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Open Access


Article
 Open AccessEvent generation and statistical sampling for physics with deep generative models and a density information buffer
Here, the authors report buffereddensity variational autoencoders for the generation of physical events. This method is computationally less expensive over other traditional methods and beyond accelerating the data generation process, it can help to steer the generation and to detect anomalies.
 Sydney Otten
 , Sascha Caron
 & Rob Verheyen

Article
 Open AccessCost function dependent barren plateaus in shallow parametrized quantum circuits
Parametrised quantum circuits are a promising hybrid classicalquantum 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 AccessMachine learning in spectral domain
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 pretraining process.
 Lorenzo Giambagli
 , Lorenzo Buffoni
 & Duccio Fanelli

Article
 Open AccessA unifying framework for meanfield theories of asymmetric kinetic Ising systems
Many meanfield theories are proposed for studying the nonequilibrium dynamics of complex systems, each based on specific assumptions about the system’s temporal evolution. Here, Aguilera et al. propose a unified framework for meanfield theories of asymmetric kinetic Ising systems to study nonequilibrium dynamics.
 Miguel Aguilera
 , S. Amin Moosavi
 & Hideaki Shimazaki

Article
 Open AccessUncomputability of phase diagrams
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 oneparameter Hamiltonian for which this is the case.
 Johannes Bausch
 , Toby S. Cubitt
 & James D. Watson

Article
 Open AccessValley interference and spin exchange at the atomic scale in silicon
Coupled donor wavefunctions in silicon are spatially resolved to evidence valley interference processes. An atomicscale 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 AccessFrequencydomain ultrafast passive logic: NOT and XNOR gates
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 AccessDetecting and tracking drift in quantum information processors
Timedependent errors are one of the main obstacles to fullyfledged quantum information processing. Here, the authors develop a general methodology to monitor timedependent errors, which could be used to make other characterisation protocols timeresolved, and demonstrate it on a trappedion qubit.
 Timothy Proctor
 , Melissa Revelle
 & Kevin Young

Article
 Open AccessLearning molecular dynamics with simple language model built upon long shortterm memory neural network
Artificial neural networks have been successfully used for language recognition. Tsai et al. use the same techniques to link between language processing and prediction of molecular trajectories and show capability to predict complex thermodynamics and kinetics arising in chemical or biological physics.
 SunTing Tsai
 , EnJui Kuo
 & Pratyush Tiwary

Article
 Open AccessDemography and the emergence of universal patterns in urban systems
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 AccessConstraints on nonlocality in networks from nosignaling and independence
The nosignaling 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 noinput/binaryoutput triangle network, and show that it admits nontrilocal distributions.
 Nicolas Gisin
 , JeanDaniel Bancal
 & Nicolas Brunner

Article
 Open AccessEfficiency fluctuations and noise induced refrigeratortoheater transition in information engines
Information engines, also known as Maxwell demons, model the interplay between information transfer and work extraction in nonequilibrium systems or even living systems. Here, the authors show that noisy engines are more efficient then perfect ones in extracting work from information.
 Govind Paneru
 , Sandipan Dutta
 & Hyuk Kyu Pak

Article
 Open AccessDecoding quantum errors with subspace expansions
Faulttolerant 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 postprocessing and random measurements in order to mitigate errors in NISQ devices.
 Jarrod R. McClean
 , Zhang Jiang
 & Hartmut Neven

Article
 Open AccessErrormitigated quantum gates exceeding physical fidelities in a trappedion system
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 twoqubit gates’ error rates by two and one order of magnitude respectively.
 Shuaining Zhang
 , Yao Lu
 & Kihwan Kim

Article
 Open AccessA poor man’s coherent Ising machine based on optoelectronic feedback systems for solving optimization problems
Coherent Ising machines are an unconventional optical computing architecture for solving optimization problems. Böhm et al. present a design based on optoelectronic feedback systems that avoids using nonlinear optical materials, improving the prospects for scalability and reliable operation.
 Fabian Böhm
 , Guy Verschaffelt
 & Guy Van der Sande

Article
 Open AccessGlobal labor flow network reveals the hierarchical organization and dynamics of geoindustrial clusters
There is a lack of systematic approaches to identify and analyze the hierarchical structure of geoindustrial 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 geoindustrial clusters exhibit a stronger association between the influx of educatedworkers and financial performance compared to existing aggregation units.
 Jaehyuk Park
 , Ian B. Wood
 & YongYeol Ahn

Article
 Open AccessVariational consistent histories as a hybrid algorithm for quantum foundations
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 AccessReversing the direction of heat flow using quantum correlations
The presence of correlations can strongly affect the evolution of a quantum system. Here, the authors directly observe differences in the dynamics of two spins1/2 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 AccessA space–time tradeoff for implementing a function with master equation dynamics
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 AccessA continuoustime MaxSAT solver with high analog performance
Continuoustime 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 continuoustime solver and simulate its performances in solving MaxSAT and twocolour Ramsey problems.
 Botond Molnár
 , Ferenc Molnár
 & Mária ErcseyRavasz

Article
 Open AccessQuantum machine learning for electronic structure calculations
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 manybody problems.
 Rongxin Xia
 & Sabre Kais

Article
 Open AccessMemory effects can make the transmission capability of a communication channel uncomputable
In information theory one is interested in how much information can be reliably sent over noisy communication channels. Here the authors show that for channels with memory the optimal rate of information transmission is uncomputable.
 David Elkouss
 & David PérezGarcía

Article
 Open AccessStatistical ensembles without typicality
The minimal amount of assumptions to justify the use of maximumentropy 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 AccessInput–output maps are strongly biased towards simple outputs
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 AccessPractical deviceindependent quantum cryptography via entropy accumulation
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 ArnonFriedman
 , Frédéric Dupuis
 & Thomas Vidick

Article
 Open AccessAn equationofstatemeter of quantum chromodynamics transition from deep learning
The large data generated in heavyion collision experiments require careful analysis to understand the physics. Here the authors use the deeplearning method to sort equation of states in QCD transition and analyze the simulated data sets mimicking the heavyion collision experiments.
 LongGang Pang
 , Kai Zhou
 & XinNian Wang

Article
 Open AccessCapacity estimation and verification of quantum channels with arbitrarily correlated errors
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 oneshot quantum capacity in the most general case of arbitrarily correlated errors.
 Corsin Pfister
 , M. Adriaan Rol
 & Stephanie Wehner

Article
 Open AccessGeneralized laws of thermodynamics in the presence of correlations
In presence of intersystem 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 AccessRound complexity in the local transformations of quantum and classical states
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 localityconstrained task of entanglement transformation.
 Eric Chitambar
 & MinHsiu Hsieh

Article
 Open AccessComplete 3Qubit Grover search on a programmable quantum computer
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 AccessMachine learning meets complex networks via coalescent embedding in the hyperbolic space
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 AccessFastforwarding of Hamiltonians and exponentially precise measurements
A complete theory of when and to what extent timeenergy uncertainty relation violations can occur is lacking. Here, the authors set the ground for a rigorous theory to investigate this possibility.
 Yosi Atia
 & Dorit Aharonov

Article
 Open AccessExperimental quantum compressed sensing for a sevenqubit system
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 sevenqubit system.
 C. A. Riofrío
 , D. Gross
 & J. Eisert

Article
 Open AccessQuantum vertex model for reversible classical computing
Solutions of computations can be encoded in the ground state of manybody 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 AccessFundamental limits of repeaterless quantum communications
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 AccessMetamaterial bricks and quantization of metasurfaces
Controlling acoustic fields is of interest for diverse applications. Here the authors develop metasurfaces using a small set of premanufactured threedimensional unit cells, quantized in both the spatial and phase domains, achieving with them acoustic levitation.
 Gianluca Memoli
 , Mihai Caleap
 & Sriram Subramanian

Article
 Open AccessThe backtracking survey propagation algorithm for solving random KSAT problems
The Ksatisfability problem is a combinatorial discrete optimization problem, which for K=3 is NPcomplete, 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 RicciTersenghi

Article
 Open AccessA physical zeroknowledge objectcomparison system for nuclear warhead verification
Zeroknowledge proofs can be used to prove that a statement is true without revealing why it is. Here the authors demonstrate a nonelectronic 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 
Emergence of coherence via transverse condensation in a uniform quasitwodimensional Bose gas
Interacting quantum manybody systems in low dimensions is an active research area in ultracold gases. Here, Chomaz et al.study the dimensional crossover of Bose–Einstein condensation and observe the emergence of phase coherence in an ultracold quasi2D Bose gas confined to a flatbottom trapping potential.
 Lauriane Chomaz
 , Laura Corman
 & Jean Dalibard

Article
 Open AccessMutual information reveals multiple structural relaxation mechanisms in a model glass former
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 
Predicting commuter flows in spatial networks using a radiation model based on temporal ranges
Mathematical tools for understanding network flows with a social component are much less developed than for, say, electric circuits. Ren et al. introduce a method by generalizing the radiation model to flows in spatial networks, which they apply to predict commuter flows in a highway network.
 Yihui Ren
 , Mária ErcseyRavasz
 & Zoltán Toroczkai

Article
 Open AccessMagnon transistor for allmagnon data processing
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 socalled spin waves, known as a magnon, which could be a central element for magneticmaterialbased information processing.
 Andrii V. Chumak
 , Alexander A. Serga
 & Burkard Hillebrands

Review Article 
Ferroelectric tunnel junctions for information storage and processing
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

Article
 Open AccessReconstructing propagation networks with natural diversity and identifying hidden sources
The structure of many complex systems is usually difficult to determine. Zhesi Shen et al. adapt a signalprocessing technique known as compressed sensing to reconstruct the dynamics and structure of a complex propagation network from a small amount of time series data.
 Zhesi Shen
 , WenXu Wang
 & YingCheng Lai