Publications

Order by: publication date number of citations

• On the discrepancy between the FOPT and CIPT approaches for hadronic tau spectral function moments

  Andre H. Hoang, Christoph Regner

  SciPost Phys. Proc. 7, 005 (2022) · published 20 June 2022 | Toggle abstract · pdf

  The discrepancy between the FOPT and CIPT approaches for hadronic tau spectral function moments constitutes the major theoretical uncertainty for strong coupling determinations from tau decay data. We show that the discrepancy can be analytically understood since the Borel representations -- which have been assumed to be identical for both approaches previously -- differ in the presence of IR renormalons. This implies that the OPE condensate corrections are different for both approaches and that the discrepancy may eventually be reconciled. In the talk we explain the difference and some mathematical aspects of the FOPT and CIPT Borel representations and show numerical results.

  2 citations

• Engineering Gaussian states of light from a planar microcavity

  Mathias Van Regemortel, Sylvain Ravets, Atac Imamoglu, Iacopo Carusotto, Michiel Wouters

  SciPost Phys. 5, 013 (2018) · published 30 July 2018 | Toggle abstract · pdf

  Quantum fluids of light in a nonlinear planar microcavity can exhibit antibunched photon statistics at short distances due to repulsive polariton interactions. We show that, despite the weakness of the nonlinearity, the antibunching signal can be amplified orders of magnitude with an appropriate free-space optics scheme to select and interfere output modes. Our results are understood from the unconventional photon blockade perspective by analyzing the approximate Gaussian output state of the microcavity. In a second part, we illustrate how the temporal and spatial profile of the density-density correlation function of a fluid of light can be reconstructed with free-space optics. Also here the nontrivial (anti)bunching signal can be amplified significantly by shaping the light emitted by the microcavity.

  2 citations

• Unveiling the anatomy of mode-coupling theory

  Ilian Pihlajamaa, Vincent E. Debets, Corentin C. L. Laudicina, Liesbeth M. C. Janssen

  SciPost Phys. 15, 217 (2023) · published 29 November 2023 | Toggle abstract · pdf

  The mode-coupling theory of the glass transition (MCT) has been at the forefront of fundamental glass research for decades, yet the theory's underlying approximations remain obscure. Here we quantify and critically assess the effect of each MCT approximation separately. Using Brownian dynamics simulations, we compute the memory kernel predicted by MCT after each approximation in its derivation, and compare it with the exact one. We find that some often-criticized approximations are in fact very accurate, while the opposite is true for others, providing new guiding cues for further theory development.

  2 citations

• Generative invertible quantum neural networks

  Armand Rousselot, Michael Spannowsky

  SciPost Phys. 16, 146 (2024) · published 4 June 2024 | Toggle abstract · pdf

  Invertible Neural Networks (INN) have become established tools for the simulation and generation of highly complex data. We propose a quantum-gate algorithm for a Quantum Invertible Neural Network (QINN) and apply it to the LHC data of jet-associated production of a Z-boson that decays into leptons, a standard candle process for particle collider precision measurements. We compare the QINN's performance for different loss functions and training scenarios. For this task, we find that a hybrid QINN matches the performance of a significantly larger purely classical INN in learning and generating complex data.

  2 citations

• Functional renormalisation group approach to shell models of turbulence

  Côme Fontaine, Malo Tarpin, Freddy Bouchet, Léonie Canet

  SciPost Phys. 15, 212 (2023) · published 28 November 2023 | Toggle abstract · pdf

  Shell models are simplified models of hydrodynamic turbulence, retaining only some essential features of the original equations, such as the non-linearity, symmetries and quadratic invariants. Yet, they were shown to reproduce the most salient properties of developed turbulence, in particular universal statistics and multi-scaling. We set up the functional renormalisation group (FRG) formalism to study generic shell models. In particular, we formulate an inverse RG flow, which consists in integrating out fluctuation modes from the large scales (small wavenumbers) to the small scales (large wavenumbers), which is physically grounded and has long been advocated in the context of turbulence. Focusing on the Sabra shell model, we study the effect of both a large-scale forcing, and a power-law forcing exerted at all scales. We show that these two types of forcing yield different fixed points, and thus correspond to distinct universality classes, characterised by different scaling exponents. We find that the power-law forcing leads to dimensional (K41-like) scaling, while the large-scale forcing entails anomalous scaling.

  2 citations

• Sensitivity of a collisional single-atom spin probe

  Jens Nettersheim, Quentin Bouton, Daniel Adam, Artur Widera

  SciPost Phys. Core 6, 009 (2023) · published 16 February 2023 | Toggle abstract · pdf

  We study the sensitivity of a collisional single-atom probe for ultracold gases. Inelastic spin-exchange collisions map information about the gas temperature $T$ or external magnetic field $B$ onto the quantum spin-population of single-atom probes, and previous work showed enhanced sensitivity for short-time nonequilibrium spin dynamics [Phys. Rev. X 10, 011018 (2020)]. Here, we numerically investigate the steady-state sensitivity of such single-atom probes to various observables. We find that the probe shows distinct sensitivity maxima in the ($B,T$) parameter diagram, although the underlying spin-exchange rates scale monotonically with temperature and magnetic field. In parameter space, the probe generally has the largest sensitivity when sensing the energy ratio between thermal energy and Zeeman energy in an externally applied magnetic field, while the sensitivity to the absolute energy, i.e., the sum of kinetic and Zeeman energy, is low. We identify the parameters yielding sensitivity maxima for a given absolute energy, which we can relate to a direct comparison of the thermal Maxwell-Boltzmann distribution with the Zeeman-energy splitting. We compare our equilibrium results to nonequilibrium experimental results from a single-atom quantum probe, showing that the sensitivity maxima in parameter space qualitatively prevail also in the nonequilibrium dynamics, while a quantitative difference remains. Our work thereby offers a microscopic explanation for the properties and performance of this single-atom quantum probe, connecting thermodynamic properties to microscopic interaction mechanisms. Our results pave the way for optimization of quantum-probe applications in ($B,T$) parameter space beyond the previously shown boost by nonequilibrium dynamics.

  2 citations

• Quantum simulation of colour in perturbative quantum chromodynamics

  Herschel A. Chawdhry, Mathieu Pellen

  SciPost Phys. 15, 205 (2023) · published 24 November 2023 | Toggle abstract · pdf

  Quantum computers are expected to give major speed-ups for the simulation of quantum systems. In this work, we present quantum gates that simulate the colour part of the interactions of quarks and gluons in perturbative quantum chromodynamics (QCD). As a first application, we implement these circuits on a simulated noiseless quantum computer and use them to calculate colour factors for various examples of Feynman diagrams. This work constitutes a first key step towards a quantum simulation of generic scattering processes in perturbative QCD.

  2 citations

• Smearing of causality by compositeness divides dispersive approaches into exact ones and precision-limited ones

  Felipe J. Llanes-Estrada, Raúl Roldán-González

  SciPost Phys. Core 5, 016 (2022) · published 29 March 2022 | Toggle abstract · pdf

  Scattering off the edge of a composite particle or finite--range interaction can precede that off its center. An effective theory treatment with pointlike particles and contact interactions must find that the scattered experimental wave is slightly advanced, in violation of causality (the fundamental underlying theory being causal). In practice, partial--wave or other projections of multivariate amplitudes exponentially grow with ${\rm Im}(E)$, so that analyticity is not sufficient to obtain a dispersion relation for them, but only for a slightly modified function (the modified relations additionally connect different $J$). This can limit the precision of certain dispersive approaches to compositeness based on Cauchy's theorem. Awareness of this may be of interest to some dispersive tests of the Standard Model with hadrons, and to unitarization methods used to extend electroweak effective theories. Interestingly, the Inverse Amplitude Method is safe (as the inverse amplitude has the opposite, convergent behavior allowing contour closure). Generically, one-dimensional sum rules such as for the photon vacuum polarization, form factors or the Adler function are not affected by this uncertainty; nor are fixed-$t$ dispersion relations, cleverly constructed to avoid it and whose consequences are solid.

  2 citations

• Theory of Andreev blockade in a double quantum dot with a superconducting lead

  David Pekker, Po Zhang, Sergey M. Frolov

  SciPost Phys. 11, 081 (2021) · published 22 October 2021 | Toggle abstract · pdf

  A normal metal source reservoir can load two electrons onto a double quantum dot in the spin-triplet configuration. We show that if the drain lead of the dot is a spin-singlet superconductor, these electrons cannot form a Cooper pair and are blockaded on the double dot. We call this phenomenon Andreev blockade because it arises due to suppressed Andreev reflections. We identify transport characteristics unique to Andreev blockade. Most significantly, it occurs for any occupation of the dot adjacent to the superconductor, in contrast with the well-studied Pauli blockade which requires odd occupations. Andreev blockade is lifted if quasiparticles are allowed to enter the superconducting lead, but it should be observable in the hard gap superconductor-semiconductor devices. A recent experiment tests this model and finds support for several predictions made here [P. Zhang, H. Wu, J. Chen, S. A. Khan, P. Krogstrup, D. Pekker, and S. M. Frolov, arXiv:2102.03283 (2021)]. Andreev blockade should be considered in the design of topological quantum circuits, hybrid quantum bits and quantum emulators.

  2 citations

• BRST invariant formulation of the Bell-CHSH inequality in gauge field theories

  David Dudal, Philipe De Fabritiis, Marcelo Santos Guimaraes, Giovani Peruzzo, Silvio Paolo Sorella

  SciPost Phys. 15, 201 (2023) · published 23 November 2023 | Toggle abstract · pdf

  A study of the Bell-CHSH inequality in gauge field theories is presented. By using the Kugo-Ojima analysis of the BRST charge cohomology in Fock space, the Bell-CHSH inequality is formulated in a manifestly BRST invariant way. The examples of the free four-dimensional Maxwell theory and the Abelian Higgs model are scrutinized. The inequality is probed by using BRST invariant squeezed states, allowing for large Bell-CHSH inequality violations, close to Tsirelson's bound. An illustrative comparison with the entangled state of two $1/2$ spin particles in Quantum Mechanics is provided.

  2 citations