Information theory and computation

  • Article
    | Open Access

    Several key tasks in quantum information processing can be regarded as channel manipulation. Here, focusing on the class of distillation protocols, the authors derive general bounds on resource overhead and incurred errors, showing application to magic state distillation and quantum channel capacities.

    • Bartosz Regula
    •  & Ryuji Takagi
  • Article
    | Open Access

    Parametrised quantum circuits are a promising hybrid classical-quantum approach, but rigorous results on their effective capabilities are rare. Here, the authors explore the feasibility of training depending on the type of cost functions, showing that local ones are less prone to the barren plateau problem.

    • M. Cerezo
    • , Akira Sone
    •  & Patrick J. Coles
  • Article
    | Open Access

    Theoretical aspects of automated learning from data involving deep neural networks have open questions. Here Giambagli et al. show that training the neural networks in the spectral domain of the network coupling matrices can reduce the amount of learning parameters and improve the pre-training process.

    • Lorenzo Giambagli
    • , Lorenzo Buffoni
    •  & Duccio Fanelli
  • Article
    | Open Access

    Many mean-field theories are proposed for studying the non-equilibrium dynamics of complex systems, each based on specific assumptions about the system’s temporal evolution. Here, Aguilera et al. propose a unified framework for mean-field theories of asymmetric kinetic Ising systems to study non-equilibrium dynamics.

    • Miguel Aguilera
    • , S. Amin Moosavi
    •  & Hideaki Shimazaki
  • Article
    | Open Access

    Phase diagrams describe how a system changes phenomenologically as an external parameter, such as a magnetic field strength, is varied. Here, the authors prove that in general such a phase diagram is uncomputable, by explicitly constructing a one-parameter Hamiltonian for which this is the case.

    • Johannes Bausch
    • , Toby S. Cubitt
    •  & James D. Watson
  • Article
    | Open Access

    Coupled donor wavefunctions in silicon are spatially resolved to evidence valley interference processes. An atomic-scale understanding of the interplay between interference, envelope anisotropy and crystal symmetries unveils a placement strategy compatible with existing technology where the exchange is insensitive to interference.

    • B. Voisin
    • , J. Bocquel
    •  & S. Rogge
  • Article
    | Open Access

    Typically, Boolean logic gates have to compromise between high speed and low energy consumption which can become limiting at scale. Here, the authors demonstrate architectures for NOT and XNOR gates that enable simultaneous low power and fast operation.

    • Reza Maram
    • , James van Howe
    •  & José Azaña
  • Article
    | Open Access

    Time-dependent errors are one of the main obstacles to fully-fledged quantum information processing. Here, the authors develop a general methodology to monitor time-dependent errors, which could be used to make other characterisation protocols time-resolved, and demonstrate it on a trapped-ion qubit.

    • Timothy Proctor
    • , Melissa Revelle
    •  & Kevin Young
  • Article
    | Open Access

    According to Zipf’s law, the population size of a city is inversely proportional to its size rank in any urban system. The authors show how demography explains this law as a time average of balanced migration between cities and how deviations express information about people’s net preferences.

    • Luís M. A. Bettencourt
    •  & Daniel Zünd
  • Article
    | Open Access

    The no-signaling principle constrains which multipartite correlations are allowed, but network scenarios considered so far were limited to specific cases. Here, the authors apply inflation technique to the no-input/binary-output triangle network, and show that it admits non-trilocal distributions.

    • Nicolas Gisin
    • , Jean-Daniel Bancal
    •  & Nicolas Brunner
  • Article
    | Open Access

    Fault-tolerant quantum computation is still far, but there could be ways in which quantum error correction could improve currently available devices. Here, the authors show how to exploit existing quantum codes through only post-processing and random measurements in order to mitigate errors in NISQ devices.

    • Jarrod R. McClean
    • , Zhang Jiang
    •  & Hartmut Neven
  • Article
    | Open Access

    Quantum error mitigation promises to improve expectation values’ estimation without the resource overhead of quantum error correction. Here, the authors test probabilistic error cancellation using trapped ions, decreasing single- and two-qubit gates’ error rates by two and one order of magnitude respectively.

    • Shuaining Zhang
    • , Yao Lu
    •  & Kihwan Kim
  • Article
    | Open Access

    There is a lack of systematic approaches to identify and analyze the hierarchical structure of geo-industrial clusters at the global scale. Here the authors use LinkedIn's employment history data to construct a global labor flow network from which they find that the resulting geo-industrial clusters exhibit a stronger association between the influx of educated-workers and financial performance compared to existing aggregation units.

    • Jaehyuk Park
    • , Ian B. Wood
    •  & Yong-Yeol Ahn
  • Article
    | Open Access

    The Consistent Histories formalism can solve paradoxes in quantum mechanics, but finding such consistent sets of histories requires a computational overhead which is exponential in the problem’s size. Here, the authors report a variational hybrid algorithm solving this problem using polynomial resources.

    • Andrew Arrasmith
    • , Lukasz Cincio
    •  & Patrick J. Coles
  • Article
    | Open Access

    The presence of correlations can strongly affect the evolution of a quantum system. Here, the authors directly observe differences in the dynamics of two spins-1/2 systems in an NMR setup depending on the correlations of the initial state, including differences in energy flow and mutual information.

    • Kaonan Micadei
    • , John P. S. Peterson
    •  & Eric Lutz
  • Article
    | Open Access

    Deterministic maps from initial to final states can always be modelled using the master equation formalism, provided additional “hidden” states are available. Here, the authors demonstrate a tradeoff between the required number of such states and the number of required, suitably defined “hidden time steps”.

    • David H. Wolpert
    • , Artemy Kolchinsky
    •  & Jeremy A. Owen
  • Article
    | Open Access

    Continuous-time computation paradigm could represent a viable alternative to the standard digital one when dealing with certain classes of problems. Here, the authors propose a generalised version of a continuous-time solver and simulate its performances in solving MaxSAT and two-colour Ramsey problems.

    • Botond Molnár
    • , Ferenc Molnár
    •  & Mária Ercsey-Ravasz
  • Article
    | Open Access

    With the rapid development of quantum computers, quantum machine learning approaches are emerging as powerful tools to perform electronic structure calculations. Here, the authors develop a quantum machine learning algorithm, which demonstrates significant improvements in solving quantum many-body problems.

    • Rongxin Xia
    •  & Sabre Kais
  • Article
    | Open Access

    The minimal amount of assumptions to justify the use of maximum-entropy ensembles is still debated. Here, the authors show that the transitions that a partially known system environment can undergo are the same allowed for the maximum entropy state which is compatible with the known information.

    • Paul Boes
    • , Henrik Wilming
    •  & Rodrigo Gallego
  • Article
    | Open Access

    Algorithmic information theory measures the complexity of strings. Here the authors provide a practical bound on the probability that a randomly generated computer program produces a given output of a given complexity and apply this upper bound to RNA folding and financial trading algorithms.

    • Kamaludin Dingle
    • , Chico Q. Camargo
    •  & Ard A. Louis
  • Article
    | Open Access

    The security of DIQKD is difficult to prove, as one needs to take into account every possible attack strategy. Here, the authors develop a method to determine the entropy of a system as the sum of the entropies of its parts. Applied to DIQKD, this implies that it suffices to consider i.i.d. attacks.

    • Rotem Arnon-Friedman
    • , Frédéric Dupuis
    •  & Thomas Vidick
  • Article
    | Open Access

    The large data generated in heavy-ion collision experiments require careful analysis to understand the physics. Here the authors use the deep-learning method to sort equation of states in QCD transition and analyze the simulated data sets mimicking the heavy-ion collision experiments.

    • Long-Gang Pang
    • , Kai Zhou
    •  & Xin-Nian Wang
  • Article
    | Open Access

    Estimating the quantum capacity allows one to assess the performance of quantum memories, communication channels, repeaters as well as error correction schemes. Here, the authors show how to estimate and verify one-shot quantum capacity in the most general case of arbitrarily correlated errors.

    • Corsin Pfister
    • , M. Adriaan Rol
    •  & Stephanie Wehner
  • Article
    | Open Access

    In presence of inter-system correlations, violations of the laws of thermodynamics become possible. Here, the authors develop a formalism redefining heat, work and thermodynamic laws in terms of quantum conditional entropy, which consistently generalize thermodynamics in correlated scenarios.

    • Manabendra N. Bera
    • , Arnau Riera
    •  & Andreas Winter
  • Article
    | Open Access

    Operational paradigms for distributed quantum and classical information processing involve multiple rounds of public communication. Here the authors consider the minimum number of communication rounds needed to perform the locality-constrained task of entanglement transformation.

    • Eric Chitambar
    •  & Min-Hsiu Hsieh
  • Article
    | Open Access

    Grover’s algorithm provides a quantum speedup when searching through an unsorted database. Here, the authors perform it on 3 qubits using trapped ions, demonstrating two methods for marking the correct result in the algorithm’s oracle and providing data for searches yielding 1 or 2 solutions.

    • C. Figgatt
    • , D. Maslov
    •  & C. Monroe
  • Article
    | Open Access

    Mapping complex networks to underlying geometric spaces can help understand the structure of networked systems. Here the authors propose a class of machine learning algorithms for efficient embedding of large real networks to the hyperbolic space, with potential impact on big network data analysis.

    • Alessandro Muscoloni
    • , Josephine Maria Thomas
    •  & Carlo Vittorio Cannistraci
  • Article
    | Open Access

    Quantum compressed sensing can provide a scalable way to characterize quantum states and devices, but has been so far limited to states with quickly decaying eigenvalues. Here the authors show that it can be appropriate even in the general case, demonstrating reconstruction the state of a seven-qubit system.

    • C. A. Riofrío
    • , D. Gross
    •  & J. Eisert
  • Article
    | Open Access

    Solutions of computations can be encoded in the ground state of many-body spin models. Here the authors show that solutions to generic reversible classical computations can be encoded in the ground state of a vertex model, which can be reached without finite temperature phase transitions.

    • C. Chamon
    • , E. R. Mucciolo
    •  & Z.-C. Yang
  • Article
    | Open Access

    Quantum communications will be used to transmit entanglement and secure keys, but it is important to estimate their optimal transfer rates. Here the authors compute the fundamental limit of repeaterless quantum communications for the most relevant practical scenario.

    • Stefano Pirandola
    • , Riccardo Laurenza
    •  & Leonardo Banchi
  • Article
    | Open Access

    Controlling acoustic fields is of interest for diverse applications. Here the authors develop metasurfaces using a small set of pre-manufactured three-dimensional unit cells, quantized in both the spatial and phase domains, achieving with them acoustic levitation.

    • Gianluca Memoli
    • , Mihai Caleap
    •  & Sriram Subramanian
  • Article
    | Open Access

    The K-satisfability problem is a combinatorial discrete optimization problem, which for K=3 is NP-complete, and whose random formulation is of interest for understanding computational complexity. Here, the authors introduce the backtracking survey propagation algorithm for studying it for K=3 and K=4.

    • Raffaele Marino
    • , Giorgio Parisi
    •  & Federico Ricci-Tersenghi
  • Article
    | Open Access

    Zero-knowledge proofs can be used to prove that a statement is true without revealing why it is. Here the authors demonstrate a non-electronic fast neutron radiography technique to confirm that two objects are identical without revealing any details about their design or composition.

    • Sébastien Philippe
    • , Robert J. Goldston
    •  & Francesco d’Errico
  • Article |

    Interacting quantum many-body systems in low dimensions is an active research area in ultra-cold gases. Here, Chomaz et al.study the dimensional crossover of Bose–Einstein condensation and observe the emergence of phase coherence in an ultra-cold quasi-2D Bose gas confined to a flat-bottom trapping potential.

    • Lauriane Chomaz
    • , Laura Corman
    •  & Jean Dalibard
  • Article
    | Open Access

    One mystery of glass transition from supercooled liquid is the lack of apparent change in structure, which is in contrast to a large change in dynamics. Here Dunleavy et al. provide a possible solution to this discrepancy by simulating dynamic correlation using a mutual information approach.

    • Andrew J. Dunleavy
    • , Karoline Wiesner
    •  & C. Patrick Royall
  • Article
    | Open Access

    A disturbance in the local magnetic order can propagate across a material just like a wave. Chumak et al.now demonstrate a transistor operating on a single quantum of these so-called spin waves, known as a magnon, which could be a central element for magnetic-material-based information processing.

    • Andrii V. Chumak
    • , Alexander A. Serga
    •  & Burkard Hillebrands
  • Review Article |

    Computer memory based on ferroelectric polarization is a promising alternative to technologies based, for example, on magnetism. Here, Garcia and Bibes review how ferroelectric tunnel junctions, where ferroelectric polarization controls electrical resistance, could improve the performance of these devices.

    • Vincent Garcia
    •  & Manuel Bibes