arXiv subjects

Clément Berthière

Publications and source records attributed to Clément Berthière.

3 recordsLinked to original sources

arXiv2026

Genuine multientropy, dihedral invariants and Lifshitz theory

Multi-invariants are local-unitary invariants of state replicas introduced as potential probes of multipartite entanglement and correlations in quantum many-body systems. In this paper, we investigate two multi-invariants for tripartite pure states, namely multientropy and dihedral invariant. We compute the (genuine) multientropy for Lifshitz groundstates, and obtain its analytical continuation to noninteger values of Rényi index. We show that the genuine multientropy can be expressed in terms of mutual information and logarithmic negativity, a relation that also holds for stabilizer states. For general tripartite pure states, we demonstrate that dihedral invariants are related to Rényi reflected entropies. In particular, we show that the dihedral permutations of replicas are equivalent to the reflected construction, or alternatively to the realignment of density matrices.

hep-th↗

arXiv2025

Geometric expansion of fluctuations and average shadows

Fluctuations of observables provide unique insights into the nature of physical systems, and their study stands as a cornerstone of both theoretical and experimental science. Generalized fluctuations, or cumulants, provide information beyond the mean and variance of an observable. In this paper, we develop a systematic method to determine the asymptotic behavior of cumulants of local observables as the region becomes large. Our analysis reveals that the expansion is closely tied to the geometric characteristics of the region and its boundary, with coefficients given by convex moments of the connected correlation function: the latter is integrated against intrinsic volumes of convex polytopes built from the coordinates, which can be interpreted as average shadows. A particular application of our method shows that, in two dimensions, the leading behavior of odd cumulants of conserved quantities is topological, specifically depending on the Euler characteristic of the region. We illustrate these results with the paradigmatic strongly-interacting system of two-dimensional quantum Hall state at filling fraction $1/2$, by performing Monte-Carlo calculations of the skewness (third cumulant) of particle number in the Laughlin state.

cond-mat.str-el↗

arXiv2013

Quantum spindown of highly magnetized neutron stars

Pulsars are highly magnetized and rapidly rotating neutron stars. The magnetic field can reach the critical magnetic field from which quantum effects of the vacuum becomes relevant, giving rise to magnetooptic properties of vacuum characterized as an effective non linear medium. One spectacular consequence of this prediction is a macroscopic friction that leads to an additional contribution in the spindown of pulsars. In this paper, we highlight some observational consequences and in particular derive new constraints on the parameters of the Crab pulsar and J0540-6919.

astro-ph.HE↗