Publications

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Experimental protocol for observing single quantum many-body scars with transmon qubits

Peter Græns Larsen, Anne E. B. Nielsen, André Eckardt, Francesco Petiziol

SciPost Phys. 20, 036 (2026) · published 9 February 2026 | · pdf

Quantum many-body scars are energy eigenstates which fail to reproduce thermal expectation values of local observables, in systems where the rest of the many-body spectrum fulfils eigenstate thermalization. Experimental observation of quantum many-body scars has so far been limited to models with multiple scar states evenly spaced in energy. It is thus an interesting question whether even single isolated scars, which theoretically embody the weakest possibile violation of eigenstate thermalization and may be thought to have no detectable impact in experiments, can leave a trace in measurable quantities. Moreover, single scars offer an interesting scenario for exploring the connection between quantum many-body scars and the original notion of scarring in quantum dynamical systems theory. Here we propose protocols to observe single scars in architectures of fixed-frequency, fixed-coupling superconducting qubits. We first adapt known models possessing the desired features into a form particularly suited for the experimental platform. We develop protocols for the implementation of these models, through trotterized sequences of two-qubit cross-resonance interactions, and verify the existence of the approximate scar state in the stroboscopic effective Hamiltonian. Since a single scar cannot be detected from coherent revivals in the dynamics, differently from towers of scar states, we propose and numerically investigate alternative and experimentally-accessible signatures. These include the dynamical response of the scar to local state deformations, to controlled noise, and to the resolution of the Lie-Suzuki-Trotter digitization.
Electron charge dynamics and charge separation: A response theory approach

Lionel Lacombe, Lucia Reining, Vitaly Gorelov

SciPost Phys. 20, 035 (2026) · published 9 February 2026 | · pdf

This study applies response theory to investigate electron charge dynamics, with a particular focus on charge separation. We analytically assess the strengths and limitations of linear and quadratic response theories in describing charge density and current, illustrated by a model that simulates charge transfer systems. While linear response accurately captures optical properties, the quadratic response contains the minimal ingredients required to describe charge dynamics and separation. Notably, it closely matches exact time propagation results in some regime that we identify. We propose and test several approximations to the quadratic response and explore the influence of higher-order terms and the effect of on-site and nearest-neighbour interactions $U$ and $V$.
From data to the analytic S-matrix: A Bootstrap fit of the pion scattering amplitude

Andrea Guerrieri, Kelian Häring, Ning Su

SciPost Phys. 20, 034 (2026) · published 9 February 2026 | · pdf

Quantum Chromodynamics (QCD) governs the strong interactions of hadrons, but extracting its physical spectrum remains a significant challenge due to its non-perturbative nature. In this Letter, we introduce a novel data-driven approach that systematically enforces the fundamental principles of analyticity, crossing symmetry, and unitarity while fitting experimental data. Our Bootstrap Fit method combines S-matrix Bootstrap techniques with non-convex numerical optimization, allowing for the construction of a scattering amplitude that adheres to first-principles constraints. We apply this framework to pion-pion scattering, demonstrating that it accurately reproduces low-energy predictions from Chiral Perturbation Theory ($\chi$PT) while also providing a non-perturbative determination of the total cross-section that is consistent with experiment. A key feature of our approach is its ability to dynamically generate physical states, yielding a spectrum of resonances consistent with QCD. Most notably, we predict the existence of a genuine doubly charged tetraquark resonance around 2 GeV, which could be observed in B-meson decays at LHCb. These results establish a robust new pathway for extracting hadronic properties directly from scattering data while enforcing fundamental physical constraints.
Multispecies totally asymmetric simple exclusion process with long-range swap

Eunghyun Lee

SciPost Phys. Core 9, 008 (2026) · published 9 February 2026 | · pdf

We introduce the multispecies totally asymmetric simple exclusion process (mTASEP) with long-range swap, a new interacting particle system combining the backward-push rule with the forward-jump rule. Although governed by local dynamics, the model induces effective long-range particle exchanges. We establish its integrability by proving two-particle reducibility and showing that the associated scattering matrix satisfies the Yang-Baxter equation. In addition, we derive explicit contour integral formulas for transition probabilities. These results position the long-range swap model as a novel exactly solvable multispecies process, characterized by distinctive algebraic features and opening new directions for further study in integrable probability and statistical mechanics.
Low energy effective theories of composite dark matter with real representations

Joachim Pomper, Suchita Kulkarni

SciPost Phys. Core 9, 007 (2026) · published 6 February 2026 | · pdf

We consider pseudo Nambu-Goldstone bosons arising from Dirac fermions transforming in real representations of a confining gauge group as dark matter candidates. We consider a special case of two Dirac fermions and couple the resulting dark sector to the Standard Model using a vector mediator. Within this construction, we develop a consistent low energy effective theory, with special attention to Wess-Zumino-Witten term given the topologically non-trivial coset space. We furthermore include the heavier spin-0 flavour singlet state and the spin-1 vector meson multiplet, by using the Hidden Local Symmetry Lagrangian for the latter. Although we concentrate on special case of two flavours, our results are generic and can be applied to a wider variety of theories featuring real representations. We apply our formalism and comment on the effect of the flavour singlet for dark matter phenomenology. Finally, we also comment on generalisation of our formalism for higher representations and provide potential consequences of discrete symmetry breaking.
Matrix models for extremal and integrated correlators of higher rank

Alba Grassi, Cristoforo Iossa

SciPost Phys. 20, 033 (2026) · published 5 February 2026 | · pdf

We study extremal and integrated correlators of half-BPS operators in four-dimensional $\mathcal{N}=2$ SQCD and $\mathcal{N}=4$ SYM with ${\rm SU}(3)$ gauge group. We focus on the large R-charge sector where the number of operators insertions becomes very large. In this regime, we demonstrate that the correlators are described by a combination of Wishart and Jacobi matrix models, coupled in a non-trivial way. The size of the matrices in each model corresponds to the maximal number of insertions for each of the two single trace generators. This dual matrix model representation allows us to extract the behavior of the correlators at weak and strong coupling in a 't Hooft-like double scaling limit, including nonperturbative corrections. Although this work focuses on ${\rm SU}(3)$, we expect that our techniques can be extended to ${\rm SU}(N)$ for $N>3$ as well.
Multichannel topological Kondo models and their low-temperature conductances

Guangjie Li, Elio J. König, Jukka I. Väyrynen

SciPost Phys. 20, 032 (2026) · published 5 February 2026 | · pdf

In the multichannel Kondo effect, overscreening of a magnetic impurity by conduction electrons leads to a frustrated exotic ground state. It has been proposed that multichannel topological Kondo (MCTK) model involving topological Cooper pair boxes with $M$ Majorana modes [SO($M$) "spin"] and $N$ spinless electron channels exhibits an exotic intermediate coupling fixed point. This intermediate fixed point has been analyzed through large-$N$ perturbative calculations, which gives a zero-temperature conductance decaying as $1/N^2$ in the large-$N$ limit. However, the conductance at this intermediate fixed point has not been calculated for generic $N$. Using representation theory, we verify the existence of this intermediate-coupling fixed point and find the strong-coupling effective Hamiltonian for the case $M=4$. Using conformal field theory techniques for SO($M$), we generalize the notion of overscreening and conclude that the MCTK model is an overscreened Kondo model. We find the fixed-point finite-size energy spectrum and the leading irrelevant operator (LIO). We express the fixed-point conductance in terms of the modular S-matrix of SO($M$) for general $N$, confirming the previous large-$N$ result. We describe the finite-temperature corrections to the conductance by the LIO and find that they are qualitatively different for the cases $N=1$ and $N≥2$ due to the different fusion outcomes with the current operator. We also compare the multichannel topological Kondo model to the topological symplectic Kondo model.
Simulating the interplay of dipolar and quadrupolar interactions in NMR by spin dynamic mean-field theory

Timo Gräßer, Götz S. Uhrig

SciPost Phys. 20, 031 (2026) · published 4 February 2026 | · pdf

The simulation of nuclear magnetic resonance (NMR) experiments is a notoriously difficult task, if many spins participate in the dynamics. The recently established dynamic mean-field theory for high-temperature spin systems (spinDMFT) represents an efficient yet accurate method to deal with this scenario. SpinDMFT reduces a complex lattice system to a time-dependent single-site problem, which can be solved numerically with small computational effort. Since the approach retains local quantum degrees of freedom, a quadrupolar term can be exactly incorporated. This allows us to study the interplay of dipolar and quadrupolar interactions for any parameter range, i.e., without the need for a perturbative treatment. We obtain a remarkable agreement with experimental data for an aluminium nitride monocrystal, which strongly suggests the use of spinDMFT as a prediction tool. Furthermore, we draw a comparison between a quantum-mechanical and a classical version of spinDMFT showing that local quantum effects are of great importance for the studied type of system.
Modelling $b\bar b H$ production for the LHC at 13.6 TeV

Christian Biello, Alessandro Gavardi, Rebecca von Kuk, Matthew A. Lim, Stefano Manzoni, Elena Mazzeo, Javier Mazzitelli, Aparna Sankar, Michael Spira, Frank J. Tackmann, Marius Wiesemann, Giulia Zanderighi, Marco Zaro

SciPost Phys. Comm. Rep. 18 (2026) · published 4 February 2026 | · pdf

We present new state-of-the-art predictions for Standard Model Higgs boson production in association with a bottom-quark pair ($b\bar bH$). Updated cross sections are computed in accordance with the recommendations of the LHC Higgs Working Group, including the use of the PDF4LHC21 set of parton distribution functions, with a center-of-mass energy of 13.6 TeV. For the total inclusive cross section, we provide matched predictions of the massless five-flavour scheme (5FS) and the massive four-flavour scheme (4FS) at the fixed-order level. We further present recently obtained simulations matched with parton showers in both flavour schemes within the SM, and also discuss them in the context of potential BSM scenarios. In the massless scheme, we compare different NNLO+PS predictions obtained through the MiNNLOPS and GENEVA generators. In addition, the role of 4FS predictions is studied as a background to $HH$ searches, considering both the top-quark and bottom-quark Yukawa contributions to $b\bar bH$ production. Finally, we analyse the sensitivity of the Higgs transverse momentum spectrum to light-quark Yukawa couplings in the diphoton decay channel based on MiNNLOPS simulations.
Superconducting diode effect in a meso-wedge geometry with Abrikosov vortices

Cristhian A. Aguirre, Jose Barba-Ortega, Alberto S. de Arruda, Julian Faundez

SciPost Phys. Core 9, 006 (2026) · published 4 February 2026 | · pdf

In this study, we explore the behavior of a superconducting meso-wedge geometry in 3+1 dimensions (three spatial dimensions plus time) subjected to external transport currents at its boundaries and surfaces, as well as external fields applied along the $\hat{z}$-direction. The transport currents are included as two opposite polarities, $J>0$ and $J<0$, respectively. Using the generalized time-dependent Ginzburg-Landau theory and considering the order parameter $\kappa$, we focus on two scenarios: a fixed external magnetic field with variable $\kappa$, and fixed $\kappa$ with variable external magnetic field. As a result, under both scenarios, we analyze the voltage-current characteristics of the superconducting meso-wedge, finding that the critical currents differ between polarities, demonstrating the system's non-reciprocity. We further examine the efficiency of the diode as a function of $\kappa$ and the external magnetic field applied. Furthermore, our observations reveal that the current polarity strongly influences the vortex configuration, the parameter $\kappa$, and the applied magnetic field. In particular, the formation of Abrikosov-type vortices exhibits pronounced inhomogeneity depending on the direction of the transport currents. This underscores that the diode effect in the superconducting meso-wedge is intimately associated with the anisotropic nucleation of Abrikosov vortices. Notably, the emergence of polarity-dependent vortex patterns can serve as a distinctive hallmark of the diode effect in these superconducting meso-wedge geometries.

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