Publications

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Extracting electronic many-body correlations from local measurements with artificial neural networks

Faluke Aikebaier, Teemu Ojanen, Jose L. Lado

SciPost Phys. Core 6, 030 (2023) · published 17 April 2023 | · pdf

The characterization of many-body correlations provides a powerful tool for analyzing correlated quantum materials. However, experimental extraction of quantum entanglement in correlated electronic systems remains an open problem in practice. In particular, the correlation entropy quantifies the strength of quantum correlations in interacting electronic systems, yet it requires measuring all the single-particle correlators of a macroscopic sample. To circumvent this bottleneck, we introduce a strategy to obtain the correlation entropy of electronic systems solely from a set of local measurements. We show that, by combining local particle-particle and density-density correlations with a neural-network algorithm, the correlation entropy can be predicted accurately. Specifically, we show that for a generalized interacting fermionic model, our algorithm yields an accurate prediction of the correlation entropy from a set of noisy local correlators. Our work shows that the correlation entropy in interacting electron systems can be reconstructed from local measurements, providing a starting point to experimentally extract many-body correlations with local probes.

5 citations
Density induced vacuum instability

Reuven Balkin, Javi Serra, Konstantin Springmann, Stefan Stelzl, Andreas Weiler

SciPost Phys. 14, 071 (2023) · published 14 April 2023 | · pdf

We consider matter density effects in theories with a false ground state. Large and dense systems, such as stars, can destabilize a metastable minimum and allow for the formation of bubbles of the true minimum. We derive the conditions under which these bubbles form, as well as the conditions under which they either remain confined to the dense region or escape to infinity. The latter case leads to a phase transition in the universe at star formation. We explore the phenomenological consequences of such seeded phase transitions.

4 citations
Stochastic representation of the quantum quartic oscillator

Gennaro Tucci, Stefano De Nicola, Sascha Wald, Andrea Gambassi

SciPost Phys. Core 6, 029 (2023) · published 14 April 2023 | · pdf

Recent experimental advances have inspired the development of theoretical tools to describe the non-equilibrium dynamics of quantum systems. Among them an exact representation of quantum spin systems in terms of classical stochastic processes has been proposed. Here we provide first steps towards the extension of this stochastic approach to bosonic systems by considering the one-dimensional quantum quartic oscillator. We show how to exactly parameterize the time evolution of this prototypical model via the dynamics of a set of classical variables. We interpret these variables as stochastic processes, which allows us to propose a novel way to numerically simulate the time evolution of the system. We benchmark our findings by considering analytically solvable limits and providing alternative derivations of known results.
Entanglement evolution after a global quench across a conformal defect

Luca Capizzi, Viktor Eisler

SciPost Phys. 14, 070 (2023) · published 13 April 2023 | · pdf

We study the evolution of entanglement after a global quench in a one-dimensional quantum system with a localized impurity. For systems described by a conformal field theory, the entanglement entropy between the two regions separated by the defect grows linearly in time. Introducing the notion of boundary twist fields, we show how the slope of this growth can be related to the effective central charge that emerges in the study of ground-state entropy in the presence of the defect. On the other hand, we also consider a particular lattice realization of the quench in a free-fermion chain with a conformal defect. Starting from a gapped initial state, we obtain the slope via a quasiparticle ansatz and observe small discrepancies between the field theory and lattice results, which persist even in the limit of a vanishing gap.

4 citations
Four-quark scatterings in QCD I

Wei-jie Fu, Chuang Huang, Jan M. Pawlowski, Yang-yang Tan

SciPost Phys. 14, 069 (2023) · published 13 April 2023 | · pdf

We investigate dynamical chiral symmetry breaking and the emergence of mesonic bound states from the infrared dynamics of four-quark scatterings. Both phenomena originate from the resonant scalar-pseudoscalar channel of the four-quark scatterings, and we compute the functional renormalisation group (fRG) flows of the Fierz-complete four-quark interaction of up and down quarks with its $t$ channel momentum dependence. This is done in the isospin symmetric case, also including the flow of the quark two-point function. This system can be understood as the fRG analogues of the complete Bethe-Salpeter equations and quark gap equation. The pole mass of the pion is determined from both direct calculations of the four-quark flows in the Minkowski regime of momenta and the analytic continuation based on results in the Euclidean regime, which are consistent with each other.
Ether cleavage and chemical removal of SU-8

José M. Ripalda, Raquel Álvaro, María Luisa Dotor

SciPost Chem. 2, 001 (2023) · published 13 April 2023 | · pdf

The high chemical stability of SU-8 makes it irreplaceable for a wide range of applications, most notably as a lithography photoresist for micro and nanotechnology. This advantage becomes a problem when there is a need to remove SU-8 from the fabricated devices. Researchers have been struggling for two decades with this problem, and although a number of partial solutions have been found, this difficulty has limited the applications of SU-8. Here we demonstrate a fast, reproducible, and comparatively gentle method to chemically remove SU-8 photoresist. An ether cleavage mechanism for the observed reaction is proposed, and the hypothesis is tested with ab initio quantum chemical calculations. We also describe a complementary removal method based on atomic hydrogen inductively coupled plasma.
Bootstrapping traceless symmetric $O(N)$ scalars

Marten Reehorst, Maria Refinetti, Alessandro Vichi

SciPost Phys. 14, 068 (2023) · published 12 April 2023 | · pdf

We use numerical bootstrap techniques to study correlation functions of traceless symmetric tensors of $O(N)$ with two indices $t_{ij}$. We obtain upper bounds on operator dimensions for all the relevant representations and several values of $N$. We discover several families of kinks, which do not correspond to any known model and we discuss possible candidates. We then specialize to the case $N=4$, which has been conjectured to describe a phase transition in the antiferromagnetic real projective model $ARP^{3}$. Lattice simulations provide strong evidence for the existence of a second order phase transition, while an effective field theory approach does not predict any fixed point. We identify a set of assumptions that constrain operator dimensions to a closed region overlapping with the lattice prediction. The region is still present after pushing the numerics in the single correlator case or when considering a mixed system involving $t$ and the lowest dimension scalar singlet.

2 citations
Non-invertible defects in 5d, boundaries and holography

Jeremias Aguilera Damia, Riccardo Argurio, Eduardo Garcia-Valdecasas

SciPost Phys. 14, 067 (2023) · published 12 April 2023 | · pdf

We show that very simple theories of abelian gauge fields with a cubic Chern-Simons term in 5d have an infinite number of non-invertible codimension two defects. They arise by dressing the symmetry operators of the broken electric 1-form symmetry with a suitable topological field theory, for any rational angle. We further discuss the same theories in the presence of a 4d boundary, and more particularly in a holographic setting. There we find that the bulk defects, when pushed to the boundary, have various different fates. Most notably, they can become codimension one non-invertible defects of a boundary theory with an ABJ anomaly.

25 citations
Topological insulators and geometry of vector bundles

Alexander S. Sergeev

SciPost Phys. Lect. Notes 67 (2023) · published 12 April 2023 | · pdf

For a long time, band theory of solids has focused on the energy spectrum, or Hamiltonian eigenvalues. Recently, it was realized that the collection of eigenvectors also contains important physical information. The local geometry of eigenspaces determines the electric polarization, while their global twisting gives rise to the metallic surface states in topological insulators. These phenomena are central topics of the present notes. The shape of eigenspaces is also responsible for many intriguing physical analogies, which have their roots in the theory of vector bundles. We give an informal introduction to the geometry and topology of vector bundles and describe various physical models from this mathematical perspective.
Engineering a pure Dirac regime in ZrTe$_5$

Jorge I. Facio, Elisabetta Nocerino, Ion Cosma Fulga, Rafal Wawrzynczak, Joanna Brown, Genda Gu, Qiang Li, Martin Mansson, Yasmine Sassa, Oleh Ivashko, Martin v. Zimmermann, Felix Mende, Johannes Gooth, Stanislaw Galeski, Jeroen van den Brink, Tobias Meng

SciPost Phys. 14, 066 (2023) · published 11 April 2023 | · pdf

Real-world topological semimetals typically exhibit Dirac and Weyl nodes that coexist with trivial Fermi pockets. This tends to mask the physics of the relativistic quasiparticles. Using the example of ZrTe$_5$, we show that strain provides a powerful tool for in-situ tuning of the band structure such that all trivial pockets are pushed far away from the Fermi energy, but only for a certain range of Van der Waals gaps. Our results naturally reconcile contradicting reports on the presence or absence of additional pockets in ZrTe$_5$, and provide a clear map of where to find a pure three-dimensional Dirac semimetallic phase in the structural parameter space of the material.

1 citation

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