Publications

Order by: publication date number of citations

• On the boundary conformal field theory approach to symmetry-resolved entanglement

  Giuseppe Di Giulio, René Meyer, Christian Northe, Henri Scheppach, Suting Zhao

  SciPost Phys. Core 6, 049 (2023) · published 11 July 2023 | Toggle abstract · pdf

  We study the symmetry resolution of the entanglement entropy of an interval in two-dimensional conformal field theories (CFTs), by relating the bipartition to the geometry of an annulus with conformal boundary conditions. In the presence of extended symmetries such as Kac-Moody type current algebrae, symmetry resolution is possible only if the boundary conditions on the annulus preserve part of the symmetry group, i.e. if the factorization map associated with the spatial bipartition is compatible with the symmetry in question. The partition function of the boundary CFT (BCFT) is then decomposed in terms of the characters of the irreducible representations of the symmetry group preserved by the boundary conditions. We demonstrate that this decomposition already provides the symmetry resolution of the entanglement spectrum of the corresponding bipartition. Considering the various terms of the partition function associated with the same representation, or charge sector, the symmetry-resolved Rényi entropies can be derived to all orders in the UV cutoff expansion without the need to compute the charged moments. We apply this idea to the theory of a free massless boson with $U(1)$, $\mathbb{R}$ and $\mathbb{Z}_2$ symmetry.

  9 citations

• Exact one-particle density matrix for SU(N) fermionic matter-waves in the strong repulsive limit

  Andreas Osterloh, Juan Polo, Wayne J. Chetcuti, Luigi Amico

  SciPost Phys. 15, 006 (2023) · published 11 July 2023 | Toggle abstract · pdf

  We consider a gas of repulsive $N$-component fermions confined in a ring-shaped potential, subjected to an effective magnetic field. For large repulsion strengths, we work out a Bethe ansatz scheme to compute the two-point correlation matrix and then the one-particle density matrix. Our results hold in the mesoscopic regime of finite but sufficiently large number of particles and system size that are not accessible by numerics. We access the momentum distribution of the system and analyse its specific dependence of interaction, magnetic field and number of components $N$. In the context of cold atoms, the exact computation of the correlation matrix to determine the interference patterns that are produced by releasing cold atoms from ring traps is carried out.

• Delocalized states in three-terminal superconductor-semiconductor nanowire devices

  P. Yu, B. D. Woods, J. Chen, G. Badawy, E. P. A. M. Bakkers, T. D. Stanescu, S. M. Frolov

  SciPost Phys. 15, 005 (2023) · published 11 July 2023 | Toggle abstract · pdf

  We fabricate three-terminal hybrid devices consisting of a semiconductor nanowire segment proximitized by a grounded superconductor and having tunnel probe contacts on both sides. By performing simultaneous tunneling measurements, we identify delocalized states, which can be observed from both ends, and states localized near one of the tunnel barriers. The delocalized states can be traced from zero magnetic field to fields beyond 0.5 T. Within the regime that supports delocalized states, we search for correlated low-energy features consistent with the presence of Majorana zero modes. While both sides of the device exhibit ubiquitous low-energy features at high fields, no correlation is inferred. Simulations using a one-dimensional effective model suggest that the delocalized states, which extend throughout the whole system, have large characteristic wave vectors, while the lower momentum states expected to give rise to Majorana physics are localized by disorder. To avoid such localization and realize Majorana zero modes, disorder needs to be reduced significantly. We propose a method for estimating the disorder strength based on analyzing the level spacing between delocalized states.

  1 citation

• Alibis of Exclusion: The role of ethnic economies in the differentiated inclusion of refugees in Berlin

  Jagat Sohail

  Mig. Pol. 2, 002 (2023) · published 11 July 2023 | Toggle abstract · pdf

  Neoliberal transformations in the field of asylum in Germany have, since 2016, placed an emphasis on labour market participation as the primary way through which refugees can establish long-term residence claims. Yet, while new arrivals are increasingly expected to rapidly integrate into this market, they are often armed with differential and precarious legal statuses which overwhelmingly determine the spheres of economic activity refugees can enter. This is especially true for the ever increasing number of rejected asylum seekers who are temporarily “tolerated”, for whom the only path to residence requires that they display their value as economic subjects to the German state. Based on ethnographic fieldwork conducted in Berlin between 2017 and 2020, I argue that, armed with little other than their cultural identities and networks, many refugees heavily relied on co-ethnic relationships to facilitate their participation in the labour market. The result is a displacement of the management of new diversity to ethnic economies, a move that disavows the marginalising consequences of the neoliberal transformations refugees are subject to. By masking a relationship between recently arrived migrants and the German economy and society as a relationship between migrants themselves, I argue that these practices work as alibis of exclusion.

• Annihilating dark matter search with 12 years of Fermi LAT data in nearby galaxy clusters

  Charles Thorpe-Morgan, D. Malyshev, C.-A. Stegen, Andrea Santangelo, J. Jochum

  SciPost Phys. Proc. 12, 071 (2023) · published 10 July 2023 | Toggle abstract · pdf

  Galaxy clusters contain an abundance of dark matter making them attractive laboratories for indirect DM searches. This work details a search for signals of pair annihilation from WIMP dark matter in the GeV gamma ray regime. We perform this search in five low $z$ and high galactic latitude galaxy clusters (Centaurus, Coma, Virgo, Perseus and Fornax); using nearly 12 years of Fermi/LAT data. Through the non-detection of this characteristic signal, we derive constraints on the annihilation cross-section of DM pair annihilation into the $b\overline{b}$, $W^+W^-$ and $\gamma\gamma$ channels. The limits obtained are of a comparable magnitude to those of recently derived from Fermi/LAT observations of dwarf spheroidal galaxies.

• A simple coin for a 2d entangled walk

  Ahmadullah Zahed, Kallol Sen

  SciPost Phys. Core 6, 048 (2023) · published 10 July 2023 | Toggle abstract · pdf

  We analyze the effect of a simple coin operator, built out of Bell pairs, in a 2d Discrete Quantum Random Walk (DQRW) problem. The specific form of the coin enables us to find analytical and closed form solutions to the recursion relations of the DQRW. The coin induces entanglement between the spin and position degrees of freedom, which oscillates with time and reaches a constant value asymptotically. We probe the entangling properties of the coin operator further, by two different measures. First, by integrating over the space of initial tensor product states, we determine the Entangling Power of the coin operator. Secondly, we compute the Generalized Relative Rényi Entropy between the corresponding density matrices for the entangled state and the initial pure unentangled state. Both the Entangling Power and Generalized Relative Rényi Entropy behaves similar to the entanglement with time. Finally, in the continuum limit, the specific coin operator reduces the 2d DQRW into two 1d massive fermions coupled to synthetic gauge fields, where both the mass term and the gauge fields are built out of the coin parameters.

  1 citation

• Anomaly of $(2+1)$-dimensional symmetry-enriched topological order from $(3+1)$-dimensional topological quantum field theory

  Weicheng Ye, Liujun Zou

  SciPost Phys. 15, 004 (2023) · published 10 July 2023 | Toggle abstract · pdf

  Symmetry acting on a (2+1)$D$ topological order can be anomalous in the sense that they possess an obstruction to being realized as a purely (2+1)$D$ on-site symmetry. In this paper, we develop a (3+1)$D$ topological quantum field theory to calculate the anomaly indicators of a (2+1)$D$ topological order with a general symmetry group $G$, which may be discrete or continuous, Abelian or non-Abelian, contain anti-unitary elements or not, and permute anyons or not. These anomaly indicators are partition functions of the (3+1)$D$ topological quantum field theory on a specific manifold equipped with some $G$-bundle, and they are expressed using the data characterizing the topological order and the symmetry actions. Our framework is applied to derive the anomaly indicators for various symmetry groups, including $\mathbb{Z}_2\times\mathbb{Z}_2$, $\mathbb{Z}_2^T\times\mathbb{Z}_2^T$, $SO(N)$, $O(N)^T$, $SO(N)\times \mathbb{Z}_2^T$, etc, where $\mathbb{Z}_2$ and $\mathbb{Z}_2^T$ denote a unitary and anti-unitary order-2 group, respectively, and $O(N)^T$ denotes a symmetry group $O(N)$ such that elements in $O(N)$ with determinant $-1$ are anti-unitary. In particular, we demonstrate that some anomaly of $O(N)^T$ and $SO(N)\times \mathbb{Z}_2^T$ exhibit symmetry-enforced gaplessness, i.e., they cannot be realized by any symmetry-enriched topological order. As a byproduct, for $SO(N)$ symmetric topological orders, we derive their $SO(N)$ Hall conductance.

• Ruling out light axions: The writing is on the wall

  Konstantin A. Beyer, Subir Sarkar

  SciPost Phys. 15, 003 (2023) · published 10 July 2023 | Toggle abstract · pdf

  We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry. Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe. The network may be made unstable by invoking a "tilt" in the axion potential due to Planck scale suppressed non-renormalisable operators. Alternatively the random walk of the axion field during inflation can generate a "bias" favouring one of the degenerate vacua, but we find that this mechanism is in practice irrelevant. Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather low - thus e.g. ruling out the DFSZ axion with mass below $\sim$ 11 meV, where most experimental searches are in fact focused.

  9 citations

• Codebase release 0.1 for infstat

  Kyoungchul Kong, Konstantin T. Matchev, Stephen Mrenna, Prasanth Shyamsundar

  SciPost Phys. Codebases 14-r0.1 (2023) · published 7 July 2023 | Toggle abstract · src

  We propose an intuitive, machine-learning approach to multiparameter inference, dubbed the InferoStatic Networks (ISN) method, to model the score and likelihood ratio estimators in cases when the probability density can be sampled but not computed directly. The ISN uses a backend neural network that models a scalar function called the inferostatic potential $\varphi$. In addition, we introduce new strategies, respectively called Kernel Score Estimation (KSE) and Kernel Likelihood Ratio Estimation (KLRE), to learn the score and the likelihood ratio functions from simulated data. We illustrate the new techniques with some toy examples and compare to existing approaches in the literature. We mention en passant some new loss functions that optimally incorporate latent information from simulations into the training procedure.

  1 citation

• New machine learning techniques for simulation-based inference: InferoStatic nets, kernel score estimation, and kernel likelihood ratio estimation

  Kyoungchul Kong, Konstantin T. Matchev, Stephen Mrenna, Prasanth Shyamsundar

  SciPost Phys. Codebases 14 (2023) · published 7 July 2023 | Toggle abstract · pdf

  We propose an intuitive, machine-learning approach to multiparameter inference, dubbed the InferoStatic Networks (ISN) method, to model the score and likelihood ratio estimators in cases when the probability density can be sampled but not computed directly. The ISN uses a backend neural network that models a scalar function called the inferostatic potential $\varphi$. In addition, we introduce new strategies, respectively called Kernel Score Estimation (KSE) and Kernel Likelihood Ratio Estimation (KLRE), to learn the score and the likelihood ratio functions from simulated data. We illustrate the new techniques with some toy examples and compare to existing approaches in the literature. We mention en passant some new loss functions that optimally incorporate latent information from simulations into the training procedure.

  1 citation