Publications

Order by: publication date number of citations

• Quantum chaos in PT symmetric quantum systems

  Kshitij Sharma, Himanshu Sahu, Subroto Mukerjee

  SciPost Phys. 19, 120 (2025) · published 7 November 2025 | Toggle abstract · pdf

  In this study, we explore the interplay between $\mathcal{PT}$-symmetry and quantum chaos in a non-Hermitian dynamical system. We consider an extension of the standard diagnostics of quantum chaos, namely the complex level spacing ratio and out-of-time-ordered correlators (OTOCs), to study the $\mathcal{PT}$-symmetric quantum kicked rotor model. The kicked rotor has long been regarded as a paradigmatic dynamic system to study classical and quantum chaos. By introducing non-Hermiticity in the quantum kicked rotor, we uncover new phases and transitions that are absent in the Hermitian system. From the study of the complex level spacing ratio, we locate three regimes – one which is integrable and $\mathcal{PT}$-symmetry, another which is chaotic with $\mathcal{PT}$-symmetry and a third which is chaotic but with broken $\mathcal{PT}$-symmetry. We find that the complex level spacing ratio can distinguish between all three phases. Since calculations of the OTOC can be related to those of the classical Lyapunov exponent in the semi-classical limit, we investigate its nature in these regimes and at the phase boundaries. In the phases with $\mathcal{PT}$-symmetry, the OTOC exhibits behaviour akin to what is observed in the Hermitian system in both the integrable and chaotic regimes. Moreover, in the $\mathcal{PT}$-symmetry broken phase, the OTOC demonstrates additional exponential growth stemming from the complex nature of the eigenvalue spectrum at later times. We derive the analytical form of the late-time behaviour of the OTOC. By defining a normalized OTOC to mitigate the effects caused by $\mathcal{PT}$-symmetry breaking, we show that the OTOC exhibits singular behaviour at the transition from the $\mathcal{PT}$-symmetric chaotic phase to the $\mathcal{PT}$-symmetry broken, chaotic phase.

• Learning selection cuts with gradients

  Mike Hance, Juan Robles

  SciPost Phys. Core 8, 079 (2025) · published 7 November 2025 | Toggle abstract · pdf

  Many analyses in high-energy physics rely on selection thresholds (cuts) applied to detector, particle, or event properties. Initial cut values can often be guessed from physical intuition, but cut optimization, especially for multiple features, is commonly performed by hand, or skipped entirely in favor of multivariate algorithms like BDTs or neural networks. We revisit this problem, and develop a cut optimization approach based on gradient descent. Cut thresholds are learned as parameters of a network with a simple architecture, and can be tuned to achieve a target signal efficiency through the use of custom loss functions. Contractive terms in the loss can be used to ensure a smooth evolution of cuts as functions of efficiency, particle kinematics, or event features. The method is used to classify events in a search for Supersymmetry, and the performance is compared with common classification tools. An implementation of this approach is available in a public code repository and python package.

• Rényi entropies for one-dimensional quantum systems with mixed boundary conditions

  Benoit Estienne, Yacine Ikhlef, Andrei Rotaru

  SciPost Phys. 19, 119 (2025) · published 6 November 2025 | Toggle abstract · pdf

  We present a general method for calculating Rényi entropies in the ground state of a one-dimensional critical system with mixed open boundaries, for an interval starting at one of its ends. Technically, we consider the case when the boundary operator implementing the change of boundary conditions is degenerate under the Virasoro algebra. By exploiting the null-vectors conditions, we derive the ordinary differential equations that govern the scaling functions associated to the entropies. In particular, we provide an explicit formula for the second Rényi entropy. Additionally, we identify and compute the leading finite-size corrections to compare our theoretical results with numerical data for the Ising and three-state Potts critical chains.

• Magic phase transition and non-local complexity in generalized W State

  Alberto Giuseppe Catalano, Jovan Odavić, Gianpaolo Torre, Alioscia Hamma, Fabio Franchini, Salvatore Marco Giampaolo

  SciPost Phys. Core 8, 078 (2025) · published 6 November 2025 | Toggle abstract · pdf

  We employ the Stabilizer Rényi Entropy (SRE) to characterize a quantum phase transition that has so far eluded any standard description and can thus now be explained in terms of the interplay between its non-stabilizer properties and entanglement. The transition under consideration separates a region with a unique ground state from one with a degenerate ground state manifold spanned by states with finite and opposite (intensive) momenta. We show that SRE has a jump at the crossing points, while the entanglement entropy remains continuous. Moreover, by leveraging a Clifford circuit mapping, we connect the observed jump in SRE to that occurring between standard and generalized $W$-states with finite momenta. This mapping allows us to quantify the SRE discontinuity analytically.

• calcQPI: A versatile tool to simulate quasiparticle interference

  Peter Wahl, Luke C. Rhodes, Carolina A. Marques

  SciPost Phys. Codebases 61 (2025) · published 5 November 2025 | Toggle abstract · pdf

  Quasiparticle interference imaging (QPI) provides a route to characterize electronic structure from real space images acquired using scanning tunneling microscopy. It emerges due to scattering of electrons at defects in the material. The QPI patterns encode details of the $k$-space electronic structure and its spin and orbital texture. Recovering this information from a measurement of QPI is non-trivial, requiring modelling not only of the dominant scattering vectors, but also the overlap of the wave functions with the tip of the microscope. While, in principle, it is possible to model QPI from density functional theory (DFT) calculations, for many quantum materials it is more desirable to model the QPI from a tight-binding model, where inaccuracies of the DFT calculation can be corrected. Here, we introduce an efficient code to simulate quasiparticle interference from tight-binding models using the continuum Green's function method.

  1 citation

• Codebase release 1.0 for calcQPI

  Peter Wahl, Luke C. Rhodes, Carolina A. Marques

  SciPost Phys. Codebases 61-r1.0 (2025) · published 5 November 2025 | Toggle abstract · src

  Quasiparticle interference imaging (QPI) provides a route to characterize electronic structure from real space images acquired using scanning tunneling microscopy. It emerges due to scattering of electrons at defects in the material. The QPI patterns encode details of the $k$-space electronic structure and its spin and orbital texture. Recovering this information from a measurement of QPI is non-trivial, requiring modelling not only of the dominant scattering vectors, but also the overlap of the wave functions with the tip of the microscope. While, in principle, it is possible to model QPI from density functional theory (DFT) calculations, for many quantum materials it is more desirable to model the QPI from a tight-binding model, where inaccuracies of the DFT calculation can be corrected. Here, we introduce an efficient code to simulate quasiparticle interference from tight-binding models using the continuum Green's function method.

  1 citation

• Higgs production via vector-boson fusion at the LHC

  Gaetano Barone, Jiayi Chen, Stephane Cooperstein, Nikita Dolganov, Silvia Ferrario Ravasio, Yacine Haddad, Stefan Höche, Barbara Jäger, Alexander Karlberg, Alexander Mück, Mathieu Pellen, Christian T. Preuss, Daniel Reichelt, Simon Reinhardt, Marco Zaro

  SciPost Phys. Comm. Rep. 13 (2025) · published 5 November 2025 | Toggle abstract · pdf

  In this article, we summarise the recent experimental measurements and theoretical work on Higgs boson production via vector-boson fusion at the LHC. Along with this, we provide state-of-the-art predictions at fixed order as well as with parton-shower corrections within the Standard Model at $13.6\,\text{TeV}$. The results are presented in the form of multi-differential distributions as well as in the Simplified Template Cross Section bins. All materials and outputs of this study are available on public repositories. Finally, following findings in the literature, recommendations are made to estimate theoretical uncertainties related to parton-shower corrections.

• Engineering of anyons on M5-probes via flux quantization

  Hisham Sati, Urs Schreiber

  SciPost Phys. Lect. Notes 107 (2025) · published 4 November 2025 | Toggle abstract · pdf

  These extended lecture notes survey a novel derivation of anyonic topological order (as seen in fractional quantum Hall systems) on single magnetized M5-branes probing Seifert orbi-singularities ("geometric engineering" of anyons), which we motivate from fundamental open problems in the field of quantum computing. The rigorous construction is non-Lagrangian and non-perturbative, based on previously neglected global completion of the M5-brane's tensor field by flux-quantization consistent with its non-linear self-duality and its twisting by the bulk C-field. This exists only in little-studied non-abelian generalized cohomology theories, notably in a twisted equivariant (and "twistorial") form of unstable Cohomotopy ("Hypothesis H"). As a result, topological quantum observables form Pontrjagin homology algebras of mapping spaces from the orbi-fixed worldvolume into a classifying 2-sphere. Remarkably, results from algebraic topology imply from this the quantum observables and modular functor of abelian Chern-Simons theory, as well as braid group actions on defect anyons of the kind envisioned as hardware for topologically protected quantum gates.

• On the generalized Komar charge of Kaluza-Klein theories and higher-form symmetries

  Gabriele Barbagallo, José Luis V. Cerdeira, Carmen Gómez-Fayrén, Patrick Meessen, Tomás Ortín

  SciPost Phys. Core 8, 077 (2025) · published 4 November 2025 | Toggle abstract · pdf

  The generalized Komar $(d-2)$-form charge can be modified by the addition of any other on-shell closed (conserved) $(d-2)$-form charge. We show that, with Kaluza–Klein boundary conditions, one has to add a charge related to the higher-form symmetry identified in Ref. [C. Gomez-Fayren et al., SciPost Phys. Core 8, 010 (2025)] to the naive Komar charge of pure 5-dimensional gravity to obtain a conserved charge whose integral at spatial infinity gives the mass. The new term also contains the contribution of the Kaluza–Klein monopole charge leading to electric-magnetic duality invariance.

• Parallel assembly of neutral atom arrays with an SLM using linear phase interpolation

  Ivo H. A. Knottnerus, Yu Chih Tseng (曾于誌), Alexander Urech, Robert J. C. Spreeuw, Florian Schreck

  SciPost Phys. 19, 118 (2025) · published 31 October 2025 | Toggle abstract · pdf

  We present fast parallel rearrangement of single atoms in optical tweezers into arbitrary geometries by updating holograms displayed by an ultra fast spatial light modulator. Using linear interpolation of the tweezer position and the optical phase between the start and end arrays, we can calculate and display holograms every few ms, limited by technology. To show the versatility of our method, we sort the same atomic sample into multiple geometries with success probabilities of $0.996(2)$ per rearrangement cycle. This makes the method a useful tool for rearranging large atom arrays for quantum computation and quantum simulation.