characterisation of quantum many-body Hamiltonians has important applications for benchmarking NISQ devices. Here, the authors propose a method employing Chebyshev regression to learn the full Hamiltonian of a quantum system, with a sample complexity that scales efficiently with the system size.

    • Andi Gu
    • , Lukasz Cincio
    •  & Patrick J. Coles

  • Article
    | Open Access

    Isotope engineering can enhance spin coherence of solid-state defects, such as NV centers in diamond but progress for defects in hBN has been limited. Gong et al. report the optimization of isotopes in hBN and demonstrate improved coherence and relaxation times for the negatively charged boron vacancy centers.

    • Ruotian Gong
    • , Xinyi Du
    •  & Chong Zu

  • Article
    | Open Access

    Graphene quantum dots promise applications for spin and valley qubits; however a demonstration of phase coherent oscillations has been lacking. Here the authors report coherent charge oscillations and measurements of coherence times in highly tuneable double quantum dots in bilayer graphene.

    • K. Hecker
    • , L. Banszerus
    •  & C. Stampfer

  • Article
    | Open Access

    It has been conjectured that an alternative model of quantum computation—in which one only applies two-qubit singlet-vs-triplet measurements to almost any source of input qubits—is as powerful as the usual gate-based model. Here, the authors prove this conjecture, ending up with a model where computations are independent from the way in which one picks the axes of the Bloch sphere.

    • Terry Rudolph
    •  & Shashank Soyuz Virmani

  • Article
    | Open Access

    Real-time feedback control of quantum systems without relying on a description of the system itself is usually challenging. Here, the authors exploit deep reinforcement learning to realise feedback control for initialisation of a superconducting qubit on a submicrosecond timescale.

    • Kevin Reuer
    • , Jonas Landgraf
    •  & Christopher Eichler

  • Article
    | Open Access

    In order to be useful for future large-scale quantum computing, quantum error correction needs to allow for fast enough classical decoding time, while at the moment the slowdown is exponential in the size of the code. Here, the authors remove this roadblock, showing how to parallelize decoding and make the slowdown polynomial.

    • Luka Skoric
    • , Dan E. Browne
    •  & Earl T. Campbell

  • Article
    | Open Access

    Schrodinger’s cat states constitute an important resource for quantum information processing, but present challenges in terms of scalabilty and controllability. Here, the authors exploit fast Kerr nonlinearity modulation to generate and store cat states in superconducting circuits in a more scalable way.

    • X. L. He
    • , Yong Lu
    •  & Z. R. Lin

  • Article
    | Open Access

    Circuit QED with strongly driven cavities is a powerful framework for quantum technologies, but often undesired effects on the qubit are introduced. Here, by using an external tone tailored to destructively interfere with the cavity field, the authors show how a transmon can be protected from these unwanted effects.

    • Cristóbal Lledó
    • , Rémy Dassonneville
    •  & Alexandre Blais

  • Article
    | Open Access

    The beamsplitter operation is a key component for quantum information processing, but implementations in superconducting circuit-QED usually introduce additional decoherence. Here, the authors exploit the symmetry within a SQUID, driven in a purely differential manner, to realise clean BS operations between two SC cavity modes.

    • Yao Lu
    • , Aniket Maiti
    •  & Robert J. Schoelkopf

  • Article
    | Open Access

    Quantum simulations of topological matter with superconducting qubits have been attracting attention recently. Xiang et al. realize 2D and bilayer Chern insulators with synthetic dimensions on a programmable 30-qubit-ladder superconducting processor, showing bulk-boundary correspondence.

    • Zhong-Cheng Xiang
    • , Kaixuan Huang
    •  & Heng Fan

  • Article
    | Open Access

    Negatively-charged boron vacancy centers in hBN have short coherence times, hindering their potential as quantum sensors. By employing dynamical decoupling, the authors achieve an ensemble coherence time approaching the fundamental relaxation limit, enabling sensitive detection of MHz range electromagnetic fields.

    • Roberto Rizzato
    • , Martin Schalk
    •  & Dominik B. Bucher

  • Article
    | Open Access

    Single-shot readout of optically active spin qubits is typically limited by low photon collection rates and measurement back-action. Here the authors overcome these limitations by using an open cavity approach for single-shot readout of a semiconductor quantum dot and demonstrate record readout time of a few ns.

    • Nadia O. Antoniadis
    • , Mark R. Hogg
    •  & Richard J. Warburton

  • Article
    | Open Access

    Hybrid quantum acoustic systems integrating qubits with phonons offer a novel platform for investigating open quantum systems. Kitzman et al. report control of superposition states of a transmon qubit under the effect of drive and dissipation by engineering its coupling to a bath of surface acoustic wave phonons.

    • J. M. Kitzman
    • , J. R. Lane
    •  & J. Pollanen

  • Article
    | Open Access

    As the size of quantum processors scales up, accurate characterization of errors due to various crosstalks between qubits becomes important. Here the authors use a novel benchmarking protocol to study single-gate fidelities in a 2x2 hole spin qubit array in germanium when qubits are driven simultaneously.

    • W. I. L. Lawrie
    • , M. Rimbach-Russ
    •  & M. Veldhorst

  • Article
    | Open Access

    Removing excess energy (cooling) and reducing noise in superconducting quantum circuits is central to improved coherence. Lucas et al. demonstrate cooling of a superconducting resonator and its noisy environment to sub-mK temperatures by immersion in liquid 3He.

    • M. Lucas
    • , A. V. Danilov
    •  & S. E. de Graaf

  • Article
    | Open Access

    The boron vacancy center in hBN has been intensively studied, but its characterizations have remained limited. Here the authors achieve a 5-fold enhancement of coherence time using dynamical decoupling, which enables the direct estimation of defect concentration and its electric field susceptibility.

    • Ruotian Gong
    • , Guanghui He
    •  & Chong Zu

  • Article
    | Open Access

    Wigner molecules, or correlated localized electron states, has been reported in semiconductor quantum dots, but their interaction with environment has been less explored. Here the authors use the spin multiplet structure of a three-electron Wigner molecule to enhance and control dynamic nuclear polarization.

    • Wonjin Jang
    • , Jehyun Kim
    •  & Dohun Kim

  • Article
    | Open Access

    Interaction between localized electron spins and nuclear spins causes shifts in nuclear spin energy levels, but how this affects nuclear spin diffusion in quantum dots is not fully understood. Here the authors show that the central electron accelerates nuclear spin diffusion in GaAs/AlGaAs quantum dots.

    • Peter Millington-Hotze
    • , Santanu Manna
    •  & Evgeny A. Chekhovich

  • Article
    | Open Access

    Encoding quantum information in qudits instead of qubits allows for several advantages, but scalable native entangling techniques would be needed. Here, the authors show how to use light-shift gates to perform entangling operations on trapped ion systems, with a calibration overhead which is independent on the qudit dimension.

    • Pavel Hrmo
    • , Benjamin Wilhelm
    •  & Martin Ringbauer

  • Article
    | Open Access

    It has been predicted that entanglement phase diagrams of Haar-measure random states can show interesting phenomenology, including entanglement phase transitions. Here, the authors confirm these predictions using up to 15 qubits in a fully-connected superconducting quantum processor.

    • Tong Liu
    • , Shang Liu
    •  & Heng Fan

  • Article
    | Open Access

    Understanding phonon-induced relaxation in molecular qubits is a crucial step in realizing their application potential. Garlatti at al. use a combination of inelastic X-ray scattering and density functional theory to investigate the role of low-energy phonons on spin relaxation of a prototypical molecular qubit.

    • E. Garlatti
    • , A. Albino
    •  & S. Carretta

  • Article
    | Open Access

    Fusion gates are common operations in photonic quantum information platforms, where they are employed to create entanglement. Here, the authors propose a quantum computation scheme where the same measurements used to generate entanglement can also be used to achieve fault-tolerance leading to an increased tolerance to errors.

    • Sara Bartolucci
    • , Patrick Birchall
    •  & Chris Sparrow

  • Article
    | Open Access

    Spins defined in single-walled carbon nanotubes promise ultra-long spin relaxation times, but qubit implementations require confinement of isolated spins. Here the authors report highly confined long-lived electron spins in chemically functionalized nanotubes and demonstrate their coherent control.

    • Jia-Shiang Chen
    • , Kasidet Jing Trerayapiwat
    •  & Xuedan Ma

  • Article
    | Open Access

    A possible route to scalability of trapped-ion-based quantum computing platforms is to connect multiple modules where ions can be shuttled across different registers. Here, the authors demonstrate fast and low-loss transfer of trapped ions between two microchip modules.

    • M. Akhtar
    • , F. Bonus
    •  & W. K. Hensinger

  • Article
    | Open Access

    Spin defects in 2D hBN are promising for magnetic field sensing but suffer from short spin coherence times. Here the authors extend the coherence time for an ensemble of spins in hBN to 4 microseconds by using a continuous microwave drive and demonstrate qubit control in a protected spin space.

    • Andrew J. Ramsay
    • , Reza Hekmati
    •  & Isaac J. Luxmoore

  • Article
    | Open Access

    Computational search for defect centers in semiconductors typically assumes that the defects realize the most thermodynamically stable configuration. Here the authors demonstrate, for a complex defect in silicon, that this is not always the case if the kinetics of defect formation is taken into account.

    • Peter Deák
    • , Péter Udvarhelyi
    •  & Adam Gali

  • Article
    | Open Access

    Spin qubits in Si/SiGe quantum dots suffer from variability in the valley splitting which will hinder device scalability. Here, by using 3D atomic characterization, the authors explain this variability by random Si and Ge atomic fluctuations and propose a strategy to statistically enhance the valley splitting

    • Brian Paquelet Wuetz
    • , Merritt P. Losert
    •  & Giordano Scappucci

  • Article
    | Open Access

    Qutrits, or quantum three-level systems, can provide advantages over qubits in certain quantum information applications, and high-fidelity single-qutrit gates have been demonstrated. Goss et al. realize high-fidelity entangling gates between two superconducting qutrits that are universal for ternary computation.

    • Noah Goss
    • , Alexis Morvan
    •  & Irfan Siddiqi

  • Article
    | Open Access

    Quasiparticles, or broken Cooper pairs, are a major source of decoherence in superconducting qubits but their origin is debated. Pan et al. confirm the dominant mechanism due to photon absorption in the Josephson junction and demonstrate mitigation strategies based on tuning of the qubit geometry.

    • Xianchuang Pan
    • , Yuxuan Zhou
    •  & Dapeng Yu

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