Publications

Order by: publication date number of citations

• Quantum spin systems versus Schroedinger operators: A case study in spontaneous symmetry breaking

  Christiaan J. F. van de Ven, Gerrit C. Groenenboom, Robin Reuvers, Nicolaas P. Landsman

  SciPost Phys. 8, 022 (2020) · published 6 February 2020 | Toggle abstract · pdf

  Spontaneous symmetry breaking (SSB) is mathematically tied to some limit, but must physically occur, approximately, before the limit. Approximate SSB has been independently understood for Schroedinger operators with double well potential in the classical limit (Jona-Lasinio et al, 1981; Simon, 1985) and for quantum spin systems in the thermodynamic limit (Anderson, 1952; Tasaki, 2019). We relate these to each other in the context of the Curie-Weiss model, establishing a remarkable relationship between this model (for finite N) and a discretized Schroedinger operator with double well potential.

  8 citations

• Higgs associated production with a vector decaying to two fermions in the geoSMEFT

  Tyler Corbett, Adam Martin

  SciPost Phys. 16, 019 (2024) · published 19 January 2024 | Toggle abstract · pdf

  We present the inclusive calculations of a Higgs boson produced in association with massive vector bosons in the Standard Model Effective Field Theory (SMEFT) to order $1/\Lambda^4$ for the 13 TeV LHC. The calculations include the decay of the vector boson into massless constituents and are done using the geometric formulation of the SMEFT supplemented by the relevant dimension eight operators not included in the geoSMEFT. We include some discussion of distributions to motivate how detailed collider and experimental searches for SMEFT signals could be improved.

  8 citations

• Entanglement entropy with Lifshitz fermions

  Dion Hartmann, Kevin Kavanagh, Stefan Vandoren

  SciPost Phys. 11, 031 (2021) · published 17 August 2021 | Toggle abstract · pdf

  We investigate fermions with Lifshitz scaling symmetry and study their entanglement entropy in 1+1 dimensions as a function of the scaling exponent $z$. Remarkably, in the ground state the entanglement entropy vanishes for even values of $z$, whereas for odd values it is independent of $z$ and equal to the relativistic case with $z=1$. We show this using the correlation method on the lattice, and also using a holographic cMERA approach. The entanglement entropy in a thermal state is a more detailed function of $z$ and $T$ which we plot using the lattice correlation method. The dependence on the even- or oddness of $z$ still shows for small temperatures, but is washed out for large temperatures or large values of $z$.

  8 citations

• Radiation, entanglement and islands from a boundary local quench

  Lorenzo Bianchi, Stefano De Angelis, Marco Meineri

  SciPost Phys. 14, 148 (2023) · published 8 June 2023 | Toggle abstract · pdf

  We study the entanglement and the energy density of the radiation emitted after a local quench in a boundary conformal field theory. We use the operator product expansion (OPE) to predict the early- and late-time behavior of the entanglement entropy and we find, under mild assumptions, a universal form for the leading term, which we test on some treatable two-dimensional examples. We also derive a general upper bound on the entanglement, valid along the full time evolution. In two dimensions, the bound is computed analytically, while in higher dimensions it is evaluated at early and late time via the OPE. These CFT predictions are then compared with a doubly-holographic setup where the CFT is interpreted as a reservoir for the radiation produced on an end-of-the-world brane. After finding the gravitational dual of a boundary local quench, we compute the time evolution of the holographic entanglement entropy, whose late-time behavior is in perfect agreement with the CFT predictions. In the brane+bath picture, unitarity of the time evolution is preserved thanks to the formation of an island. The holographic results can be recovered explicitly from the island formula, in the limit where the tension of the brane is close to the maximal value.

  8 citations

• Exact entanglement in the driven quantum symmetric simple exclusion process

  Denis Bernard, Ludwig Hruza

  SciPost Phys. 15, 175 (2023) · published 20 October 2023 | Toggle abstract · pdf

  Entanglement properties of driven quantum systems can potentially differ from the equilibrium situation due to long range coherences. We confirm this observation by studying a suitable toy model for mesoscopic transport: the open quantum symmetric simple exclusion process (QSSEP). We derive exact formulae for its mutual information between different subsystems in the steady state and show that it satisfies a volume law. Surprisingly, the QSSEP entanglement properties only depend on data related to its transport properties and we suspect that such a relation might hold for more general mesoscopic systems. Exploiting the free probability structure of QSSEP, we obtain these results by developing a new method to determine the eigenvalue spectrum of sub-blocks of random matrices from their so-called local free cumulants - a mathematical result on its own with potential applications in the theory of random matrices. As an illustration of this method, we show how to compute expectation values of observables in systems satisfying the Eigenstate Thermalization Hypothesis (ETH) from the local free cumulants.

  8 citations

• Dynamics of the order parameter statistics in the long range Ising model

  Nishan Ranabhat, Mario Collura

  SciPost Phys. 12, 126 (2022) · published 11 April 2022 | Toggle abstract · pdf

  We study the relaxation of the local ferromagnetic order in the transverse field quantum Ising chain with power-law decaying interactions $1/r^{\alpha}$. We prepare the system in the GHZ state and study the time evolution of the probability distribution function (PDF) of the order parameter within a block of $l$ when quenching the transverse field. The model is known to support long range order at finite temperature for $\alpha \leq 2.0$ . In this regime, quasi-localized topological magnetic defects are expected to strongly affect the equilibration of the full probability distribution. We highlight different dynamical regimes where gaussification mechanism may be slowed down by confinement and eventually breaks. We further study the PDF dynamics induced by changing the effective dimensionality of the system; we mimic this by quenching the range of the interactions. As a matter of fact, the behavior of the system crucially depends on the value of $\alpha$ governing the unitary evolution.

  8 citations

• Fast and automated identification of reactions with low barriers: the decomposition of 3-hydroperoxypropanal

  Mads Koerstz, Maria H. Rasmussen, Jan H. Jensen

  SciPost Chem. 1, 003 (2021) · published 1 October 2021 | Toggle abstract · pdf

  We show how fast semiempirical QM methods can be used to significantly decrease the CPU requirements for automated reaction mechanism discovery, using two different method for generating reaction products: graph-based systematic enumeration of all possible products and the meta-dynamics approach by Grimme (J. Chem. Theory. Comput. 2019, 15, 2847). We test the two approaches on the low-barrier reactions of 3-hydroperoxypropanal, which have been studied by a large variety of reaction discovery approaches and therefore provides a good benchmark. By using PM3 and GFN2-xTB for reaction energy and barrier screening the systematic approach identifies 64 reactions (out of 27,577 possible reactions) for DFT refinement, which in turn identifies the three reactions with lowest barriers plus a previously undiscovered reaction. With optimised hyperparameters meta-dynamics followed by PM3/GFN2-xTB-based screening identifies 15 reactions for DFT refinement, which in turn identifies the three reactions with lowest barrier. The number of DFT refinements can be further reduced to as little as six for both approaches by first verifying the transition states with GFN1-xTB. The main conclusion is that the semiempirical methods are accurate and fast enough to automatically identify promising candidates for DFT refinement for the low barrier reactions of 3-hydroperoxypropanal in about 15-30 minutes using relatively modest computational resources.

  8 citations

• Phase separation in binary Bose mixtures at finite temperature

  Gabriele Spada, Luca Parisi, Gerard Pascual, Nicholas G. Parker, Thomas P. Billam, Sebastiano Pilati, Jordi Boronat, Stefano Giorgini

  SciPost Phys. 15, 171 (2023) · published 18 October 2023 | Toggle abstract · pdf

  We investigate the magnetic behavior of finite-temperature repulsive two-component Bose mixtures by means of exact path-integral Monte-Carlo simulations. Novel algorithms are implemented for the free energy and the chemical potential of the two components. Results on the magnetic susceptibility suggest that the conditions for phase separation are not modified from the zero temperature case. This contradicts previous predictions based on approximate theories. We also determine the temperature dependence of the chemical potential and the contact parameters for experimentally relevant balanced mixtures.

  8 citations

• Performance versus resilience in modern quark-gluon tagging

  Anja Butter, Barry M. Dillon, Tilman Plehn, Lorenz Vogel

  SciPost Phys. Core 6, 085 (2023) · published 12 December 2023 | Toggle abstract · pdf

  Discriminating quark-like from gluon-like jets is, in many ways, a key challenge for many LHC analyses. First, we use a known difference in PYTHIA and HERWIG simulations to show how decorrelated taggers would break down when the most distinctive feature is aligned with theory uncertainties. We propose conditional training on interpolated samples, combined with a controlled Bayesian network, as a more resilient framework. The interpolation parameter can be used to optimize the training evaluated on a calibration dataset, and to test the stability of this optimization. The interpolated training might also be useful to track generalization errors when training networks on simulations.

  8 citations

• Many-body Bell inequalities for bosonic qubits

  Jan Chwedenczuk

  SciPost Phys. Core 5, 025 (2022) · published 29 April 2022 | Toggle abstract · pdf

  Since John Bell formulated his paramount inequality for a pair of spin-$1/2$ particles, quantum mechanics has been confronted with the postulates of local realism with various equivalent configurations. Current technology, with its advanced manipulation and detection methods, allows to extend the Bell tests to more complex structures. The aim of this work is to analyze a set of Bell inequalities suitable for a possibly broad family of many-body systems with the focus on bosonic qubits. We develop a method that allows for a step-by-step study of the many-body Bell correlations, for instance among atoms forming a two-mode Bose-Einstein condensate or between photons obtained from the parametric-down conversion. The presented approach is valid both for cases of fixed and non-fixed number of particles, hence it allows for a thorough analysis of quantum correlations in a variety of many-body systems.

  8 citations