Theoretical physics articles within Nature Communications

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  • Article
    | Open Access

    Most theoretical studies of open quantum systems make several simplifying approximations but experimental devices, and some natural systems, now operate in regimes where those methods break down. Lambert et al. introduce a tractable approach to the spin-boson model without relying on the Born, Markovian and rotating wave approximations.

    • Neill Lambert
    • , Shahnawaz Ahmed
    •  & Franco Nori

  • 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 Unruh effect is a seminal result which illustrates the relative character of the particle concept in QFT, but its validity for extended systems is debated. Here, the authors show how a uniformly accelerated extended system of two coupled spins will evolve to a Gibbs thermal state at the Unruh temperature.

    • Cesar A. Uliana Lima
    • , Frederico Brito
    •  & Daniel A. Turolla Vanzella

  • Article
    | Open Access

    Vibrational interactions are usually considered an obstacle to the creation and manipulation of quantum states; looking at the paradigmatic example of a driven quantum dot, the authors show how they could actually help to engineer optical states that are impossible to reach in the perfectly isolated case.

    • Jake Iles-Smith
    • , Ahsan Nazir
    •  & Dara P. S. McCutcheon

  • Article
    | Open Access

    Strong correlation effects in metals lead to unconventional emergent behavior that depends on the nature of interactions at the microscopic scale. Deng et al. identify distinct signatures of the so-called Mott and Hund regimes, which may guide the theoretical understanding of correlated materials.

    • Xiaoyu Deng
    • , Katharina M. Stadler
    •  & Gabriel Kotliar

  • Article
    | Open Access

    Correlations in quantum thermodynamics are usually regarded as a useful but expensive resource. Here, the authors prove that the work cost of generating multiple copies of a state is lower if the copies are correlated, pointing out at the irreversibility of the process in the single-shot regime.

    • Facundo Sapienza
    • , Federico Cerisola
    •  & Augusto J. Roncaglia

  • Article
    | Open Access

    Typically, a quantum system that dissipates into the environment relaxes to a stationary state. Here the authors identify conditions under which dissipation prevents quantum many-body systems from reaching a steady state and they instead exhibit coherent oscillations.

    • Berislav Buča
    • , Joseph Tindall
    •  & Dieter Jaksch

  • Article
    | Open Access

    Non-stoquastic Hamiltonians are known to be hard to simulate due to the infamous sign problem. Here, the authors study the computational complexity of transforming such Hamiltonians into stoquastic ones and prove that the task is NP-complete even for the simplest class of transformations.

    • Milad Marvian
    • , Daniel A. Lidar
    •  & Itay Hen

  • Article
    | Open Access

    The mathematical structure of quantum measurements and the Born rule are usually imposed as axioms; here, the authors show instead that they are the only possible measurement postulates, if we require that arbitrary partitioning of systems does not change the theory’s predictions.

    • Lluís Masanes
    • , Thomas D. Galley
    •  & Markus P. Müller

  • Article
    | Open Access

    A black hole’s Hawking radiation inevitably deposits records of its location in the environment, making isolation fundamentally impossible. Here, the authors investigate the decoherence of a black hole in a superposition of two positions due to its Hawking radiation and give the rate of this process.

    • Andrew Arrasmith
    • , Andreas Albrecht
    •  & Wojciech H. Zurek

  • Article
    | Open Access

    Reference frames are ultimately physical systems, and thus it should be possible to quantise them in a consistent way. Here, the authors use a relational formalism to quantise a reference frame and show the covariance of physical laws under transformations between such quantum reference frames.

    • Flaminia Giacomini
    • , Esteban Castro-Ruiz
    •  & Časlav Brukner

  • Article
    | Open Access

    Modelling of light-matter interaction in the ultrastrong coupling regime is still debated. Here, the authors study the consequences of gauge freedom for a two-level system in a single-mode cavity, showing that the Jaynes-Cummings model can outperform the quantum Rabi model even for ultrastrong coupling.

    • Adam Stokes
    •  & Ahsan Nazir

  • Article
    | Open Access

    Description of a qubit following an open time-like curve usually incurs into conceptual problems such as violation of entanglement monogamy. Here, the authors show how to use the formalism of pseudo-density operators to describe such a process, showing a proof-of-principle experimental simulation.

    • Chiara Marletto
    • , Vlatko Vedral
    •  & Marco Genovese

  • Article
    | Open Access

    Information Theoretically-secure deterministic programs that self-destruct after a single use are known to be impossible to implement. Here, the authors use quantum states to implement a probabilistic version of this fundamental cryptographic primitive, and provide a proof-of-principle implementation with single photons.

    • Marie-Christine Roehsner
    • , Joshua A. Kettlewell
    •  & Philip Walther

  • Article
    | Open Access

    A general description of observable effects induced by non-Hermitian singularities is complex. Here, Zhong et al. develop such a formalism, showing that loops around the same exceptional point starting from the same point in the same direction do not need to have the same outcome.

    • Qi Zhong
    • , Mercedeh Khajavikhan
    •  & Ramy El-Ganainy

  • Article
    | Open Access

    Ultrafast excitation of materials can cause the formation of hidden phases that are not accessible in thermal equilibrium. Li et al. identify and investigate theoretically a hidden phase that can be accessed in systems with intertwined spin and orbital-ordering such as KCuF3.

    • Jiajun Li
    • , Hugo U. R. Strand
    •  & Martin Eckstein

  • Article
    | Open Access

    Bounding the capacity of thermal attenuators would give a powerful instrument to describe decoherence occurring in optical fibres and free space links. Here, the authors improve on the existing upper bounds in the region of small thermal noise, which is of interest for quantum communication.

    • Matteo Rosati
    • , Andrea Mari
    •  & Vittorio Giovannetti

  • Article
    | Open Access

    Quantum mechanics is expected to provide a consistent description of reality, even when recursively describing systems contained in each other. Here, the authors develop a variant of Wigner’s friend Gedankenexperiment where each of the current interpretations of QM fails in giving a consistent description.

    • Daniela Frauchiger
    •  & Renato Renner

  • Article
    | Open Access

    Understanding the energy cost of entanglement extraction has fundamental implications, in particular for quantum field theory and condensed matter. Here, the authors analyse how the optimal energy cost scales with the number of extracted EPR pairs, when local operations and classical communication are allowed.

    • Cédric Bény
    • , Christopher T. Chubb
    •  & Tobias J. Osborne

  • Article
    | Open Access

    In general the computational requirements for simulating quantum systems scale exponentially but in some cases it is possible to formulate more efficient schemes. Here the authors present an efficient approach to calculate non-Markovian quantum dynamics using matrix product operator methods.

    • A. Strathearn
    • , P. Kirton
    •  & B. W. Lovett

  • Article
    | Open Access

    Samarium hexaboride is a candidate topological insulator but recent experiments have found behaviour indicative of a metallic Fermi liquid phase. Here the authors show that the conflicting observations can be accommodated by a model where strong interactions drive the formation of exotic neutral quasiparticles.

    • Debanjan Chowdhury
    • , Inti Sodemann
    •  & T. Senthil

  • Article
    | Open Access

    The entanglement in a quantum system between a small region and the surrounding environment contains details about the whole state. Nakagawa et al. find a formula for the entanglement entropy of a class of thermal-like states and show that it can be applied more broadly to identify equilibrating states.

    • Yuya O. Nakagawa
    • , Masataka Watanabe
    •  & Sho Sugiura

  • Article
    | Open Access

    Strongly correlated quantum spin liquid phases form when quantum fluctuations prevent magnetic ordering, which normally requires low spin systems that cannot be analyzed semiclassically. Here, the authors show that a large-spin Kitaev model supports a spin liquid phase in the semiclassical limit.

    • Ioannis Rousochatzakis
    • , Yuriy Sizyuk
    •  & Natalia B. Perkins

  • Article
    | Open Access

    Evaluating maximum conversion efficiency from heat to work using non-thermal baths can lead to meaningless results, when based only on the reversibility requirement. Here, the authors solve this problem by identifying the fraction of exchanged energy that necessarily causes a change in entropy.

    • Wolfgang Niedenzu
    • , Victor Mukherjee
    •  & Gershon Kurizki

  • 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

    Diffusive light propagation represents a valuable additional tool for integrated photonic technologies. As an example, here the authors experimentally demonstrate optical equalisation of coherent light propagating in a femtosecond laser written circuit which simulates a dissipatively-coupled quantum chain.

    • Sebabrata Mukherjee
    • , Dmitri Mogilevtsev
    •  & Natalia Korolkova

  • Article
    | Open Access

    Is it possible to single out the thermal state from all the passive states even when not operating in the thermodynamic limit? Here, the authors show that an optimal amount of energy can be extracted from any athermal quantum state when using a machine that operates in a reversible cycle.

    • Carlo Sparaciari
    • , David Jennings
    •  & Jonathan Oppenheim

  • Article
    | Open Access

    In the quest for fault-tolerant quantum computation, being able to interface different topological codes such as surface and color codes would allow to get the best of each code. Here, the authors show how to interface arbitrary topological quantum error correction codes in two dimensions.

    • Hendrik Poulsen Nautrup
    • , Nicolai Friis
    •  & Hans J. Briegel

  • Article
    | Open Access

    Our understanding of open quantum many-body systems is limited because it is difficult to perform a theoretical treatment of both quantum and dissipative effects in large systems. Here the authors present a tensor network method that can find the steady state of 2D driven-dissipative many-body models.

    • Augustine Kshetrimayum
    • , Hendrik Weimer
    •  & Román Orús

  • Article
    | Open Access

    The observation of magnetic excitation continua in putative Kitaev spin liquid compounds is consistent with predictions of exotic quantum behavior, attracting significant interest. Here, the authors show the observed continua could instead be a consequence of realistic non-Kitaev interactions.

    • Stephen M. Winter
    • , Kira Riedl
    •  & Roser Valentí

  • Article
    | Open Access

    Some iridate compounds such as Sr2IrO4 have electronic and atomic structures similar to quasi-2D copper oxides, raising the prospect of high temperature superconductivity. Here, the authors show that there is significant electron-hole asymmetry in iridates, contrary to expectations from the cuprates.

    • Ekaterina M. Pärschke
    • , Krzysztof Wohlfeld
    •  & Jeroen van den Brink

  • Article
    | Open Access

    One of the challenges in studies of quantum many-body physics is finding an efficient way to record the large system wavefunctions. Here the authors present an analysis of the capabilities of recently-proposed neural network representations for storing physically accessible quantum states.

    • Xun Gao
    •  & Lu-Ming Duan

  • Article
    | Open Access

    Coherent control of two-level systems is crucial for achieving fidelity in spectroscopy and quantum computing, but inherent nonlinearities and parameter variation have, to date, required an approximate, numerical approach. Here, Li et al. show how to map a spin ensemble to a spring model so analytic pulses can be designed using linear methods.

    • Jr-Shin Li
    • , Justin Ruths
    •  & Steffen J. Glaser

  • Article
    | Open Access

    The anisotropic Heisenberg model is integrable, possessing a macroscopic number of conserved quantities that constrain the many-body dynamics. Here the authors show numerically that, despite its integrability, it can exhibit diffusive and, at the isotropic point, super-diffusive behaviour.

    • Marko Ljubotina
    • , Marko Žnidarič
    •  & Tomaž Prosen

  • Article
    | Open Access

    Understanding the role of topology in determining electronic structure can lead to the discovery, or appreciation, of materials with exotic properties such as protected surface states. Here, the authors present a framework for identifying topologically distinct band-structures for all 3D space groups.

    • Hoi Chun Po
    • , Ashvin Vishwanath
    •  & Haruki Watanabe

  • Article
    | Open Access

    Integrable models have an infinite number of conserved quantities but most realizations suffer from integrability breaking perturbations. Here the authors show that weakly driving such a system by periodic perturbations leads to large nonlinear responses governed by the approximate conservation laws.

    • Florian Lange
    • , Zala Lenarčič
    •  & Achim Rosch

  • Article
    | Open Access

    Parity-time (PT) symmetry has been mainly studied in optical and weakly interacting open quantum systems without many-body correlations. Here the authors show that in a strongly correlated many-body system the interplay between correlations and PT symmetry leads to the emergence of new critical phenomena.

    • Yuto Ashida
    • , Shunsuke Furukawa
    •  & Masahito Ueda

  • Article
    | Open Access

    Device-independent self-testing is an approach that allows a complete certification of an unknown quantum state, simply by inspecting outcomes of measurements. Here, the authors demonstrate that any pure bipartite entangled state can be self-tested.

    • Andrea Coladangelo
    • , Koon Tong Goh
    •  & Valerio Scarani

  • Article
    | Open Access

    Physicists’ understanding of interacting many-body systems often depends on finding an approximate description in terms of non-interacting particles. Here, the authors propose a systematic approach to identify the closest free particle description of a given model.

    • Christopher J. Turner
    • , Konstantinos Meichanetzidis
    •  & Jiannis K. Pachos

  • Article
    | Open Access

    Quantum metrology investigates the improvement given to precision measurements by exploiting quantum mechanics, but it has been mostly limited to systems with static Hamiltonians. Here the authors study it in the general case of time-varying Hamiltonians, showing that optimizing the quantum Fisher information via quantum control provides an advantage.

    • Shengshi Pang
    •  & Andrew N. Jordan

  • Article
    | Open Access

    High-precision measurements could disclose fundamental dissimilarities between matter and antimatter, which are found imbalanced in the Universe. Here, the authors measure the magnetic moment of the antiproton with six-fold higher accuracy than before, finding it consistent with that of the proton.

    • H. Nagahama
    • , C. Smorra
    •  & S. Ulmer

  • Article
    | Open Access

    Describing thermodynamic processes, fluctuations of work are typically not considered bounded. Here the authors show that in some processes they diverge, making the processes unphysical, and construct a framework to quantify work extraction and work of formation of arbitrary quantum states with bounded fluctuations.

    • Jonathan G. Richens
    •  & Lluis Masanes

  • Article
    | Open Access

    In a future quantum internet, entanglement or a secret key should be efficiently provided between two points via intermediate nodes connected by optical channels. Here the authors derive general rate-loss trade-off for such protocols, that is applicable to any network topology.

    • Koji Azuma
    • , Akihiro Mizutani
    •  & Hoi-Kwong Lo

  • Article
    | Open Access

    Objective collapse theories are formulations of quantum physics that attempt to solve the measurement problem through modified dynamical laws. Here, the authors constrain such theories by testing a generalization of the Leggett-Garg inequality in a superconducting flux qubit experiment.

    • George C. Knee
    • , Kosuke Kakuyanagi
    •  & William J. Munro

  • Article
    | Open Access

    Whether gravity causes decoherence is a natural question on the way of making quantum physics compatible with the theory of gravity. Here the authors devise a general method to estimate gravitational decoherence in any no-signalling physical theory, which holds even if quantum mechanics would be modified.

    • C. Pfister
    • , J. Kaniewski
    •  & S. Wehner

  • Article
    | Open Access

    The discovery that the entropy of black holes is given by their horizon area inspired the holographic principle and led to gauge-gravity duality. Here, the author shows that all Rényi entropies satisfy a similar area law in holographic theories and are given by the areas of dual cosmic branes.

    • Xi Dong

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