Publications

Order by: publication date number of citations

• Ultra-high energy neutrinos searches with the Pierre Auger Observatory

  Marta Trini for the Pierre Auger Collaboration

  SciPost Phys. Proc. 1, 047 (2019) · published 22 February 2019 | Toggle abstract · pdf

  In the EeV range, neutrinos are expected to be produced by ultra-high energy cosmic rays interactions with the Cosmic Microwave Background during propagation in the Universe. We report on the search for ultra-high energy neutrinos in data collected with the Surface Detector of the Pierre Auger Observatory. The searches are most efficient in the zenith angle range from 60 degrees to 95 degrees with tau neutrinos skimming in the Earth playingdominant role. The present non-detection of UHE neutrinos in the Pierre Auger Observatory excludes the most optimistic scenarios of neutrino production in terms of UHE cosmic rays chemical composition and cosmological evolution of the acceleration sites. We also report on the searches for neutrinos in coincidence with the recent Gravitational Wave events detected by LIGO/Virgo.

• Ergodic Archimedean dimers

  Henrik Schou Røising, Zhao Zhang

  SciPost Phys. Core 6, 054 (2023) · published 11 August 2023 | Toggle abstract · pdf

  We study perfect matchings, or close-packed dimer coverings, of finite sections of the eleven Archimedean lattices and give a constructive proof showing that any two perfect matchings can be transformed into each other using small sets of local ring-exchange moves. This result has direct consequences for formulating quantum dimer models with a resonating valence bond ground state, i.e., a superposition of all dimer coverings compatible with the boundary conditions. On five of the composite Archimedean lattices we supplement the sufficiency proof with translationally invariant reference configurations that prove the strict necessity of the sufficient terms with respect to ergodicity. We provide examples of and discuss frustration-free deformations of the quantum dimer models on two tripartite lattices.

• Experimental input from $e^+e^-$ machines to hadronic contribution to muon (g-2)

  M. N. Achasov, R. R. Akhmetshin, A. N. Amirkhanov, A. V. Anisenkov, V. M. Aulchenko, V. Sh. Banzarov, A. Yu. Barnyakov, N. S. Bashtovoy, K. I. Beloborodov, A. V. Berdyugin, D. E. Berkaev, A. G. Bogdanchikov, A. E. Bondar, A. A. Botov, A. V. Bragin, T. V. Dimova, V. P. Druzhinin, S. I. Eidelman, D. A. Epifanov, L. B. Epshteyn, A. L. Erofeev, G. V. Fedotovich, S. E. Gayazov, V. B. Golubev, A. A. Grebenuk, S. S. Gribanov, D. N. Grigoriev, F. V. Ignatov, V. L. Ivanov, L. V. Kardapoltsev, S. V. Karpov, V. F. Kazanin, A. G. Kharlamov, A. N. Kirpotin, I. A. Koop, A. A. Korol, A. A. Korobov, S. V. Koshuba, A. N. Kozyrev, E. A. Kozyrev, D. P. Kovrizhin, P. P. Krokovny, A. S. Kupich, A. E. Kuzmenko, A. S. Kuzmin, R. A. Litvinov, I. B. Logashenko, P. A. Lukin, K. A. Martin, N. A. Melnikova, K. Yu. Mikhailov, A. E. Obrazovsky, V. S. Okhapkin, A. V. Otboev, E. V. Pakhtusova, Yu. N. Pestov, A. S. Popov, K. V. Pugachev, G. P. Razuvaev, A. A. Ruban, N. M. Ryskulov, A. E. Ryzhenenkov, A. I. Senchenko, S. I. Serednyakov, Yu. M. Shatunov, P. Yu. Shatunov, V. E. Shebalin, D. N. Shemyakin, D. A. Shtol, B. A. Shwartz, D. B. Shwartz, A. L. Sibidanov, Z. K. Silagadze, E. P. Solodov, I. K. Surin, A. A. Talyshev, V. M. Titov, S. S. Tolmachev, A. I. Vorobiov, I. M. Zemlyansky, Yu. V. Yudin

  SciPost Phys. Proc. 1, 034 (2019) · published 21 February 2019 | Toggle abstract · pdf

  Precise study of the hadrons production in $e^+e^-$ annihilation at low energies provides important information about interactions of light quarks and spectroscopy of their bound states. These studies are especially important for theoretical calculations of the muon $(g-2)$ via the Standard Model because of the present difference between theoretical and experimental values exceeds three standard deviations. In this report we will discuss current status and recent results obtained by the CMD-3 experiment and will give a brief look to status of the BaBar and Belle II experiments.

• Quantum-inspired tempering for ground state approximation using artificial neural networks

  Tameem Albash, Conor Smith, Quinn Campbell, Andrew D. Baczewski

  SciPost Phys. 14, 121 (2023) · published 19 May 2023 | Toggle abstract · pdf

  A large body of work has demonstrated that parameterized artificial neural networks (ANNs) can efficiently describe ground states of numerous interesting quantum many-body Hamiltonians. However, the standard variational algorithms used to update or train the ANN parameters can get trapped in local minima, especially for frustrated systems and even if the representation is sufficiently expressive. We propose a parallel tempering method that facilitates escape from such local minima. This methods involves training multiple ANNs independently, with each simulation governed by a Hamiltonian with a different "driver" strength, in analogy to quantum parallel tempering, and it incorporates an update step into the training that allows for the exchange of neighboring ANN configurations. We study instances from two classes of Hamiltonians to demonstrate the utility of our approach using Restricted Boltzmann Machines as our parameterized ANN. The first instance is based on a permutation-invariant Hamiltonian whose landscape stymies the standard training algorithm by drawing it increasingly to a false local minimum. The second instance is four hydrogen atoms arranged in a rectangle, which is an instance of the second quantized electronic structure Hamiltonian discretized using Gaussian basis functions. We study this problem in a minimal basis set, which exhibits false minima that can trap the standard variational algorithm despite the problem's small size. We show that augmenting the training with quantum parallel tempering becomes useful to finding good approximations to the ground states of these problem instances.

• Quantum-critical properties of the one- and two-dimensional random transverse-field Ising model from large-scale quantum Monte Carlo simulations

  Calvin Krämer, Jan Alexander Koziol, Anja Langheld, Max Hörmann, Kai Phillip Schmidt

  SciPost Phys. 17, 061 (2024) · published 23 August 2024 | Toggle abstract · pdf

  We study the ferromagnetic transverse-field Ising model with quenched disorder at $T = 0$ in one and two dimensions by means of stochastic series expansion quantum Monte Carlo simulations using a rigorous zero-temperature scheme. Using a sample-replication method and averaged Binder ratios, we determine the critical shift and width exponents $\nu_\mathrm{s}$ and $\nu_\mathrm{w}$ as well as unbiased critical points by finite-size scaling. Further, scaling of the disorder-averaged magnetisation at the critical point is used to determine the order-parameter critical exponent $\beta$ and the critical exponent $\nu_{\mathrm{av}}$ of the average correlation length. The dynamic scaling in the Griffiths phase is investigated by measuring the local susceptibility in the disordered phase and the dynamic exponent $z'$ is extracted. By applying various finite-size scaling protocols, we provide an extensive and comprehensive comparison between the different approaches on equal footing. The emphasis on effective zero-temperature simulations resolves several inconsistencies in existing literature.

• Stochastic representation of the quantum quartic oscillator

  Gennaro Tucci, Stefano De Nicola, Sascha Wald, Andrea Gambassi

  SciPost Phys. Core 6, 029 (2023) · published 14 April 2023 | Toggle abstract · pdf

  Recent experimental advances have inspired the development of theoretical tools to describe the non-equilibrium dynamics of quantum systems. Among them an exact representation of quantum spin systems in terms of classical stochastic processes has been proposed. Here we provide first steps towards the extension of this stochastic approach to bosonic systems by considering the one-dimensional quantum quartic oscillator. We show how to exactly parameterize the time evolution of this prototypical model via the dynamics of a set of classical variables. We interpret these variables as stochastic processes, which allows us to propose a novel way to numerically simulate the time evolution of the system. We benchmark our findings by considering analytically solvable limits and providing alternative derivations of known results.

• Strengthening the atom-field coupling through the deep-strong regime via pseudo-Hermitian Hamiltonians

  M. A. de Ponte, F. Oliveira Neto, P. M. Soares, M. H. Y. Moussa

  SciPost Phys. 15, 091 (2023) · published 13 September 2023 | Toggle abstract · pdf

  We present a strategy for strengthening the atom-field interaction through a pseudo-Hermitian Jaynes-Cummings Hamiltonian. Apart from the engineering of an effective non-Hermitian Hamiltonian, our strategy also relies on the accomplishment of short-time measurements on canonically conjugate variables. The resulting fast Rabi oscillations may be used for many quantum optics purposes and specially to shorten the processing time of quantum information.

• The resistance of quantum entanglement to temperature in the Kugel-Khomskii model

  Valerii E. Valiulin, Andrey V. Mikheyenkov, Nikolay M. Chtchelkatchev, Kliment I. Kugel

  SciPost Phys. Core 6, 025 (2023) · published 4 April 2023 | Toggle abstract · pdf

  The Kugel-Khomskii model with entangled spin and orbital degrees of freedom is a good testing ground for many important features in quantum information processing, such as robust gaps in the entanglement spectra. Here, we demonstrate that the entanglement can be also robust under effect of temperature within a wide range of parameters. It is shown, in particular, that the temperature dependence of entanglement often exhibits a nonmonotonic behavior. Namely, there turn out to be ranges of the model parameters, where entanglement is absent at zero temperature, but then, with an increase in temperature, it appears, passes through a maximum, and again vanishes.

• Dissipative preparation of a Floquet topological insulator in an optical lattice via bath engineering

  Alexander Schnell, Christof Weitenberg, André Eckardt

  SciPost Phys. 17, 052 (2024) · published 14 August 2024 | Toggle abstract · pdf

  Floquet engineering is an important tool for realizing topologically nontrivial band structures for charge-neutral atoms in optical lattices. However, the preparation of a topological-band-insulator-type state of fermions, with one nontrivial quasi-energy band filled completely and the others empty, is challenging as a result of both driving induced heating as well as imperfect adiabatic state preparation (with the latter induced by the unavoidable gap closing when passing the topological transition). An alternative procedure that has been proposed is to prepare such states dissipatively, i.e. as a steady state that emerges when coupling the system to reservoirs. Here we discuss a concrete scheme that couples the system to a weakly interacting Bose condensate given by second atomic species acting as a heat bath. Our strategy relies on the engineering of the potential for the bath particles, so that they occupy weakly coupled tubes perpendicular to the two-dimensional system. Using Floquet-Born-Markov theory, we show that the resulting nonequilibrium steady state of the driven-dissipative system approximates a topological insulator. We even find indications for the approximate stabilization of an anomalous Floquet topological insulator, a state that is impossible to realize in equilibrium.

• Krylov complexity in a natural basis for the Schrödinger algebra

  Dimitrios Patramanis, Watse Sybesma

  SciPost Phys. Core 7, 037 (2024) · published 20 June 2024 | Toggle abstract · pdf

  We investigate operator growth in quantum systems with two-dimensional Schrödinger group symmetry by studying the Krylov complexity. While feasible for semisimple Lie algebras, cases such as the Schrödinger algebra which is characterized by a semi-direct sum structure are complicated. We propose to compute Krylov complexity for this algebra in a natural orthonormal basis, which produces a pentadiagonal structure of the time evolution operator, contrasting the usual tridiagonal Lanczos algorithm outcome. The resulting complexity behaves as expected. We advocate that this approach can provide insights to other non-semisimple algebras.