arXiv subjects

Kristian Hauser A. Villegas

Publications and source records attributed to Kristian Hauser A. Villegas.

10 recordsLinked to original sources

arXiv2026

Simulating Majorana fermions in black hole with Ising Models

Quantum field theory (QFT) in curved spacetime has led to profound predictions, including the Unruh effect and Hawking radiation, yet their direct observation remains extraordinarily challenging because of their extremely weak signatures. Here, we show that the transverse-field Ising model provides a quantum simulator for Majorana fermions in a Schwarzschild black hole background. Remarkably, different coordinate representations of the same spacetime-Schwarzschild, tortoise, Kruskal, and conformally flat-map onto distinct microscopic Ising spin models. Despite their microscopic differences, these models converge in the continuum limit to the same Majorana field theory, exhibiting an emergent form of general covariance. This provides a rare example of a fundamental symmetry of general relativity arising as an emergent property of a condensed matter system. We further demonstrate how black hole particle production can be simulated and detected through spin correlation measurements, and discuss experimental platforms capable of realizing these models. Our work establishes a practical route for investigating fermionic QFT in curved spacetime using controllable quantum many-body systems and tabletop experiments.

quant-ph↗

arXiv2026

Bosonization in $R$-paraparticle Luttinger models

Alternative theories of quantum statistics provide an avenue for exploring novel physics beyond bosons and fermions, yet experimental verification of their existence in nature proves a challenging task. Among these theories, it has recently been suggested that $R$ parastatistics can be realized as quasiparticle excitations in many-body systems. In this paper, we build on this idea by showing that signatures of $R$ parastatistics can be observed as flavor-charge separation in one-dimensional (1D) systems. We consider a generalized version of the Luttinger model (LM) and show that bosonization persists when the $R$ paraparticles have Fermi-surface-like structures. These $R$ parafermions can satisfy generalized exclusion principles beyond conventional Pauli's. We show that density waves of all $R$ parafermions can always be bosonized, but flavor waves act like bosons only for a certain subclass of $R$ parafermions. We derive the conditions for bosonization by analyzing the LM spectrum, showing that bosonization applies only to low-temperature systems. Signatures of flavor-charge separation then become apparent as distinct dispersion profiles when we turn on interparticle interactions. This points to potential observations of flavor-charge separation in 1D systems that host emergent $R$ paraparticles.

cond-mat.str-el↗

arXiv2025

Quantum geometric tensor in systems with fractional band dispersion

We investigate the quantum geometric tensor, which is comprised of the Berry curvature and quantum metric, in a generalized Dirac two-band system with non-integer dispersion $E(\mathbf{k})\sim k^α$. Our analysis reveals that this type of dispersion introduces significant and novel effects on quantum band geometry. We calculate the Berry curvature and observe its redistribution in momentum space as $α$ varies. Notably, despite this redistribution, the change in Chern number across topological transitions remains quantized as an integer, even for non-integer $α$. We illustrate the physical implications of this redistribution by computing the orbital magnetization. Furthermore, we demonstrate that the Berry curvature and quantum metric peak along the regions of momentum space where the energy band exhibits high curvature. While it is well-established that Berry curvature becomes highly concentrated at the band touching points, our findings indicate that they can also accumulate at sharp band corners, away from these band touching points. We further show that while the Berry curvature develops Dirac delta-like peaks away from $\mathbf{k}=0$, the Berry monopole, corresponding to the topological charge, remains located at the origin.

cond-mat.supr-con↗

arXiv2024

Holographic superfluid sound modes with bulk acoustic black hole

The sound modes of a flowing superfluid is described by the massless Klein-Gordon equation in an effective background metric. This effective background metric can be designed to mimick a black hole using the acoustic horizon. In this work, we study the AdS/CFT dual of the sound modes in the presence of an acoustic horizon in the bulk. Focusing on fluids with a purely radial flow, we derive the metric tensor for the effective acoustic spacetime and deduce a necessary condition for an acoustic black hole geometry to exist within the fluid. Using specific examples of superfluid velocity profiles, we obtained the source, operator expectation value, Green's function, and spectral density of the dual field theory by solving for the asymptotic behavior of the sound modes near the AdS boundary. In all our examples, the sound modes remain gapless but the excitations are described by branch cuts, instead of poles, which is typical of strongly coupled systems. Furthermore, we calculate the effective Hawking temperature of the dual field theory associated with the bulk acoustic horizon. Lastly, we investigate the near horizon properties and derive the superfluid velocity profile that can give rise to an infrared emergent quantum criticality.

physics.gen-ph↗

arXiv2024

Quantum and higher curvature corrections to the anti-de Sitter black hole

Black holes exert quantum pressure coming from the nonlocal gravity correction. We investigate this nonlocal correction for black holes in anti-de Sitter (AdS) spacetime and its dual boundary field theory. We show that the second order curvature and the nonlocal actions do not backreact on the AdS black hole metric. Thus, the interpretation of quantum pressure holds in the bulk for AdS black hole, generalizing the previous result for the asymptotically flat black hole. We then show that the leading geometric correction comes from the third order in curvature and explicitly calculate the corrections to the metric and to the horizon. For applications to AdS/CFT, we conjectured a nonlocal Gibbons-Hawking-York boundary term along with the necessary counter terms to cancel the ultraviolet divergence of the bulk action. We then calculate the thermodynamic quantities in the bulk and discuss their properties.

gr-qc↗

arXiv2021

Anomalous Higgs oscillations mediated by Berry curvature and quantum metric

Higgs spectroscopy, the study of Higgs bosons of a superconductor, is an emerging field in studying superconductivity. Here we show that the Berry curvature and the quantum metric of bands play a central role in the Higgs mode generation. They allow the detection of Higgs bosons even when the conventional contribution from the band curvature vanishes. Furthermore, we show that the Higgs mode can couple to the external electromagnetic field linearly when mediated by the Berry connection. As a result, we predict the existence of a second harmonic generation, in addition to the well-known third harmonic generation. We elucidate our theory further by considering a flat band superconductor realized by the Harper-Hubbard model and show that the geometric Higgs mode is lower bounded by the band Chern number. We demonstrate in twisted bilayer graphene the existence of the geometrically induced Higgs modes when superconductivity is realized in the nearly flat band at the magic angle.

cond-mat.supr-con↗

arXiv2020

Optical Transistor for an Amplification of Radiation in a Broadband THz Domain

We propose a new type of optical transistor for a broadband amplification of THz radiation. It is made of a graphene--superconductor hybrid, where electrons and Cooper pairs couple by Coulomb forces. The transistor operates via the propagation of surface plasmons in both layers, and the origin of amplification is the quantum capacitance of graphene. It leads to THz waves amplification, the negative power absorption, and as a result, the system yields positive gain, and the hybrid acts like an optical transistor, operating with the terahertz light. It can, in principle, amplify even a whole spectrum of chaotic signals (or noise), that is required for numerous biological applications.

physics.app-ph↗

arXiv2019

Unconventional Bloch-Grüneisen scattering in hybrid Bose-Fermi systems

We report on the novel mechanism of electron scattering in hybrid Bose-Fermi systems consisting of a two-dimensional electron gas in the vicinity of an exciton condensate: We show that a pair-of-bogolons--mediated scattering proves to be dominating over the conventional acoustic phonon channel and over the single-bogolon scattering, even if the screening is taken into account. We develop a microscopic theory of this effect, focusing on GaAs and MoS$_2$ materials, and find the principal temperature dependence of resistivity, distinct from the conventional phonon--mediated processes. Further, we scrutinize parameters and suggest a way to design composite samples with predefined electron mobilities and propose a mechanism of electron pairing for superconductivity.

cond-mat.mes-hall↗

arXiv2016

Blackhole evaporation model without information loss

A simple model of a blackhole evaporation without information loss is given. In this model, the blackhole is \textit{not} in a specific mass eigenstate as it evaporates but rather, is in a superposition of various mass eigenstates and is entangled with the radiation. For astrophysical blackhole, the mass distribution is sharply peak about its average value with a vanishingly small standard deviation, which is consistent with our intuition of a classical object. It is then shown that as the blackhole evaporates, the evolution of the closed blackhole-radiation system is unitary. This is done by showing that the full density matrix satisfies Tr$ρ^2=1$ at all times. Finally, it is shown that the entanglement entropy, after an initial increase, decreases and approaches zero. These show that this model of blackhole evaporation has no infromation loss.

physics.gen-ph↗

arXiv2016

Relativistic Superfluids in Curved Spacetime

Superfluids under an intense gravitational field are typically found in compact stellar cores. Most treatments of these superfluids, however, are done using a flat spacetime background. In this paper, the effect of spacetime curvature on relativistic superfluids is investigated. The scalar-field superfluid in a background metric of a typical star core is considered first. It is found that the superfluid formed inside a compact object can not be of spherical shape. Explicit numerical calculation of the gravitational correction to the superfluid order parameter is performed for two specific examples with different boundary conditions. It is found that even in the weak-gravity limit, gravity can have a significant effect on superfluidity. The relativistic superfluids formed by various fermion pairings are also considered. Two possible cases are considered in the mean-field treatment: antifermion-fermion and fermion-fermion pairings. The effective actions and the self-consistent equations are derived for both cases. An analytical expression for the first-order gravitational correction to the superfluid order parameter is given for the antifermion-fermion pairing; while, the analytical expressions for the matrix elements of the heat kernel operator, which is useful in curved-spacetime QFT calculations, is derived for the fermion-fermion pairing.

astro-ph.SR↗