Publications

Order by: publication date number of citations

• Asymmetric transport in long-range interacting chiral spin chains

  Javad Vahedi

  SciPost Phys. Core 5, 021 (2022) · published 13 April 2022 | Toggle abstract · pdf

  Harnessing power-law interactions ($1/r^\alpha$) in a large variety of physical systems are increasing. We study the dynamics of chiral spin chains as a possible multi-directional quantum channel. This arises from the nonlinear character of the dispersion with complex quantum interference effects. Using complementary numerical and analytical techniques, we propose a model to guide quantum states to a desired direction. We illustrate our approach using the long-range XXZ model modulated by Dzyaloshinskii-Moriya (DM) interaction. By exploring non-equilibrium dynamics after a local quantum quench, we identify the interplay of interaction range $\alpha$ and Dzyaloshinskii-Moriya coupling giving rise to an appreciable asymmetric spin excitations transport. This could be interesting for quantum information protocols to transfer quantum states, and it may be testable with current trapped-ion experiments. We further explore the growth of block entanglement entropy in these systems, and an order of magnitude reduction is distinguished.

  1 citation

• xSPDE3: Extensible software for stochastic ordinary and partial differential equations

  Simon Kiesewetter, Ria R. Joseph, Peter D. Drummond

  SciPost Phys. Codebases 17 (2023) · published 2 October 2023 | Toggle abstract · pdf

  The xSPDE toolbox treats stochastic partial and ordinary differential equations, with applications in biology, chemistry, engineering, medicine, physics and quantum technologies. It computes statistical averages, including time-step and/or sampling error estimation. xSPDE can provide higher order convergence, Fourier spectra and probability densities. The toolbox has graphical output and $\chi^{2}$ statistics, as well as weighted, projected, or forward-backward equations. It can generate input-output quantum spectra. All equations may have independent periodic, Dirichlet, and Neumann or Robin boundary conditions in any dimension, for any vector field component, and at either end of any interval.

  1 citation

• Codebase release 3.44 for xSPDE

  Simon Kiesewetter, Ria R. Joseph, Peter D. Drummond

  SciPost Phys. Codebases 17-r3.44 (2023) · published 2 October 2023 | Toggle abstract · src

  The xSPDE toolbox treats stochastic partial and ordinary differential equations, with applications in biology, chemistry, engineering, medicine, physics and quantum technologies. It computes statistical averages, including time-step and/or sampling error estimation. xSPDE can provide higher order convergence, Fourier spectra and probability densities. The toolbox has graphical output and $\chi^{2}$ statistics, as well as weighted, projected, or forward-backward equations. It can generate input-output quantum spectra. All equations may have independent periodic, Dirichlet, and Neumann or Robin boundary conditions in any dimension, for any vector field component, and at either end of any interval.

  1 citation

• Floquet fractional Chern insulators and competing phases in twisted bilayer graphene

  Peng-Sheng Hu, Yi-Han Zhou, Zhao Liu

  SciPost Phys. 15, 148 (2023) · published 10 October 2023 | Toggle abstract · pdf

  We study the many-body physics in twisted bilayer graphene coupled to periodic driving of a circularly polarized light when electron-electron interactions are taken into account. In the limit of high driving frequency $\Omega$, we use Floquet theory to formulate the system by an effective static Hamiltonian truncated to the order of $\Omega^{-2}$, which consists of a single-electron part and the screened Coulomb interaction. We numerically simulate this effective Hamiltonian by extensive exact diagonalization in the parameter space spanned by the twist angle and the driving strength. Remarkably, in a wide region of the parameter space, we identify Floquet fractional Chern insulator states in the partially filled Floquet valence bands. We characterize these topologically ordered states by ground-state degeneracy, spectral flow, and entanglement spectrum. In regions of the parameter space where fractional Chern insulator states are absent, we find topologically trivial charge density waves and band-dispersion-induced Fermi liquids which strongly compete with fractional Chern insulator states.

  1 citation

• Monte Carlo matrix-product-state approach to the false vacuum decay in the monitored quantum Ising chain

  Jeffrey Allan Maki, Anna Berti, Iacopo Carusotto, Alberto Biella

  SciPost Phys. 15, 152 (2023) · published 11 October 2023 | Toggle abstract · pdf

  In this work we characterize the false vacuum decay in the ferromagnetic quantum Ising chain with a weak longitudinal field subject to continuous monitoring of the local magnetization. Initializing the system in a metastable state, the false vacuum, we study the competition between coherent dynamics, which tends to create resonant bubbles of the true vacuum, and measurements which induce heating and reduce the amount of quantum correlations. To this end we exploit a numerical approach based on the combination of matrix product states with stochastic quantum trajectories which allows for the simulation of the trajectory-resolved non-equilibrium dynamics of interacting many-body systems in the presence of continuous measurements. We show how the presence of measurements affects the false vacuum decay: At short times the departure from the local minimum is accelerated while at long times the system thermalizes to an infinite-temperature incoherent mixture. For large measurement rates the system enters a quantum Zeno regime. The false vacuum decay and the thermalization physics are characterized in terms of the magnetization, connected correlation function, and the trajectory-resolved entanglement entropy.

  1 citation

• A time-dependent momentum-resolved scattering approach to core-level spectroscopies

  Krissia Zawadzki, Alberto Nocera, Adrian E. Feiguin

  SciPost Phys. 15, 166 (2023) · published 17 October 2023 | Toggle abstract · pdf

  While new light sources allow for unprecedented resolution in experiments with X-rays, a theoretical understanding of the scattering cross-section is lacking. In the particular case of strongly correlated electron systems, numerical techniques are quite limited, since conventional approaches rely on calculating a response function (Kramers-Heisenberg formula) that is obtained from a perturbative analysis of scattering processes in the frequency domain. This requires a knowledge of a full set of eigenstates in order to account for all intermediate processes away from equilibrium, limiting the applicability to small tractable systems. In this work, we present an alternative paradigm, recasting the problem in the time domain and explicitly solving the time-dependent Schrödinger equation without the limitations of perturbation theory: a faithful simulation of the scattering processes taking place in actual experiments, including photons and core electrons. We show how this approach can yield the full time and momentum resolved Resonant Inelastic X-Ray Scattering (RIXS) spectrum of strongly interacting many-body systems. We demonstrate the formalism with an application to Mott insulating Hubbard chains using the time-dependent density matrix renormalization group method, which does not require a priory knowledge of the eigenstates and can solve very large systems with dozens of orbitals. This approach can readily be applied to systems out of equilibrium without modification and generalized to other spectroscopies.

  1 citation

• Resolving phase transitions with discontinuous Galerkin methods

  Eduardo Grossi, Nicolas Wink

  SciPost Phys. Core 6, 071 (2023) · published 25 October 2023 | Toggle abstract · pdf

  We demonstrate the applicability and advantages of Discontinuous Galerkin (DG) schemes in the context of the Functional Renormalization Group (fRG). We investigate the $O(N)$-model in the large $N$ limit. It is shown that the flow equation for the effective potential can be cast into a conservative form. We discuss results for the Riemann problem, as well as initial conditions leading to a first and second order phase transition. In particular, we unravel the mechanism underlying first order phase transitions, based on the formation of a shock in the derivative of the effective potential.

  1 citation

• Interference dynamics of matter-waves of SU($N$) fermions

  Wayne Jordan Chetcuti, Andreas Osterloh, Luigi Amico, Juan Polo

  SciPost Phys. 15, 181 (2023) · published 30 October 2023 | Toggle abstract · pdf

  Interacting N-component fermions spatially confined in ring-shaped potentials display specific coherence properties. The orbital angular momentum per particle of such systems can be quantized to fractional values specifically depending on the particle-particle interaction. Here we demonstrate how to monitor the state of the system through homodyne (momentum distribution) and self-heterodyne system's expansion. For homodyne protocols, the momentum distribution is affected by the particle statistics in two distinctive ways. The first effect is a purely statistical one: at zero interactions, the characteristic hole in the momentum distribution around the momentum k=0 opens up once half of the SU(N) Fermi sphere is displaced. The second effect originates from the interaction: The fractionalization in the interacting system manifests itself by an additional "delay" in the flux for the occurrence of the hole, that now becomes a characteristic minimum at k=0. We demonstrate that the angular momentum fractional quantization is reflected in the self-heterodyne interference as specific dislocations in interferograms. Our analysis demonstrates how the study of the interference fringes grants us access to both number of particles and number of components of SU(N) fermions.

  1 citation

• Codebase release 1.0 for Nevanlinna.jl

  Kosuke Nogaki, Jiani Fei, Emanuel Gull, Hiroshi Shinaoka

  SciPost Phys. Codebases 19-r1.0 (2023) · published 13 November 2023 | Toggle abstract · src

  We introduce a Julia implementation of the recently proposed Nevanlinna analytic continuation method. The method is based on Nevanlinna interpolants and inherently preserves the causality of a response function due to its construction. For theoretical calculations without statistical noise, this continuation method is a powerful tool to extract real-frequency information from numerical input data on the Matsubara axis. This method has been applied to first-principles calculations of correlated materials. This paper presents its efficient and full-featured open-source implementation of the method including the Hamburger moment problem and smoothing.

  1 citation

• Exploring the vortex phase diagram of Bogoliubov-de Gennes disordered superconductors

  Bo Fan (范波), Antonio Miguel Garcia Garcia

  SciPost Phys. 15, 196 (2023) · published 15 November 2023 | Toggle abstract · pdf

  We study the interplay of vortices and disorder in a two-dimensional disordered superconductor at zero temperature described by the Bogoliubov-de Gennes (BdG) self-consistent formalism for lattices of sizes up to 100×100 where the magnetic flux is introduced by the Peierls substitution. We model substantially larger lattice size than in previous approaches (≤36×36) which has allowed us to identify a rich phase diagram as a function of the magnetic flux and the disorder strength. For sufficiently weak disorder, and not too strong magnetic flux, we observe a slightly distorted Abrikosov triangular vortex lattice. An increase in the magnetic flux leads to an unexpected rectangular vortex lattice. A further increase in disorder, or flux, gradually destroys the lattice symmetry though strong vortex repulsion persists. An even stronger disorder leads to deformed single vortices with an inhomogeneous core. As the number of vortices increases, vortex overlap becomes more frequent. Finally, we show that global phase coherence is a feature of all these phases and that disorder enhances substantially the critical magnetic flux with respect to the clean limit with a maximum on the metallic side of the insulating transition.

  1 citation