arXiv subjects

Esteban Marulanda

Publications and source records attributed to Esteban Marulanda.

7 recordsLinked to original sources

arXiv2026

Terahertz Lattice Imprint of a Hidden Multipolar Ordering Transition in Gd$_2$Ru$_2$O$_7$

Magnetic order carried by higher-rank multipoles produces no net moment and couples only weakly to conventional dipolar probes. Recently, the lattice has been proposed as an alternative detection channel for the associated ordering transitions. Here we report magneto-terahertz time-domain spectroscopy of the pyrochlore ruthenate Gd$_2$Ru$_2$O$_7$, in which a single spectrum resolves an exchange-split Gd$^{3+}$ transition and an infrared-active optical phonon. The temperature and field dependence of the magnetic mode give two independent determinations of the internal exchange field at the rare-earth site, which yield a magnitude of 5-6 T and a free-ion $g$-factor. The optical phonon, sensitive to spin-disorder scattering rather than to the static exchange field, exhibits a sharp anomaly in frequency and lifetime at 10 K that shifts to 30 K under 7 T, which we identify as an ordering transition of the Gd sublattice hidden from bulk thermodynamic probes. These results identify spin-phonon coupling as a route to rare-earth ordering transitions in multipolar magnets, one that is applicable to polycrystalline samples.

cond-mat.str-el↗

arXiv2026

Galilean boost invariance does not survive the trace: symmetry breaking in open quantum systems

Tracing out a Galilean-invariant Caldeira-Leggett environment breaks Galilean boost covariance of the reduced dynamics, while spatial translations and rotations survive intact. An operator-level analysis of the exact Hu-Paz-Zhang master equation localizes the violation entirely in the dissipative anticommutator term, scaling with the damping coefficient $Γ(t)f(t)$. The fluctuation-dissipation theorem ties this coefficient to the absorptive bath response that drives equilibrium momentum diffusion, so for any non-trivial bath spectral density bilinear-coupled Galilean invariance, the fluctuation-dissipation theorem, and reduced boost covariance cannot hold simultaneously. The stochastic decomposition of the influence functional extends the mechanism beyond the quadratic regime. The dimensionless ratio $\hbarγ/k_\mathrm{B} T$ delineates the crossover: cold atoms in dissipative optical lattices and ultracold molecules sit at its edge. Parametric driving offers a one-directional escape: the squeezing rate that protects nonequilibrium entanglement above the standard quantum limit also suppresses boost-breaking over a driving cycle.

quant-ph↗

arXiv2025

Windowing in terahertz time-domain spectroscopy: resolving resonances in thin-film samples

Terahertz time-domain spectroscopy (THz-TDS) has become a powerful tool for investigating the optical properties of thin films, offering direct access to the complex permittivity in the terahertz range. However, in transmission-based measurements of thin films on thick substrates, multiple reflections and limited time windows can introduce artifacts that obscure resonant features such as phonon modes. Time-domain windowing remains one of the most widely adopted strategies to mitigate these effects, yet systematic guidelines on its application remain scarce. In this work, we organize a practical routine for extracting the complex permittivity from THz-TDS data, focusing on when and how to apply time-domain windowing. The routine incorporates decision points for truncation versus smooth apodization, and emphasizes tailoring the window length and shape to specific signal conditions. We demonstrate the approach using representative measurements on PbTe thin films, highlighting cases in which truncation suffices, where apodization is essential, and how different window functions and lengths influence the resulting spectra. We also propose simple metrics to assess signal continuity and guide window selection. Although other analysis techniques exist, including parametric spectral estimation, this study focuses on formalizing windowing-based processing into an accessible experimental workflow. Our results show that the choice of window parameters can significantly affect the accuracy of extracted material parameters, particularly for sharply resonant systems. This work provides an accessible framework for improving spectral fidelity in THz-TDS of thin-film samples.

physics.optics↗

arXiv2023

Generalized Finite Differences Method Applied to Finite Photonic Crystal

We propose a Generalized Finite-Differences in the Frequency Domain method for the computation of photonic band structures of finite photonic crystals. Our approach is to discretize some fundamental domain instead of a single unit cell, such that boundary conditions of interest can be introduced into the eigenvalue problem. The validity and effectiveness of the proposed method are shown for the case of a one-dimensional photonic crystal embedded in an optical cavity. The limit from finite to infinite photonic crystals is reviewed in view of the proposed method.

physics.comp-ph↗

arXiv2023

Influence of Initial Entangled States on the Temperature-Dependent CHSH Inequality

We demonstrate that the temperature affects the validity of the CHSH inequality in an open bipartite two-qubit system. Specifically, for initial entangled states within the decoherence-free subspace (DFS), the CHSH inequality remains temperature-independent. In contrast, other entangled states exhibit a temperature threshold beyond which the inequality holds.

quant-ph↗

arXiv2023

Experimental parameters' Uncertainty limits for z-scan and f-scan techniques

In this paper, we present an analytical study of the relationship between the statistical distribution of a physical parameter and the uncertainties in the physical quantities used to determine it through indirect measurement. We investigate two possible methods for determining the physical quantity: linear regression and inversion of the equation in the parameter. Our analysis focuses on finding the limits of "small" uncertainties to guarantee a Gaussian distribution to the indirect physical quantity. Also, we introduce the "reliability cone" concept to describe the dependence of errors on the physical parameters uncertainties. We propose a new probability distribution for significant uncertainties and define the first three moments. We apply these methods to the z-scan and f-scan techniques, presenting the most sensitive parameters for the nonlinear two-photon absorption coefficient measurement. Finally, we implement our findings on experimental data of the two-photon absorption coefficient in CdSe.

physics.optics↗

arXiv2022

Correspondence Between the Energy Equipartition Theorem in Classical Mechanics and its Phase-Space Formulation in Quantum Mechanics

In classical physics there is a well-known theorem in which it is established that the energy per degree of freedom is the same. However, in quantum mechanics due to the non-commutativity of some pairs of observables and the possibility of having non-Markovian dynamics, the energy is not equally distributed. We propose a correspondence between what we know about the classical energy equipartition theorem and its possible counterpart in phase-space formulation in quantum mechanics based on the Wigner representation. Also, we show that in the high-temperature regime, the classical result is recovered.

quant-ph↗