Publications

Order by: publication date number of citations

• On the quantum simulation of complex networks

  Duarte Magano, João Moutinho, Bruno Coutinho

  SciPost Phys. Core 6, 058 (2023) · published 24 August 2023 | Toggle abstract · pdf

  Quantum walks provide a natural framework to approach graph problems with quantum computers, exhibiting speedups over their classical counterparts for tasks such as the search for marked nodes or the prediction of missing links. Continuous-time quantum walk algorithms assume that we can simulate the dynamics of quantum systems where the Hamiltonian is given by the adjacency matrix of the graph. It is known that such can be simulated efficiently if the underlying graph is row-sparse and efficiently row-computable. While this is sufficient for many applications, it limits the applicability for this class of algorithms to study real world complex networks, which, among other properties, are characterized by the existence of a few densely connected nodes, called hubs. In other words, complex networks are typically not row-sparse, even though the average connectivity over all nodes can be very small. In this work, we extend the state-of-the-art results on quantum simulation to graphs that contain a small number of hubs, but that are otherwise sparse. Hopefully, our results may lead to new applications of quantum computing to network science.

  2 citations

• Engaging with the State. Illegalized migrants, welfare institutions and the law in French-Speaking Belgium

  Sophie Andreetta

  Mig. Pol. 1, 001 (2022) · published 21 March 2022 | Toggle abstract · pdf

  By highlighting informal strategies and solidarities on the one hand, and protests on the other, current studies of citizenship and illegalized migration describe two main forms of political subjectivities among illegalized migrants: ‘without’ the state or ‘against’ it. In contrast, this article unpacks how migrants make use of state laws and institutions, voice expectations, and pursue their claims using official venues – in short, how they act ‘with’ the state. It builds on ethnographic fieldwork on illegalized migrants’ welfare requests in French-speaking Belgium and the various sets of actors involved in assessing or furthering their cases. Migrants’ discourses and expectations of the welfare office provide insights into their understandings of the state, highlight the crucial role of immigration lawyers in brokering cases, and ultimately allow for a more nuanced reading of the idea that welfare dependency leads to deportability. On a theoretical level, this article contributes to ongoing debates both in the study of statehood and in migration studies, showing how procedural fairness can be a central aspect of – in this case – migrants’ relationship to and expectations of the state, and how migrants’ strategies and practices of inclusion can also be formal ones, based on existing state laws and institutions.

  2 citations

• Probing chaos in the spherical p-spin glass model

  Lorenzo Correale, Anatoli Polkovnikov, Marco Schirò, Alessandro Silva

  SciPost Phys. 15, 190 (2023) · published 13 November 2023 | Toggle abstract · pdf

  We study the dynamics of a quantum $p$-spin glass model starting from initial states defined in microcanonical shells, in a classical regime. We compute different chaos estimators, such as the Lyapunov exponent and the Kolmogorov-Sinai entropy, and find a marked maximum as a function of the energy of the initial state. By studying the relaxation dynamics and the properties of the energy landscape we show that the maximal chaos emerges in correspondence with the fastest spin relaxation and the maximum complexity, thus suggesting a qualitative picture where chaos emerges as the trajectories are scattered over the exponentially many saddles of the underlying landscape. We also observe hints of ergodicity breaking at low energies, indicated by the correlation function and a maximum of the fidelity susceptibility.

  2 citations

• The eikonal model of reactions involving exotic nuclei; Roy Glauber's legacy in today's nuclear physics

  Pierre Capel

  SciPost Phys. Proc. 3, 017 (2020) · published 25 February 2020 | Toggle abstract · pdf

  In this contribution, the eikonal approximation developed by Roy Glauber to describe high-energy quantum collisions is presented. This approximation has been-and still is-extensively used to analyse reaction measurements performed to study the structure of nuclei far from stability. This presentation focuses more particularly on the application of the eikonal approximation to the study of halo nuclei in modern nuclear physics. To emphasise Roy Glauber's legacy in today's nuclear physics, recent extensions of this model are reviewed.

  2 citations

• Learning Summary Statistics for Bayesian Inference with Autoencoders

  Carlo Albert, Simone Ulzega, Firat Ozdemir, Fernando Perez-Cruz, Antonietta Mira

  SciPost Phys. Core 5, 043 (2022) · published 1 September 2022 | Toggle abstract · pdf

  For stochastic models with intractable likelihood functions, approximate Bayesian computation offers a way of approximating the true posterior through repeated comparisons of observations with simulated model outputs in terms of a small set of summary statistics. These statistics need to retain the information that is relevant for constraining the parameters but cancel out the noise. They can thus be seen as thermodynamic state variables, for general stochastic models. For many scientific applications, we need strictly more summary statistics than model parameters to reach a satisfactory approximation of the posterior. Therefore, we propose to use the inner dimension of deep neural network based Autoencoders as summary statistics. To create an incentive for the encoder to encode all the parameter-related information but not the noise, we give the decoder access to explicit or implicit information on the noise that has been used to generate the training data. We validate the approach empirically on two types of stochastic models.

  2 citations

• Massive particle interferometry with lattice solitons

  Piero Naldesi, Juan Polo, Peter D. Drummond, Vanja Dunjko, Luigi Amico, Anna Minguzzi, Maxim Olshanii

  SciPost Phys. 15, 187 (2023) · published 8 November 2023 | Toggle abstract · pdf

  We discuss an interferometric scheme employing interference of bright solitons formed as specific bound states of attracting bosons on a lattice. We revisit the proposal of Castin and Weiss [Phys. Rev. Lett. vol. 102, 010403 (2009)] for using the scattering of a quantum matter-wave soliton on a barrier in order to create a coherent superposition state of the soliton being entirely to the left of the barrier and being entirely to the right of the barrier. In that proposal, it was assumed that the scattering is perfectly elastic, i.e. that the center-of-mass kinetic energy of the soliton is lower than the chemical potential of the soliton. Here we relax this assumption: By employing a combination of Bethe ansatz and DMRG-based analysis of the dynamics of the appropriate many-body system, we find that the interferometric fringes persist even when the center-of-mass kinetic energy of the soliton is above the energy needed for its complete dissociation into constituent atoms.

  2 citations

• Decoding stringy near-supersymmetric black holes

  Chi-Ming Chang, Li Feng, Ying-Hsuan Lin, Yi-Xiao Tao

  SciPost Phys. 16, 109 (2024) · published 23 April 2024 | Toggle abstract · pdf

  Building on the recent discovery of the first candidate black hole operator in the $\mathcal{N}=4$ super-Yang-Mills, we explore the near-supersymmetric aspects of the theory that capture lightly excited, highly stringy black holes. We extend the superspace formalism describing the classically supersymmetric (1/16-BPS) sector of $\mathcal{N}=4$ super-Yang-Mills and compute a large number of one-loop anomalous dimensions. Despite being in the highly stringy regime, we find hints of a gap in the spectrum, similar to that found by a gravitational path integral. We also determine the actual expression of the first candidate black hole operator at weak gauge coupling, going beyond the cohomological construction.

  2 citations

• Circuit Complexity through phase transitions: Consequences in quantum state preparation

  Sebastián Roca-Jerat, Teresa Sancho-Lorente, Juan Román-Roche, David Zueco

  SciPost Phys. 15, 186 (2023) · published 8 November 2023 | Toggle abstract · pdf

  In this paper, we analyze the circuit complexity for preparing ground states of quantum many-body systems. In particular, how this complexity grows as the ground state approaches a quantum phase transition. We discuss different definitions of complexity, namely the one following the Fubini-Study metric or the Nielsen complexity. We also explore different models: Ising, ZZXZ or Dicke. In addition, different forms of state preparation are investigated: analytic or exact diagonalization techniques, adiabatic algorithms (with and without shortcuts), and Quantum Variational Eigensolvers. We find that the divergence (or lack thereof) of the complexity near a phase transition depends on the non-local character of the operations used to reach the ground state. For Fubini-Study based complexity, we extract the universal properties and their critical exponents. In practical algorithms, we find that the complexity depends crucially on whether or not the system passes close to a quantum critical point when preparing the state. For both VQE and Adiabatic algorithms, we provide explicit expressions and bound the growth of complexity with respect to the system size and the execution time, respectively.

  2 citations

• Twist-3 partonic distributions from lattice QCD

  Shohini Bhattacharya, Krzysztof Cichy, Martha Constantinou, Andreas Metz, Aurora Scapellato, Fernanda Steffens

  SciPost Phys. Proc. 8, 057 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Twist-3 partonic distributions contain important information that characterizes nucleon's structure. In this work, we show our lattice exploration of the twist-3 PDFs $g_T(x)$, and $h_L(x)$. We also present our preliminary results on the twist-3 GPD $\tilde{G}_2(x)$. We use the quasi-distribution approach to connect the lattice-extracted matrix elements, renormalized in the RI/MOM scheme, to light-cone distributions, applying the matching procedure that we developed in parallel. We also calculate the twist-2 counterparts of $g_T(x)$ and $h_L(x)$, i.e. $g_1(x)$, and $h_1(x)$, and test the Wandzura-Wilczek approximation.

  2 citations

• Knots and entanglement

  Jin-Long Huang, John McGreevy, Bowen Shi

  SciPost Phys. 14, 141 (2023) · published 2 June 2023 | Toggle abstract · pdf

  We extend the entanglement bootstrap program to (3+1)-dimensions. We study knotted excitations of (3+1)-dimensional liquid topological orders and exotic fusion processes of loops. As in previous work in (2+1)-dimensions [Ann. Phys. 418, 168164 (2020), Phys. Rev. B 103, 115150 (2021)], we define a variety of superselection sectors and fusion spaces from two axioms on the ground state entanglement entropy. In particular, we identify fusion spaces associated with knots. We generalize the information convex set to a new class of regions called immersed regions, promoting various theorems to this new context. Examples from solvable models are provided; for instance, a concrete calculation of knot multiplicity shows that the knot complement of a trefoil knot can store quantum information. We define spiral maps that allow us to understand consistency relations for torus knots as well as spiral fusions of fluxes.

  2 citations