Publications

Order by: publication date number of citations

• Mapping a dissipative quantum spin chain onto a generalized Coulomb gas

  Oscar Bouverot-Dupuis

  SciPost Phys. 17, 130 (2024) · published 11 November 2024 | Toggle abstract · pdf

  An XXZ spin chain at zero magnetization is subject to spatially correlated baths acting as dissipation. We show that the low-energy excitations of this model are described by a dissipative sine-Gordon field theory, i.e. a sine-Gordon action with an additional long-range interaction emerging from dissipation. The field theory is then exactly mapped onto a generalized Coulomb gas which, in addition to the usual integer charges, displays half-integer charges that originate from the dissipative baths. These new charges come in pairs linked by a charge independent logarithmic interaction. In the Coulomb gas picture, we identify a Berezinsky–Kosterlitz–Thouless-like phase transition corresponding to the binding of charges and derive the associated perturbative renormalization group equations. For superohmic baths, the transition is due to the binding of the integer charges, while for subohmic baths, it is due to the binding of the half-integer charges, thereby signaling a dissipation-induced transition.

  1 citation

• Quenched random mass disorder in the large N theory of vector bosons

  Han Ma

  SciPost Phys. 14, 039 (2023) · published 17 March 2023 | Toggle abstract · pdf

  We study the critical bosonic O(N) vector model with quenched random mass disorder in the large N limit. Due to the replicated action which is sometimes not bounded from below, we avoid the replica trick and adopt a traditional approach to directly compute the disorder averaged physical observables. At $N=\infty$, we can exactly solve the disordered model. The resulting low energy behavior can be described by two scale invariant theories, one of which has an intrinsic scale. At finite $N$, we find that the previously proposed attractive disordered fixed point at $d=2$ continues to exist at $d=2+\epsilon$ spatial dimensions. We also studied the system in the $3<d<4$ spatial dimensions where the disorder is relevant at the Gaussian fixed point. However, no physical attractive fixed point is found right below four spatial dimensions. Nevertheless, the stable fixed point at $2+\epsilon$ dimensions can still survive at $d=3$ where the system has experimental realizations. Some critical exponents are predicted in order to be checked by future numerics and experiments.

  1 citation

• Probing pair correlations in Fermi gases with Ramsey-Bragg interferometry

  Théo Malas-Danzé, Alexandre Dugelay, Nir Navon, Hadrien Kurkjian

  SciPost Phys. 17, 024 (2024) · published 29 July 2024 | Toggle abstract · pdf

  We propose an interferometric method to probe pair correlations in a gas of spin-$1/2$ fermions. The method consists of a Ramsey sequence where both spin states of the Fermi gas are set in a superposition of a state at rest and a state with a large recoil velocity. The two-body density matrix is extracted via the fluctuations of the transferred fraction to the recoiled state. In the pair-condensed phase, the off-diagonal long-range order is directly reflected in the asymptotic behavior of the interferometric signal for long interrogation times. The method also allows to probe the spatial structure of the condensed pairs: the interferometric signal is an oscillating function of the interrogation time in the Bardeen-Cooper-Schrieffer regime; it becomes an overdamped function in the molecular Bose-Einstein condensate regime.

  1 citation

• TorchGDM: A GPU-accelerated Python toolkit for multi-scale electromagnetic scattering with automatic differentiation

  Sofia Ponomareva, Adelin Patoux, Clément Majorel, Antoine Azéma, Aurélien Cuche, Christian Girard, Arnaud Arbouet, Peter R. Wiecha

  SciPost Phys. Codebases 60 (2025) · published 22 October 2025 | Toggle abstract · pdf

  We present "torchGDM", a numerical framework for nano-optical simulations based on the Green's Dyadic Method (GDM). This toolkit combines a hybrid approach, allowing for both fully discretized nano-structures and structures approximated by sets of effective electric and magnetic dipoles. It supports simulations in three dimensions and for infinitely long, two-dimensional structures. This capability is particularly suited for multi-scale modeling, enabling accurate near-field calculations within or around a discretized structure embedded in a complex environment of scatterers represented by effective models. Importantly, torchGDM is entirely implemented in PyTorch, a well-optimized and GPU-enabled automatic differentiation framework. This allows for the efficient calculation of exact derivatives of any simulated observable with respect to various inputs, including positions, wavelengths or permittivity, but also intermediate parameters like Green's tensor components, which can be interesting for physics informed deep learning applications. We anticipate that this toolkit will be valuable for applications merging nano-photonics and machine learning, as well as for solving nano-photonic optimization and inverse problems, such as the global design and characterization of metasurfaces, where optical interactions between structures are critical.

  1 citation

• Searches for additional Higgs bosons decaying to tau leptons at the LHC

  Claudio Caputo on behalf of the ATLAS an CMS collaborations

  SciPost Phys. Proc. 1, 022 (2019) · published 20 February 2019 | Toggle abstract · pdf

  The searches for additional Higgs bosons decaying to tau leptons in scenarios beyond the standard model will be summarised, from the pp collision data collected by the ATLAS and CMS experiments at LHC Run-2.

  1 citation

• Smuggling critique into impact: Research design principles for critical and actionable migration research

  Maybritt Jill Alpes

  Mig. Pol. 4, 004 (2025) · published 12 June 2025 | Toggle abstract · pdf

  This article introduces critical and actionable migration research as an approach for scholars seeking to mobilize their epistemic resources to resist migration laws and policies that violate human rights principles in the short and medium term. While academia is increasingly shaped by a neoliberal “impact agenda,” violence at physical and administrative borders, as well human rights violations continue to intensify - raising questions about the potential role of academic knowledge in resisting these dynamics. Using ideal types as simplified analytical constructs, the article suggests that the limited transformative potential of academic knowledge stems from a persistant dichotomy: applied research is often not critical and critical research is often not actionable. Overcoming this dichotomy, critical and actionable migration research advances structural transformations and reframes while simultaneously remaining actionable for state actors in the short and medium term. As such, critical and actionable migration research is not applied research, nor devoid of theoretical considerations. Using the metaphor of smuggling, this article asks how migration researchers can reclaim the meaning of “impact” so that it contains the grains of critique that resist border violence and human rights violations in the short and medium term. The article’s answer is based on autobiographical explorations of what it means for an anthropologist to produce knowledge on migration from within law faculties and as policy officer and research consultant for human and refugee rights organizations. Based on this material, the article argues that “impact” is nothing to be “done” once the research is completed. To engage in critical and actionable migration research, scholars should instead theorize transformative knowledge encounters between academics and practitioners as integral parts of the research design. After a discussion of the autobiographical data and a conceptual discussion of transformative knowledge encounters, the article highlights three specific research design principles for critical and actionable migration research: (1) building innovative knowledge alliances, (2) theorizing knowledge needs, and (3) brokering the validity of truth claims.

  1 citation

• Codebase release 1.0 for TorchGPE

  Lorenzo Fioroni, Luca Gravina, Justyna Stefaniak, Alexander Baumgärtner, Fabian Finger, Davide Dreon, Tobias Donner

  SciPost Phys. Codebases 38-r1.0 (2024) · published 6 November 2024 | Toggle abstract · src

  TorchGPE is a general-purpose Python package developed for solving the Gross-Pitaevskii equation (GPE). This solver is designed to integrate wave functions across a spectrum of linear and non-linear potentials. A distinctive aspect of TorchGPE is its modular approach, which allows the incorporation of arbitrary self-consistent and time-dependent potentials, e.g., those relevant in many-body cavity QED models. The package employs a symmetric split-step Fourier propagation method, effective in both real and imaginary time. In our work, we demonstrate a significant improvement in computational efficiency by leveraging GPU computing capabilities. With the integration of the latter technology, TorchGPE achieves a substantial speed-up with respect to conventional CPU-based methods, greatly expanding the scope and potential of research in this field.

  1 citation

• Simulation of the 1d XY model on a quantum computer

  Marc Farreras, Alba Cervera-Lierta

  SciPost Phys. Lect. Notes 95 (2025) · published 11 June 2025 | Toggle abstract · pdf

  The field of quantum computing has grown fast in recent years, both in theoretical advancements and the practical construction of quantum computers. These computers were initially proposed, among other reasons, to efficiently simulate and comprehend the complexities of quantum physics. In this paper, we present a comprehensive scheme for the exact simulation of the 1-D XY model on a quantum computer. We successfully diagonalize the proposed Hamiltonian, enabling access to the complete energy spectrum. Furthermore, we propose a novel approach to design a quantum circuit to perform exact time evolution. Among all the possibilities this opens, we compute the ground and excited state energies for the symmetric XY model with spin chains of $n=4$ and $n=8$ spins. Further, we calculate the expected value of transverse magnetization for the ground state in the transverse Ising model. Both studies allow the observation of a quantum phase transition from an antiferromagnetic to a paramagnetic state. Additionally, we have simulated the time evolution of the state all spins up in the transverse Ising model. The scalability and high performance of our algorithm make it an ideal candidate for benchmarking purposes, while also laying the foundation for simulating other integrable models on quantum computers.

  1 citation

• Codebase release 2.0 for sauce

  Caleb Marshall

  SciPost Phys. Codebases 37-r2.0 (2024) · published 6 November 2024 | Toggle abstract · src

  Low energy nuclear physics experiments are transitioning towards fully digital data acquisition systems. Realizing the gains in flexibility afforded by these systems relies on equally flexible data reduction techniques. In this paper, methods utilizing data frames and in-memory techniques to work with data, including data from self-triggering, digital data acquisition systems, are discussed within the context of a Python package, sauce. It is shown that data frame operations can encompass common analysis needs and allow interactive data analysis. Two event building techniques, dubbed referenced and referenceless event building, are shown to provide a means to transform raw list mode data into correlated multi-detector events. These techniques are demonstrated in the analysis of two example data sets.

  1 citation

• Implementing Transverse Momentum Dependent splitting functions in Parton Branching evolution equations

  Lissa Keersmaekers

  SciPost Phys. Proc. 8, 127 (2022) · published 13 July 2022 | Toggle abstract · pdf

  The Parton Branching (PB) approach describes the evolution of transverse momentum dependent (TMD) parton densities. We propose to extend the PB method by including TMD splitting functions, instead of the DGLAP splitting functions which assume strong ordering in transverse momentum. We present the evolution equations and their numerical solution, which is the first Monte Carlo implementation including TMD splitting functions.

  1 citation