arXiv subjects

Carlos Silva-Acuna

Publications and source records attributed to Carlos Silva-Acuna.

9 recordsLinked to original sources

arXiv2026

SAKE: Spectral Autodiff Kernel Expansion for Geometric Liouvillian Transport. A Differential-Geometric Framework for Response Transport in Quantum Dynamical Systems

We introduce the Spectral Autodiff Kernel Expansion (SAKE), a differentiable computational framework for transporting nonlinear spectroscopic response between neighboring quantum dynamical models. Rather than recomputing multidimensional spectra independently for each Hamiltonian or Liouvillian, SAKE constructs local transport expansions about a reference model by combining forward-mode automatic differentiation with Duhamel transport theory. Automatic differentiation generates first-, second-, and third-order derivatives of the parameter-dependent Liouvillian, which are assembled into a pathway transport operator that maps the nonlinear response of a reference model onto neighboring systems. The framework is validated for a four-level excitonic dimer possessing an $su(2)\times su(2)$ symmetry by comparing second- and third-order transported pathway operators with exact projected transport matrices obtained from direct calculations. The third-order expansion accurately reproduces the projected transport operator and its associated pathway mixing. Beyond providing an efficient computational strategy, the transport operator reveals how coherent and dissipative perturbations redistribute amplitude among double-sided Feynman pathways, exposing mechanistic information that is not directly apparent from the nonlinear spectrum. SAKE thereby establishes a differentiable computational framework for nonlinear spectroscopy that supports efficient local parameter exploration, sensitivity analysis, and future inverse-design applications.

quant-ph↗

arXiv2026

State--Generator Geometry of Open Quantum Systems: Compatibility and Covariant Transport

We develop a geometry for transporting stationary-state response across the control space of an open quantum system. A physical model is represented by the ordered pair of its stationary state and dynamical generator. Embedding these pairs in a common ambient space induces a metric, a response one-form, and a closed two-form on the control manifold. The ambient space admits a canonical complex structure that exchanges state and generator directions, but the Liouvillian null-state condition restricts physical models to a submanifold that need not preserve this structure. For an amplitude-damped optical Bloch model, the metric and response two-form are compatible at the single point $ω=0$ and $g/Γ=1/\sqrt{2}$; the physical manifold is non-Kähler elsewhere. The induced metric defines the Levi--Civita connection, geodesics, and parallel transport without requiring Kähler compatibility. We compute the connection by automatic differentiation through the stationary Liouvillian solve and recover the symbolic result to machine precision. A two-point calculation then shows that the resulting geodesic differs from linear interpolation in control space and follows a shorter path through the family of state--generator models. This geometry supplies the intrinsic derivative and transport structure needed to carry observable response, including multidimensional spectra, between admissible stationary models.

quant-ph↗

arXiv2025

Coherent Spectroscopic Probes of Topology: A Velocity-Gauge Perspective

We present a velocity-gauge formalism for computing nonlinear current response functions in periodic systems and apply it to the Su-Schrieffer-Heeger (SSH) model as a minimal topological testbed. By retaining the full minimal coupling Hamiltonian and avoiding the rotating wave approximation, we construct gauge-consistent expressions for the linear and third-order current susceptibilities using retarded Green's functions. Our results reveal how nonlinear optical spectra encode not only energy-level transitions but also interband phase coherence and topological winding. In the topological phase, the third-order response exhibits characteristic phase inversions and spectral asymmetries that are absent in the trivial phase. These features reflect geometric changes in the Bloch eigenstates and highlight the role of virtual pathways in shaping the nonlinear signal. Our framework offers a robust and extensible platform for modeling nonlinear light-matter interactions in topological materials beyond the dipole approximation and the standard Coulomb-gauge formulation in molecular spectroscopy.

physics.chem-ph↗

arXiv2025

Spectroscopic signatures of biexcitons: A case study in Ruddlesden-Popper lead-halides

Exciton-exciton interactions are fundamental to the light-emitting properties of semiconductors, influencing applications from lasers to quantum light sources. In this study, we investigate the spectroscopic signatures and binding energy of biexcitons in a metal halide two-dimensional Ruddlesden-Popper structure, which is known for hosting distinct excitonic resonances with unique lattice coupling. Using three spectroscopic techniques - photoluminescence (PL) and two variations of two-dimensional electronic spectroscopy (2DES) - we map coherent one-quantum and two-quantum correlations to gain deeper insight into the biexciton characteristics. While PL spectroscopy is hindered by spectral broadening and reabsorption, 2DES provides a more accurate characterization, revealing multiple biexciton states and uncovering a mixed biexciton species arising from exciton cross-coupling. These findings highlight the importance of advanced spectroscopic approaches in accurately determining biexciton binding energies and offer new perspectives on many-body interactions in exciton-polarons within layered perovskites.

cond-mat.mtrl-sci↗

arXiv2024

A quantum analog of Huygen's clock: noise-induced synchronization

We propose a quantum analogue of the Huygens clock, in which the phases of two spins achieve synchronization through their interaction with a shared environment. The environment functions analogously to the escapement mechanism in a mechanical clock, regulating the gear train and permitting the advancement of timing in discrete intervals. In our proposed model, the relative phase of the two spins become synchronized through interaction with a mutual, correlated, environment. We show that for a system of qubits, several arguments can be made that significantly reduce the cardinality of the set of allowed measurements and, hence, the complexity of the problem. We present a numerically efficient method to calculate the degree of quantumness that exists in the correlations of our final density matrix. This method also provides a tight upper bound for when the system is described by rank-3 and rank-4 density matrices.

quant-ph↗

arXiv2022

Concerning the stability of hybrid biexcitons in organic polymer aggregates

Frenkel excitons are the primary photoexcitations in organic semiconductors and are ultimately responsible for the optical properties of such materials. They are also predicted to form \emph{bound} exciton pairs, termed biexcitons, which are consequential intermediates in a wide range of photophysical processes. Generally, we think of bound states as arising from an attractive interaction. However, here we report on our recent theoretical analysis predicting the formation of stable biexciton states in a conjugated polymer material arising from both attractive and repulsive interactions. We show that in J-aggregate systems, JJ-biexcitons can arise from repulsive dipolar interactions with energies $E_{JJ}> 2E_J$ while in H-aggregates, HH-biexciton states $E_{HH} < 2E_H$ corresponding to attractive dipole exciton/exciton interactions. These predictions are corroborated by using ultrafast double-quantum coherence spectroscopy on a PBTTT material that exhibits both J- and H-like excitonic behavior.

cond-mat.mtrl-sci↗

arXiv2021

Formation of a highly ordered red phase in a MEH-PPV: polystyrene pseudogels

In this work, we demonstrate the formation of a "red-phase" poly[2-methoxy, 5-(2'- ethyl-hexoxy)-1,4-phenylene vinylene-PPV] (MEH-PPV) embedded into a host matrix of highly entangled ultra-high molecular weight polystyrene (MEH-PPV/UHMW PS pseudogel) that allows the simple processing of the MEH-PPV solutions. We processed a "red-phase" in the gel, the gel shows that the features what have beed demonstrated in the solution can be observed in the processable gel for optoelectronics applications. [Yamagata, Hajime, and Hestand, Nicholas J. and Spano, Frank C. and Kohler, Anna and Scharsich, Christina and Hoffmann, Sebastian T. and Bassler, Heinz, The Journal of Chemical Physics, 2013, 139, 114903]

cond-mat.mtrl-sci↗

arXiv2016

Probing polaron excitation spectra in organic semiconductors by photoinduced-absorption-detected two-dimensional coherent spectroscopy

We report a theoretical description and experimental implementation of a novel two-dimensional coherent excitation spectroscopy based on quasi-steady-state photoinduced absorption measurement of a long-lived nonlinear population. We have studied a semiconductor-polymer:fullerene-derivative distributed heterostructure by measuring the 2D excitation spectrum by means of photoluminescence, photocurrent and photoinduced absorption from metastable polaronic products. We conclude that the photoinduced absorption probe is a viable and valuable probe in this family of 2D coherent spectroscopies.

cond-mat.mtrl-sci↗

arXiv2016

Do ultrafast exciton-polaron decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells?

All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the two-dimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20\,fs or less.

cond-mat.mtrl-sci↗