Pegah Darvehi | Searcharxiv

arXiv2026

Three wave mixing vacuum squeezing generation in a SNAIL-based Traveling-Wave Parametric Amplifier with alternated flux polarity

Recent demonstrations of squeezing generation using Traveling Wave Parametric Amplifiers (TWPAs) have opened the way for the application of broadband microwave squeezing in quantum sensing, quantum-enhanced detection, and continuous-variable quantum information. Here we demonstrate vacuum squeezing generation via residual three-wave mixing (3WM) in a Josephson TWPA based on superconducting nonlinear asymmetric inductive elements (SNAILs) with alternated magnetic flux polarity. By investigating competition between four-wave mixing (4WM) and 3WM nonlinearities, we prove that vacuum squeezing generation via residual 3WM is possible when a careful choice of the operating flux point is adopted. Our study provides valuable insights on the impact of competing nonlinearities on TWPA squeezers, potentially extending the range of applications in the framework of microwave photonics.

quant-ph↗

arXiv2025

Impact of hydrogenation on the structure, chemistry, and electrical properties of flame-synthesized carbon nanoparticle films

The interaction between hydrogen atoms and carbon nanoparticles is a fundamental process governing the properties of carbonaceous materials in environments ranging from combustion systems to the interstellar medium. This study investigates the effects of controlled atomic hydrogen exposure on young and mature soot nanoparticles, generated in premixed ethylene-air flames, and deposited on substrates. We employed a multi-technique approach to characterize the chemical, mechanical, and electrical evolution of the films. In-situ infrared spectroscopy revealed non-monotonic behavior: an initial increase in aliphatic CH bonds was observed, followed by a decrease at higher hydrogen fluences. This was accompanied by a continuous decrease in the aromatic C=C signal. Atomic force microscopy showed a significant increase in the Young's modulus of the film for both sample types after hydrogenation. This mechanical change was correlated with an increase in the I(D)/I(G) ratio from Raman spectroscopy. Furthermore, both macroscopic current vs. voltage and local scanning tunneling spectroscopy measurements demonstrated a notable increase in electrical conductivity. For single just-formed soot particles, moreover, a hydrogen-induced transformation from a semiconductive to a semi-metallic nature was observed. The collective evidence points towards an H-induced CC cross-linking mechanism within the nanoparticle films. We propose that atomic hydrogen facilitates the formation of radical sites, which promotes covalent bond formation between adjacent particles or molecular units, creating a more interconnected and rigid network, with smaller interlayer distance. These findings provide crucial insights into the structural evolution of carbonaceous materials in hydrogen-rich environments, with direct implications for understanding soot formation and for the tailored design of carbon-based materials.

cond-mat.mes-hall↗

arXiv2023

Engineering monstar polarization disclination through geometric phase

We present a method to generate monstar singularities via Pancharatnam-Berry phase by the coherent collinear superposition of two Free-Form Dark Hollow beams, $FFDH^{m}_{q}$, of topological charge $q$, and order of symmetry $m$. FFDH beams are generated with the geometrical parameters of a closed curve exploited to obtain a nonuniform rotation rate of the local polarization azimuth and generate monstar patterns. We report space-variant polarization patterns: radial- and azimuthal-like, lemon- and star-like for symmetric disclinations, and the asymmetric monstar disclination. We present theory and measurements, and find excellent agreement between the two.

physics.optics↗