Quantum information articles within Nature Communications

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  • Article
    | Open Access

    A promising strategy for scaling trapped-ion-based quantum technologies is to use fully integrated optical waveguides to deliver light to numerous ions at multiple sites. Here, the authors. optically address three ions using on-chip waveguides to deliver three distinct wavelengths per ion, and perform Rabi flopping on each ion simultaneously.

    • Joonhyuk Kwon
    • , William J. Setzer
    •  & Hayden J. McGuinness

  • Article
    | Open Access

    Given that entangled states can store more information than unentangled ones, it would be natural to assume that highly-entangled data would always enhance capabilities of quantum machine learning models. Here, the authors show that this is not the case, in particular when the allowed number of measurements to incoherently learn quantum dynamics is low

    • Xinbiao Wang
    • , Yuxuan Du
    •  & Dacheng Tao

  • Article
    | Open Access

    Understanding loss mechanisms in superconducting circuits is crucial for improving qubit coherence. Here the authors use a multimode resonator to study loss mechanisms in thin-film superconducting circuits and demonstrate on-chip quantum memories with lifetimes exceeding 1ms, using Ta thin-films and high-temperature substrate annealing

    • Suhas Ganjam
    • , Yanhao Wang
    •  & Robert J. Schoelkopf

  • Article
    | Open Access

    Point defects in 2D semiconductors have potential for quantum computing applications, but their controlled design and synthesis remains challenging. Here, the authors identify and fabricate a promising quantum defect in 2D WS2 via high-throughput computational screening and scanning tunnelling microscopy.

    • John C. Thomas
    • , Wei Chen
    •  & Geoffroy Hautier

  • Article
    | Open Access

    Measuring quantum entanglement remains a demanding task. The authors introduce two functions to quantify entanglement induced by fermionic or bosonic statistics, in transport experiments. Both functions, in theory and experiment, are remarkably resilient against the nonuniversal effects of interactions.

    • Gu Zhang
    • , Changki Hong
    •  & Yuval Gefen

  • Article
    | Open Access

    An efficient way of realising a large number of telecom single-photon emitters for quantum communication is still missing. Here, the authors use a wide-field imaging technique for fast localization of single InAs/InP quantum dots, which are then integrated into circular Bragg grating cavities featuring high single-photon purity and indistinguishability.

    • Paweł Holewa
    • , Daniel A. Vajner
    •  & Elizaveta Semenova

  • Article
    | Open Access

    The problem of reversibility within general quantum resource theories is still an open one. Here, the authors prove that a reversible entanglement manipulation framework (and, consequently, the concept of entanglement entropy) can be formally established by adjusting the setting to allow for probabilistic operations

    • Bartosz Regula
    •  & Ludovico Lami

  • Article
    | Open Access

    Entangled local states can be made capable of violating Bell inequalities via nonlocality activation. Typical theoretical approaches require processing many copies of the original state and performing joint measurements on the ensemble. Here, instead, the authors experimentally demonstrate how to do so using a single copy of the state, broadcasting it to two spatially separated parties within a three-node network.

    • Luis Villegas-Aguilar
    • , Emanuele Polino
    •  & Geoff J. Pryde

  • 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

    Solving combinatorial optimization problems using quantum or quantum-inspired machine learning models would benefit from strategies able to work with arbitrary objective functions. Here, the authors use the power of generative models to realise such a black-box solver, and show promising performances on some portfolio optimization examples.

    • Javier Alcazar
    • , Mohammad Ghazi Vakili
    •  & Alejandro Perdomo-Ortiz

  • Article
    | Open Access

    Usual multiqubit entangled states can be described using the graph formalism, where each edge connects only two qubits. Here, instead, the authors use a reprogrammable silicon photonics chip to showcase preparation, verification and processing of arbitrary four-qubit hypergraph states, where hyperedges describe entanglement within a subset of many qubits.

    • Jieshan Huang
    • , Xudong Li
    •  & Jianwei Wang

  • Article
    | Open Access

    Studying bounds on the speed of information propagation across interacting boson systems is notoriously difficult. Here, the authors find tight bounds for both the transport of boson particles and information propagation, for arbitrary time-dependent Bose-Hubbard-type Hamiltonians in arbitrary dimensions.

    • Tomotaka Kuwahara
    • , Tan Van Vu
    •  & Keiji Saito

  • 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

    The ability to characterize large and complex nuclear-spin networks could enable quantum applications, such as quantum simulations of many-body physics. Here the authors develop a high-resolution quantum-sensing method and use it to image a network of 50 nuclear spins surrounding a single NV center in diamond.

    • G. L. van de Stolpe
    • , D. P. Kwiatkowski
    •  & T. H. Taminiau

  • 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

    Detection of topological phases in experiments is challenging, especially in the presence of incoherent noise. Cong et al. introduce a novel method combining error correction and renormalization-group flow and apply it to characterization of quantum spin liquid phases realized in a Rydberg-atom simulator.

    • Iris Cong
    • , Nishad Maskara
    •  & Mikhail D. Lukin

  • 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

    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

    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

    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

    Recent work proposed a machine learning algorithm for predicting ground state properties of quantum many-body systems that outperforms any non-learning classical algorithm but requires extensive training data. Lewis et al. present an improved algorithm with exponentially reduced training data requirements.

    • Laura Lewis
    • , Hsin-Yuan Huang
    •  & John Preskill

  • 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

    Learning Hamiltonians or Lindbladians of quantum systems from experimental data is important for characterization of interactions and noise processes in quantum devices. Here the authors propose an efficient protocol based on estimating time derivatives using multiple temporal sampling points and robust polynomial interpolation.

    • Daniel Stilck França
    • , Liubov A. Markovich
    •  & Johannes Borregaard

  • Article
    | Open Access

    Scalable training of parametrised quantum circuit approaches is usually hindered by the barren plateau issue. Here, the authors show how initializing parametrised quantum circuits starting from scalable tensor-network based algorithms could ameliorate the problem.

    • Manuel S. Rudolph
    • , Jacob Miller
    •  & Alejandro Perdomo-Ortiz

  • Article
    | Open Access

    Remote transport of high-dimensional-encoded photonic states could in principle be achieved via quantum teleportation, but with considerable experimental effort. Here, instead, the authors exploit spatial-mode engineered frequency conversion between a coherent wave packet and a single photon to remotely transfer the HD OAM states, also providing a strategy for quantum imaging.

    • Xiaodong Qiu
    • , Haoxu Guo
    •  & Lixiang Chen

  • 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

    The quantum error-correcting codes formed by tensor network models of holography have so far failed to produce the expected correlation functions in the boundary states. Here, the authors fill this gap by modifying a previously proposed model of hyperinvariant tensor networks.

    • Matthew Steinberg
    • , Sebastian Feld
    •  & Alexander Jahn

  • 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

    Molecular electron spins are promising qubit candidates, however physical implementation of quantum gates is challenging. Little et al. explore the implementation of two-qubit entangling gates between nitroxide spin centres by pulsed electron paramagnetic resonance, building on NMR quantum computing protocols.

    • Edmund J. Little
    • , Jacob Mrozek
    •  & Richard E. P. Winpenny

  • Article
    | Open Access

    Storage of photon entanglement at telecommunication wavelength is an important milestone for the development of the quantum internet. Here, the authors demonstrate storage and retrieval of entangled telecom photons—generated through SWFM in a silicon nitride microring resonator—in an Erbium doped crystal.

    • Ming-Hao Jiang
    • , Wenyi Xue
    •  & Xiao-Song Ma

  • Article
    | Open Access

    Nuclear spins in solid-state systems present a promising platform for quantum information applications. Here the authors report evidence of the long-predicted entangled dark nuclear spin state via optical polarization of localized hole spins coupled to the nuclear bath in a lead halide perovskite semiconductor.

    • E. Kirstein
    • , D. S. Smirnov
    •  & M. Bayer

  • 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

    Our current understanding of the computational abilities of near-intermediate scale quantum (NISQ) computing devices is limited, in part due to the absence of a precise definition for this regime. Here, the authors formally define the NISQ realm and provide rigorous evidence that its capabilities are situated between the complexity classes BPP and BQP.

    • Sitan Chen
    • , Jordan Cotler
    •  & Jerry Li

  • Article
    | Open Access

    Spin defects in semiconductors are promising for quantum technologies but understanding of defect formation processes in experiment remains incomplete. Here the authors present a computational protocol to study the formation of spin defects at the atomic scale and apply it to the divacancy defect in SiC.

    • Cunzhi Zhang
    • , Francois Gygi
    •  & Giulia Galli

  • Article
    | Open Access

    Performing quantum computing in the NISQ era requires reliable information on the gate noise characteristics and their performance benchmarks. Here, the authors show how to estimate the individual noise properties of any quantum process from the noisy eigenvalues of its corresponding quantum channel.

    • Yanwu Gu
    • , Wei-Feng Zhuang
    •  & Dong E. Liu

  • Article
    | Open Access

    Quantum theory allows for indefinite causal order, but experimental demonstrations of such scenarios have so far required trust in the internal functioning of the apparatus. Here, the authors point out a scenario where indefinite causal order could be certified in a device-independent way, if one excludes superluminal and retrocausal influences.

    • Tein van der Lugt
    • , Jonathan Barrett
    •  & Giulio Chiribella

  • 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

    Security proofs against general attacks are the ultimate goal of QKD. Here, the authors show how the Generalised Entropy Accumulation Theorem can be used, for some classes of QKD scenarios, to translate security proofs against collective attacks in the asymptotic regime into proofs against general attacks in the finite-size regime.

    • Tony Metger
    •  & Renato Renner

  • Article
    | Open Access

    In order to be practical, schemes for characterizing quantum operations should require the simplest possible gate sequences and measurements. Here, the authors show how random gate sequences and native measurements (followed by classical post-processing) are sufficient for estimating several gate set properties.

    • J. Helsen
    • , M. Ioannou
    •  & I. Roth

  • Article
    | Open Access

    Continuous-variable quantum networks are easier to implement than discrete-variable ones, but suffer from a lower teleportation fidelity. Here, the authors demonstrate a CV teleportation protocol exploiting heralded noiseless amplification to increase the fidelity, at the expense of probabilistic operation.

    • Jie Zhao
    • , Hao Jeng
    •  & Ping Koy Lam

  • Article
    | Open Access

    Hybrid quantum systems, such as superconducting qubits interacting with microwave photons in resonators, offer a rich platform for exploring fundamental physics. Wang et al. observe parity symmetry breaking in a probe qubit dispersively coupled to a resonator in the deep-strong coupling regime.

    • Shuai-Peng Wang
    • , Alessandro Ridolfo
    •  & J. Q. You

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