Showing 1–50 of 71 results for author: Marini, A

The On-Sky Performance of the LSST Camera CCD Array

Authors: Sean Patrick MacBride, Aaron Roodman, Stuart Marshall, Yousuke Utsumi, Kevin Fanning, John Banovetz, Theo Schutt, Alexander Broughton, Shuang Liang, Andrew P. Rasmussen, Pierre Antilogus, John Gregg Thayer, Homer Neal, Anthony S. Johnson, Pierre Astier, Seth W. Digel, Andrew Bradshaw, Johan Bregeon, James Chiang, Céline Combet, Guillaume Dargaud, Johnny H. Esteves, Marcelle Soares-Santos, Thibault Guillemin, Claire Juramy-Gilles , et al. (67 additional authors not shown)

Abstract: The focal plane of the LSST Camera contains 189 individual science CCDs, arranged into 21 raft tower modules, along with 4 wavefront and 8 guider CCDs located in 4 additional corner RTMs. Altogether, the LSST Camera CCDs compose the largest focal plane ever constructed. The LSST Camera is the primary instrument of Rubin Observatory, which will begin the Legacy Survey of Space and Time in 2026. In… ▽ More The focal plane of the LSST Camera contains 189 individual science CCDs, arranged into 21 raft tower modules, along with 4 wavefront and 8 guider CCDs located in 4 additional corner RTMs. Altogether, the LSST Camera CCDs compose the largest focal plane ever constructed. The LSST Camera is the primary instrument of Rubin Observatory, which will begin the Legacy Survey of Space and Time in 2026. In this paper, we describe the on-sky performance of the LSST Camera CCDs, from receipt at NSF/DOE Vera C. Rubin Observatory in May 2024 to on-sky observations during the first year of operations. We discuss the process to establish functionality of several CCDs which were affected by an electrical short and faulty analog-digital converter, optimizations of readout timing in response to changes in the survey strategy, and implementation of enhanced focal plane safety measures through an active clearing mechanism on the CCDs. Finally, we discuss sensor features observed on-sky, and global performance during the first year of operations. The operations to date of the LSST Camera CCDs have demonstrated the capability of performing a wide, fast, and deep optical imaging survey of the entire southern sky at the Rubin Observatory. △ Less

Submitted 30 June, 2026; originally announced June 2026.

Comments: 21 pages, 8 figures, 2 tables, submitted to SPIE Ground-based and Airborne Telescopes XI 14157

Enantio-selective inverse Faraday effect in isotropic chiral molecular mixtures

Authors: Raju Adhikary, Ambaresh Sahoo, Matteo Silvestri, Massimiliano Aschi, Antonio Mecozzi, Davide Tedeschi, Carino Ferrante, Andrea Marini

Abstract: Enantiomeric excess detection in a chiral molecular mixture is paramount because very often opposite enantiomers exhibit profound functional dissimilarities that play decisive roles in biochemical applications. Existing chiral sensing methods mostly rely on large operational sample volumes, hindering compatibility with integrated sensing schemes. Here, we propose a novel chiroptical sensing techni… ▽ More Enantiomeric excess detection in a chiral molecular mixture is paramount because very often opposite enantiomers exhibit profound functional dissimilarities that play decisive roles in biochemical applications. Existing chiral sensing methods mostly rely on large operational sample volumes, hindering compatibility with integrated sensing schemes. Here, we propose a novel chiroptical sensing technique based on the inverse Faraday effect in a photonic micro-capillary filled with nl-volume chiral drug solution. We theoretically demonstrate that, upon excitation by intense laser light, an isotropic assembly of chiral drugs produces a static magnetisation, with amplitude and direction depending on the enantiomeric excess. In turn, by measuring the chirally-sensitive static magnetic field in the vicinity of the micro-tube one can retrieve the enantiomeric excess of the chiral drug solution. Our theoretical predictions unlock new opportunities for the development of innovative nanophotonic devices suitable for efficient chiroptical sensing with nl-volume sensitivity. △ Less

Submitted 14 June, 2026; originally announced June 2026.

Scaling native entanglement generation in layered semiconductors with quasi-phase matching

Authors: Benjamin Braun, Andrea Alessandrini, Josip Bajo, Philipp K. Jenke, Leone di Mauro Villari, Birui Yang, Zhi Hao Peng, P. James Schuck, Cory R. Dean, Andrea Marini, Philip Walther, Chiara Trovatello, Lee A. Rozema

Abstract: Efficient generation of entangled photons typically relies on spontaneous parametric down-conversion (SPDC) in phase-matched macroscopic nonlinear media. However, generating entanglement under phase-matching constraints requires additional bulk optics or interferometers. In contrast, ultrathin van der Waals semiconductors - such as transition metal dichalcogenides (TMDs) - exhibit strong enough op… ▽ More Efficient generation of entangled photons typically relies on spontaneous parametric down-conversion (SPDC) in phase-matched macroscopic nonlinear media. However, generating entanglement under phase-matching constraints requires additional bulk optics or interferometers. In contrast, ultrathin van der Waals semiconductors - such as transition metal dichalcogenides (TMDs) - exhibit strong enough optical nonlinearities for SPDC to be observed from subwavelength-thick media, thereby bypassing conventional phase-matching constraints. In this microscopic domain, the intrinsic crystal symmetry governs the nonlinear optical response, enabling the native generation of polarization-entangled photon pairs. However, generating these states efficiently has been fundamentally restricted by the material's coherence length ($L_c$), which limits the attainable conversion efficiency. Here, we investigate periodically-poled TMDs (PPTMDs) designed to scale up this interaction via quasi-phase matching. We demonstrate that mechanically flipping the sign of the nonlinearity at precise intervals of $L_c$ introduces quasi-phase matching, that scales the pair-production rate while preserving the pristine, symmetry-generated polarization entanglement, with fidelities exceeding 99%. Backed by a rigorous theoretical model, our work clarifies the interplay between crystal symmetry and propagation effects in thin nonlinear media, providing a new avenue for engineering quantum light in nanophotonic systems. △ Less

Submitted 12 June, 2026; originally announced June 2026.

Comments: 7 pages, 3 figures, and an Appendix

Chirally-sensitive optical rectification by isotropic chiral media

Authors: Raju Adhikary, Luca Assogna, Ambaresh Sahoo, Matteo Venturi, Andrea De Marcellis, Massimiliano Aschi, Antonio Mecozzi, Jens Biegert, Davide Tedeschi, Carino Ferrante, Andrea Marini

Abstract: Chiroptical sensing is central to gain fundamental insight into electronic, vibrational and rotational degrees of freedom of chiral molecules, and is a cornerstone for nanomedicine and drug discovery platforms. Current chiral sensing technologies to assess the enantiomeric imbalance of chiral pharmaceutical compounds are sensitive to ml volumes but are time-consuming and cannot be integrated on a… ▽ More Chiroptical sensing is central to gain fundamental insight into electronic, vibrational and rotational degrees of freedom of chiral molecules, and is a cornerstone for nanomedicine and drug discovery platforms. Current chiral sensing technologies to assess the enantiomeric imbalance of chiral pharmaceutical compounds are sensitive to ml volumes but are time-consuming and cannot be integrated on a chip, thus creating a major bottleneck for drug discovery and nanomedicine. Here, we propose a novel chiroptical sensing approach based on optical rectification in a photonic micro-cavity filled by a drug solution with nl volume. We theoretically demonstrate that, upon optical excitation by intense pulsed laser light, such a nonlinear effect produces a chirally-sensitive nV voltage burst at the electrically-gated micro-cavity boundaries, with sign depending solely on the drug enantiomeric imbalance. Our results shed light on the potential of optical rectification as a robust platform for innovative lab-on-a-chip devices enabling chiral sensing with nl sensitivity. △ Less

Submitted 12 June, 2026; originally announced June 2026.

Development and integration of the NA64-DTC automation controller for the CERN "DESY Table" motorized platform

Authors: A. Antonov, A. Celentano, A. Marini, L. Marsicano

Abstract: We report on the development, construction, and integration of a remote automation controller \texttt{NA64-DTC} for the so-called ``DESY Table'' motorised platform widely used at CERN East-Area and North-Area experimental installations. The device is based on an ESP32-C3 System-on-Module that interfaces with the table manual control panel via a signal duplication connector. Button presses are emul… ▽ More We report on the development, construction, and integration of a remote automation controller \texttt{NA64-DTC} for the so-called ``DESY Table'' motorised platform widely used at CERN East-Area and North-Area experimental installations. The device is based on an ESP32-C3 System-on-Module that interfaces with the table manual control panel via a signal duplication connector. Button presses are emulated through opto-isolated switches, to allow for simultaneous operation with the manual system without modifying the original hardware. A \texttt{HTTP} server running on the controller allows interfacing with the device, enabling experiment-specific integration solutions. \\ The device was successfully commissioned at CERN, exploiting the experimental installations at PS-T9 and SPS-H4 beamlines. This work describes in detail the device technical design and operation, as well as the performance obtained during the commissioning operations. Although initially conceived for the NA64 experiment, the proposed solution can be of interest to all CERN experiments making use of the DESY Table platform, enabling remote and automated operation while reducing manual intervention during beam activities. △ Less

Submitted 9 August, 2026; v1 submitted 1 June, 2026; originally announced June 2026.

Comments: Version accepted for publication on "Instruments" journal

Enhanced third harmonic response of the PtTe$_2$ transition metal dichalcogenide

Authors: Leone Di Mauro Villari, Simone Grillo, Olivia Pulci, Salvatore Macis, Stefano Lupi, Andrea Marini

Abstract: We investigate the third harmonic response of platinum ditelluride (PtTe$_2$), a Dirac semimetal belonging to the transition metal dichalcogenides class. Due to its topological properties, this material has drawn a lot of attention, particularly because it hosts type-II (super-critically tilted) Dirac fermions in the $\rm A-Γ-\rm A$ high symmetry direction. Adopting a low-energy model fitted direc… ▽ More We investigate the third harmonic response of platinum ditelluride (PtTe$_2$), a Dirac semimetal belonging to the transition metal dichalcogenides class. Due to its topological properties, this material has drawn a lot of attention, particularly because it hosts type-II (super-critically tilted) Dirac fermions in the $\rm A-Γ-\rm A$ high symmetry direction. Adopting a low-energy model fitted directly from density functional theory band structure simulations, we calculate analytically the nonlinear conductivity. We observe that third-order optical nonlinearities are efficiently modulated by the cones tilting, which produces a significant enhancement of the nonlinear susceptibility. Our results, besides shedding light on topological transitions of platinum ditelluride, are relevant for future nanophotonic devices exploiting the tunable nonlinear properties of type-II Dirac fermions. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Design and characterization of the POKERINO prototype for the POKER/NA64 experiment at CERN

Authors: Andrei Antonov, Pietro Bisio, Mariangela Bondì, Andrea Celentano, Anna Marini, Luca Marsicano

Abstract: The NA64 experiment at CERN H4 beamline recently started a high-energy positron-beam program to search for light dark matter particles through a thick-target, missing-energy measurement. To fulfil the energy resolution requirement of the physics measurement $σ_E/E\simeq2.5\%/\sqrt{E\mathrm{[GeV}]} \oplus 0.5\%$ and cope with the constraints and performance requests of the NA64 setup, a new high-re… ▽ More The NA64 experiment at CERN H4 beamline recently started a high-energy positron-beam program to search for light dark matter particles through a thick-target, missing-energy measurement. To fulfil the energy resolution requirement of the physics measurement $σ_E/E\simeq2.5\%/\sqrt{E\mathrm{[GeV}]} \oplus 0.5\%$ and cope with the constraints and performance requests of the NA64 setup, a new high-resolution homogeneous electromagnetic calorimeter PKR-CAL has been designed. The detector is based on PbWO$_4$ crystals, each read by multiple SiPM sensors to maximize the light collection. The PKR-CAL design has been optimized to mitigate and control unavoidable SiPM saturation effects at high light levels, as well as to minimize the gain fluctuations induced by instantaneous variations of the H4 beam intensity. The $R\&D$ program culminated in the construction of a small-scale prototype, POKERINO. In this work, we present the results from the experimental characterization campaign of the POKERINO aiming at demonstrating that the obtained performances are compatible with the application requirements. △ Less

Submitted 21 March, 2026; v1 submitted 23 January, 2026; originally announced January 2026.

Femtosecond self-diffraction as a measure of the nonlinear response spectrum

Authors: Luca Assogna, Giovanna Salvitti, Matteo Silvestri, Federico Perrella, Riccardo Mincigrucci, Cristian Soncini, Elena Incerto, Armando Carlone, Majed Chergui, Claudio Masciovecchio, Paola Benassi, Andrea Marini, Davide Tedeschi, Carino Ferrante

Abstract: Self diffraction is a four-wave mixing process proportional to the square modulus of third-order nonlinearity susceptibility $χ^{(3)}$, which is related to the material's electronic and thermal properties. In this study, we investigate the wavelength dependence of the self-diffracted signal generated by a femtosecond pulsed laser in a dye solution to directly evaluate the electronic third-order no… ▽ More Self diffraction is a four-wave mixing process proportional to the square modulus of third-order nonlinearity susceptibility $χ^{(3)}$, which is related to the material's electronic and thermal properties. In this study, we investigate the wavelength dependence of the self-diffracted signal generated by a femtosecond pulsed laser in a dye solution to directly evaluate the electronic third-order nonlinear susceptibility spectrum. By accounting for absorption effects and phase matching conditions, we determine the $\vertχ^{(3)}\vert$ for different concentrations. Experimental results complemented with theoretical predictions, show that in the low absorption and thin sample limits, the signal reproduce the $\vertχ^{(3)}\vert$ spectral profile. These findings demonstrate the feasibility of measuring nonlinear susceptibility spectra arising solely from the bound-electronic response across a wide spectral range and for various compounds. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Enhanced vibrational optical activity by near-zero index chiral effective media

Authors: Ashis Paul, Matteo Venturi, Raju Adhikary, Giovanna Salvitti, Andrea Toma, Francesco Di Stasio, Hatice Altug, Paola Benassi, Davide Tedeschi, Carino Ferrante, Andrea Marini

Abstract: The enhancement of the inherently weak optical activity of solvated molecules by superchiral fields, crucial for detecting their chirality, is a research frontier of photonics and the basis of novel chiroptical detection schemes. Here, we show that an effective medium consisting of randomly dispersed metal-based nanoparticles embedded within an optically active solvated drug (aqueous reparixin) ca… ▽ More The enhancement of the inherently weak optical activity of solvated molecules by superchiral fields, crucial for detecting their chirality, is a research frontier of photonics and the basis of novel chiroptical detection schemes. Here, we show that an effective medium consisting of randomly dispersed metal-based nanoparticles embedded within an optically active solvated drug (aqueous reparixin) can enhance vibrational optical rotation and circular dichroism thanks to superchirality produced by slow light in near-zero index conditions. We evaluate from first principles the effective bianisotropic response of the bulk chiral effective medium, showing that, by adjusting the nanoparticles filling fraction, vibrational optical activity is greatly enhanced by a factor $\simeq 10^2-10^3$ at the near-zero index resonance. Our results are relevant for the development of innovative devices capable of detecting the chirality of low-volume samples, with applications in quantum chemistry and nanomedicine. △ Less

Submitted 18 June, 2025; originally announced June 2025.

Technical report on a quantum-inspired solver for simulating compressible flows

Authors: Raghavendra Dheeraj Peddinti, Stefano Pisoni, Egor Tiunov, Alessandro Marini, Leandro Aolita

Abstract: This document presents a quantum-inspired solver for 2D Euler equations, accepted at the final phase of the Airbus-BWM Group Quantum Computing Challenge (ABQCC) 2024. We tackle the case study of Quantum Solvers for Predictive Aeroacoustic and Aerodynamic modeling tasks. We propose a tensor network based solver that scales polylogarithmically with the mesh size, in both runtime and memory. This pro… ▽ More This document presents a quantum-inspired solver for 2D Euler equations, accepted at the final phase of the Airbus-BWM Group Quantum Computing Challenge (ABQCC) 2024. We tackle the case study of Quantum Solvers for Predictive Aeroacoustic and Aerodynamic modeling tasks. We propose a tensor network based solver that scales polylogarithmically with the mesh size, in both runtime and memory. This provides a promising avenue for tackling the curse of dimensionality that plagues the direct numerical simulations in the field of computational fluid dynamics. △ Less

Submitted 4 June, 2025; originally announced June 2025.

High efficiency veto hadron calorimeter in the NA64 experiment at CERN

Authors: Yu. M. Andreev, A. Antonov, M. A. Ayala Torres, D. Banerjee, B. Banto Oberhauser, V. Bautin, J. Bernhard, P. Bisio, M. Bondì, A. Celentano, N. Charitonidis, P. Crivelli, A. V. Dermenev, S. V. Donskov, R. R. Dusaev, T. Enik, V. N. Frolov, S. V. Gertsenberger, S. Girod, S. N. Gninenko, M. Hösgen, Y. Kambar, A. E. Karneyeu, G. Kekelidze, B. Ketzer , et al. (31 additional authors not shown)

Abstract: NA64 is a fixed-target experiment at the CERN SPS designed to search for Light particle Dark Matter (LDM) candidates with masses in the sub-GeV range. During the 2016-2022 runs, the experiment obtained the world-leading constraints, leaving however part of the well-motivated region of parameter space suggested by benchmark LDM models still unexplored. To further improve sensitivity, as part of the… ▽ More NA64 is a fixed-target experiment at the CERN SPS designed to search for Light particle Dark Matter (LDM) candidates with masses in the sub-GeV range. During the 2016-2022 runs, the experiment obtained the world-leading constraints, leaving however part of the well-motivated region of parameter space suggested by benchmark LDM models still unexplored. To further improve sensitivity, as part of the upgrades to the setup of NA64 at the CERN SPS H4 beamline, a prototype veto hadron calorimeter (VHCAL) was installed in the downstream region of the experiment during the 2023 run. The VHCAL, made of Cu-Sc layers, was expected to be an efficient veto against upstream electroproduction of large-angle hadrons or photon-nuclear interactions, reducing the background from secondary particles escaping the detector acceptance. With the collected statistics of $4.4\times10^{11}$ electrons on target (EOT), we demonstrate the effectiveness of this approach by rejecting this background by more than an order of magnitude. This result provides an essential input for designing a full-scale optimized VHCAL to continue running background-free during LHC Run 4, when we expect to collect $10^{13}$ EOT. Furthermore, this technique combined with improvements in the analysis enables us to decrease our missing energy threshold from 50 GeV to 40 GeV thereby enhancing the signal sensitivity of NA64. △ Less

Submitted 28 March, 2025; v1 submitted 14 March, 2025; originally announced March 2025.

Comments: 13 pages, 12 figures

Report number: CERN-EP-2025-04

Proof of principle for a light dark matter search with low-energy positron beams at NA64

Authors: Yu. M. Andreev, A. Antonov, M. A. Ayala Torres, D. Banerjee, B. Banto Oberhauser, V. Bautin, J. Bernhard, P. Bisio, M. Bondì, A. Celentano, N. Charitonidis, P. Crivelli, A. V. Dermenev, S. V. Donskov, R. R. Dusaev, T. Enik, V. N. Frolov, S. V. Gertsenberger, S. Girod, S. N. Gninenko, M. Hösgen, Y. Kambar, A. E. Karneyeu, G. Kekelidze, B. Ketzer , et al. (32 additional authors not shown)

Abstract: Thermal light dark matter (LDM) with particle masses in the 1 MeV - 1 GeV range could successfully explain the observed dark matter abundance as a relic from the primordial Universe. In this picture, a new feeble interaction acts as a "portal" between the Standard Model and LDM particles, allowing for the exploration of this paradigm at accelerator experiments. In the last years, the "missing ener… ▽ More Thermal light dark matter (LDM) with particle masses in the 1 MeV - 1 GeV range could successfully explain the observed dark matter abundance as a relic from the primordial Universe. In this picture, a new feeble interaction acts as a "portal" between the Standard Model and LDM particles, allowing for the exploration of this paradigm at accelerator experiments. In the last years, the "missing energy" experiment NA64e at CERN SPS (Super Proton Synchrotron) has set world-leading constraints in the vector-mediated LDM parameter space, by exploiting a 100 GeV electron beam impinging on an electromagnetic calorimeter, acting as an active target. In this paper, we report a detailed description of the analysis of a preliminary measurement with a 70 GeV positron beam at NA64e, performed during summer 2023 with an accumulated statistic of 1.6 x 10^10 positrons on target. This data set was analyzed with the primary aim of evaluating the performance of the NA64e detector with a lower energy positron beam, towards the realization of the post-LS3 program. The analysis results, other than additionally probing unexplored regions in the LDM parameter space, provide valuable information towards the future NA64e positron campaign. △ Less

Submitted 28 May, 2025; v1 submitted 6 February, 2025; originally announced February 2025.

A new hybrid gadolinium nanoparticles-loaded polymeric material for neutron detection in rare event searches

Authors: DarkSide-20k Collaboration, :, F. Acerbi, P. Adhikari, P. Agnes, I. Ahmad, S. Albergo, I. F. Albuquerque, T. Alexander, A. K. Alton, P. Amaudruz, M. Angiolilli, E. Aprile, R. Ardito, M. Atzori Corona, D. J. Auty, M. Ave, I. C. Avetisov, O. Azzolini, H. O. Back, Z. Balmforth, A. Barrado Olmedo, P. Barrillon, G. Batignani, P. Bhowmick , et al. (290 additional authors not shown)

Abstract: Experiments aimed at direct searches for WIMP dark matter require highly effective reduction of backgrounds and control of any residual radioactive contamination. In particular, neutrons interacting with atomic nuclei represent an important class of backgrounds due to the expected similarity of a WIMP-nucleon interaction, so that such experiments often feature a dedicated neutron detector surround… ▽ More Experiments aimed at direct searches for WIMP dark matter require highly effective reduction of backgrounds and control of any residual radioactive contamination. In particular, neutrons interacting with atomic nuclei represent an important class of backgrounds due to the expected similarity of a WIMP-nucleon interaction, so that such experiments often feature a dedicated neutron detector surrounding the active target volume. In the context of the development of DarkSide-20k detector at INFN Gran Sasso National Laboratory (LNGS), several R&D projects were conceived and developed for the creation of a new hybrid material rich in both hydrogen and gadolinium nuclei to be employed as an essential element of the neutron detector. Thanks to its very high cross-section for neutron capture, gadolinium is one of the most widely used elements in neutron detectors, while the hydrogen-rich material is instrumental in efficiently moderating the neutrons. In this paper results from one of the R&Ds are presented. In this effort the new hybrid material was obtained as a poly(methyl methacrylate) (PMMA) matrix, loaded with gadolinium oxide in the form of nanoparticles. We describe its realization, including all phases of design, purification, construction, characterization, and determination of mechanical properties of the new material. △ Less

Submitted 29 April, 2024; originally announced April 2024.

Journal ref: JINST 19 P09021 (2024)

Quasi-phase-matched up- and down-conversion in periodically poled layered semiconductors

Authors: Chiara Trovatello, Carino Ferrante, Birui Yang, Josip Bajo, Benjamin Braun, Xinyi Xu, Zhi Hao Peng, Philipp K. Jenke, Andrew Ye, Milan Delor, D. N. Basov, Jiwoong Park, Philip Walther, Lee A. Rozema, Cory Dean, Andrea Marini, Giulio Cerullo, P. James Schuck

Abstract: Nonlinear optics lies at the heart of classical and quantum light generation. The invention of periodic poling revolutionized nonlinear optics and its commercial applications by enabling robust quasi-phase-matching in crystals such as lithium niobate. However, reaching useful frequency conversion efficiencies requires macroscopic dimensions, limiting further technology development and integration.… ▽ More Nonlinear optics lies at the heart of classical and quantum light generation. The invention of periodic poling revolutionized nonlinear optics and its commercial applications by enabling robust quasi-phase-matching in crystals such as lithium niobate. However, reaching useful frequency conversion efficiencies requires macroscopic dimensions, limiting further technology development and integration. Here we realize a periodically poled van der Waals semiconductor (3R-MoS$_2$). Due to its exceptional nonlinearity, we achieve macroscopic frequency conversion efficiency of 0.03% at the relevant telecom wavelength over a microscopic thickness of 3.4$μ$m (that is, 3 poling periods), $10-100\times$ thinner than current systems with similar performances. Due to unique intrinsic cavity effects, the thickness-dependent quasi-phase-matched second harmonic signal surpasses the usual quadratic enhancement by $50\%$. Further, we report the broadband generation of photon pairs at telecom wavelengths via quasi-phase-matched spontaneous parametric down-conversion, showing a maximum coincidence-to-accidental-ratio of $638 \pm 75$. This work opens the new and unexplored field of phase-matched nonlinear optics with microscopic van der Waals crystals, unlocking applications that require simple, ultra-compact technologies such as on-chip entangled photon-pair sources for integrated quantum circuitry and sensing. △ Less

Submitted 11 February, 2025; v1 submitted 8 December, 2023; originally announced December 2023.

Complete quantum-inspired framework for computational fluid dynamics

Authors: Raghavendra D. Peddinti, Stefano Pisoni, Alessandro Marini, Philippe Lott, Henrique Argentieri, Egor Tiunov, Leandro Aolita

Abstract: Computational fluid dynamics is both a thriving research field and a key tool for advanced industry applications. The central challenge is to simulate turbulent flows in complex geometries, a compute-power intensive task due to the large vector dimensions required by discretized meshes. We present a full-stack method to solve for incompressible fluids with memory and runtime scaling poly-logarithm… ▽ More Computational fluid dynamics is both a thriving research field and a key tool for advanced industry applications. The central challenge is to simulate turbulent flows in complex geometries, a compute-power intensive task due to the large vector dimensions required by discretized meshes. We present a full-stack method to solve for incompressible fluids with memory and runtime scaling poly-logarithmically in the mesh size. Our framework is based on matrix-product states, a powerful compressed representation of quantum states. It is complete in that it solves for flows around immersed objects of arbitrary geometries, with non-trivial boundary conditions, and self-consistent in that it can retrieve the solution directly from the compressed encoding, i.e. without ever passing through the expensive dense-vector representation. This machinery lays the foundations for a new generation of potentially radically more efficient solvers of real-life fluid problems. △ Less

Submitted 22 September, 2023; v1 submitted 2 August, 2023; originally announced August 2023.

Plasmon-enhanced circular dichroism spectroscopy of chiral drug solutions

Authors: Matteo Venturi, Raju Adhikary, Ambaresh Sahoo, Carino Ferrante, Isabella Daidone, Francesco Di Stasio, Andrea Toma, Francesco Tani, Hatice Altug, Antonio Mecozzi, Massimiliano Aschi, Andrea Marini

Abstract: We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations.… ▽ More We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations. Furthermore, the subwavelength confinement of surface plasmon polaritons is key to attain chiroptical sensitivity to small amounts of drug volumes placed around $\simeq 100$ nm by the metal surface. Our calculations focus on reparixin, a pharmaceutical molecule currently used in clinical studies for patients with community-acquired pneumonia, including COVID-19 and acute respiratory distress syndrome. Considering realistic dilute solutions of reparixin dissolved in water with concentration $\leq 5$ mg$/$ml, we find a circular-dichroism differential absorption enhancement factor of the order $\simeq 20$ and chirality-induced polarization distortion upon surface plasmon polariton excitation. △ Less

Submitted 27 September, 2023; v1 submitted 16 August, 2023; originally announced August 2023.

Directionality of nuclear recoils in a liquid argon time projection chamber

Authors: The DarkSide-20k Collaboration, :, P. Agnes, I. Ahmad, S. Albergo, I. F. M. Albuquerque, T. Alexander, A. K. Alton, P. Amaudruz, M. Atzori Corona, M. Ave, I. Ch. Avetisov, O. Azzolini, H. O. Back, Z. Balmforth, A. Barrado-Olmedo, P. Barrillon, A. Basco, G. Batignani, V. Bocci, W. M. Bonivento, B. Bottino, M. G. Boulay, J. Busto, M. Cadeddu , et al. (243 additional authors not shown)

Abstract: The direct search for dark matter in the form of weakly interacting massive particles (WIMP) is performed by detecting nuclear recoils (NR) produced in a target material from the WIMP elastic scattering. A promising experimental strategy for direct dark matter search employs argon dual-phase time projection chambers (TPC). One of the advantages of the TPC is the capability to detect both the scint… ▽ More The direct search for dark matter in the form of weakly interacting massive particles (WIMP) is performed by detecting nuclear recoils (NR) produced in a target material from the WIMP elastic scattering. A promising experimental strategy for direct dark matter search employs argon dual-phase time projection chambers (TPC). One of the advantages of the TPC is the capability to detect both the scintillation and charge signals produced by NRs. Furthermore, the existence of a drift electric field in the TPC breaks the rotational symmetry: the angle between the drift field and the momentum of the recoiling nucleus can potentially affect the charge recombination probability in liquid argon and then the relative balance between the two signal channels. This fact could make the detector sensitive to the directionality of the WIMP-induced signal, enabling unmistakable annual and daily modulation signatures for future searches aiming for discovery. The Recoil Directionality (ReD) experiment was designed to probe for such directional sensitivity. The TPC of ReD was irradiated with neutrons at the INFN Laboratori Nazionali del Sud, and data were taken with 72 keV NRs of known recoil directions. The direction-dependent liquid argon charge recombination model by Cataudella et al. was adopted and a likelihood statistical analysis was performed, which gave no indications of significant dependence of the detector response to the recoil direction. The aspect ratio R of the initial ionization cloud is estimated to be 1.037 +/- 0.027 and the upper limit is R < 1.072 with 90% confidence level △ Less

Submitted 28 July, 2023; originally announced July 2023.

Comments: 20 pages, 10 figures, submitted to Eur. Phys. J. C

Journal ref: Eur. Phys. J. C 84:24 (2024)

Measurement of the intrinsic hadronic contamination in the NA64$-e$ high-purity $e^+/e^-$ beam at CERN

Authors: Yu. M. Andreev, D. Banerjee, B. Banto Oberhauser, J. Bernhard, P. Bisio, M. Bondi, A. Celentano, N. Charitonidis, A. G. Chumakov, D. Cooke, P. Crivelli, E. Depero, A. V. Dermenev, S. V. Donskov, R. R. Dusaev, T. Enik, V. N. Frolov, A. Gardikiotis, S. G. Gerassimov, S. N. Gninenko, M. H"osgen, M. Jeckel, V. A. Kachanov, Y. Kambar, A. E. Karneyeu , et al. (43 additional authors not shown)

Abstract: In this study, we present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c momentum. The analysis was performed using data collected by the NA64-$e$ experiment in 2022. Our study is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64-E… ▽ More In this study, we present the measurement of the intrinsic hadronic contamination at the CERN SPS H4 beamline configured to transport electrons and positrons at 100 GeV/c momentum. The analysis was performed using data collected by the NA64-$e$ experiment in 2022. Our study is based on calorimetric measurements, exploiting the different interaction mechanisms of electrons and hadrons in the NA64-ECAL and NA64-HCAL detectors. We determined the intrinsic hadronic contamination by comparing the results obtained using the nominal electron/positron beamline configuration with those obtained in a dedicated setup, in which only hadrons impinged on the detector. The significant differences in the experimental signatures of electrons and hadrons motivated our approach, resulting in a small and well-controlled systematic uncertainty for the measurement. Our study allowed us to precisely determine the intrinsic hadronic contamination, which represents a crucial parameter for the NA64 experiment in which the hadron contaminants may result in non-trivial backgrounds. Moreover, we performed dedicated Monte Carlo simulations for the hadron production induced by the primary T2 target. We found a good agreement between measurements and simulation results, confirming the validity of the applied methodology and our evaluation of the intrinsic hadronic contamination. △ Less

Submitted 11 October, 2023; v1 submitted 30 May, 2023; originally announced May 2023.

Report number: CERN-EP-2023-108

XUV plasmonic waveguides by near-zero index heterostructures

Authors: Luca Assogna, Carino Ferrante, Alessandro Ciattoni, Andrea Marini

Abstract: The lack of transmissive photonic components in the extreme ultra-violet (XUV) constitutes a challenge for micro/nano-metric confinement. Here, we theoretically design a novel approach to attain XUV radiation guidance based on the electromagnetic properties of Titanium-Aluminum-Titanium heterostructures in such a spectral domain. We show that, thanks to the near-zero-index properties of aluminum a… ▽ More The lack of transmissive photonic components in the extreme ultra-violet (XUV) constitutes a challenge for micro/nano-metric confinement. Here, we theoretically design a novel approach to attain XUV radiation guidance based on the electromagnetic properties of Titanium-Aluminum-Titanium heterostructures in such a spectral domain. We show that, thanks to the near-zero-index properties of aluminum and titanium, XUV radiation can couple efficiently with plasma oscillations in such heterostructures, enabling the excitation of several distinct plasmon polariton modes. Our predictions, based on the semi-analytical solution of fully vectorial Maxwell's equations, indicate that the dispersion profile of plasmon polariton modes can get efficiently modulated by the aluminum thickness, enabling nanometre confinement and micrometre propagation length. Moreover, we quantify the third-order nonlinearity enhancement factor, finding that it is resonant at the zero-index wavelength. Our results are promising for the development of future devices enabling advanced control and manipulation of XUV radiation. △ Less

Submitted 6 April, 2023; originally announced April 2023.

Characterization of the performances of plastic commercial scintillators in cryogenic environments

Authors: M. Biassoni, A. Caminata, S. Caprioli, A. Celentano, S. Davini, A. Marini, G. Sobrero

Abstract: Plastic scintillators have become increasingly important in particle physics for time-of-flight and calorimetry measurements. Their light yield and the possibility of customizing their geometry make them also attractive for the construction of active vetoes in rare event physics experiments. For this purpose, some commercial plastic scintillators (purchased from Eljen Technology) were tested in cr… ▽ More Plastic scintillators have become increasingly important in particle physics for time-of-flight and calorimetry measurements. Their light yield and the possibility of customizing their geometry make them also attractive for the construction of active vetoes in rare event physics experiments. For this purpose, some commercial plastic scintillators (purchased from Eljen Technology) were tested in cryogenic environments (liquid nitrogen and liquid helium). Their relative light yield was estimated by comparing the data acquired at room temperature with those acquired at cryogenic temperatures. Finally, estimates of the variation of the light yield at cryogenic temperatures were obtained. △ Less

Submitted 26 May, 2023; v1 submitted 6 March, 2023; originally announced March 2023.

Sensitivity projections for a dual-phase argon TPC optimized for light dark matter searches through the ionization channel

Authors: P. Agnes, I. Ahmad, S. Albergo, I. F. M. Albuquerque, T. Alexander, A. K. Alton, P. Amaudruz, M. Atzori Corona, D. J. Auty, M. Ave, I. Ch. Avetisov, R. I. Avetisov, O. Azzolini, H. O. Back, Z. Balmforth, V. Barbarian, A. Barrado Olmedo, P. Barrillon, A. Basco, G. Batignani, E. Berzin, A. Bondar, W. M. Bonivento, E. Borisova, B. Bottino , et al. (274 additional authors not shown)

Abstract: Dark matter lighter than 10 GeV/c$^2$ encompasses a promising range of candidates. A conceptual design for a new detector, DarkSide-LowMass, is presented, based on the DarkSide-50 detector and progress toward DarkSide-20k, optimized for a low-threshold electron-counting measurement. Sensitivity to light dark matter is explored for various potential energy thresholds and background rates. These stu… ▽ More Dark matter lighter than 10 GeV/c$^2$ encompasses a promising range of candidates. A conceptual design for a new detector, DarkSide-LowMass, is presented, based on the DarkSide-50 detector and progress toward DarkSide-20k, optimized for a low-threshold electron-counting measurement. Sensitivity to light dark matter is explored for various potential energy thresholds and background rates. These studies show that DarkSide-LowMass can achieve sensitivity to light dark matter down to the solar neutrino floor for GeV-scale masses and significant sensitivity down to 10 MeV/c$^2$ considering the Migdal effect or interactions with electrons. Requirements for optimizing the detector's sensitivity are explored, as are potential sensitivity gains from modeling and mitigating spurious electron backgrounds that may dominate the signal at the lowest energies. △ Less

Submitted 20 June, 2023; v1 submitted 2 September, 2022; originally announced September 2022.

Journal ref: Phys. Rev. D 107, 112006 (2023)

Spatial dissipative solitons in graphene-based active random metamaterials

Authors: Ashis Paul, Andrea Marini, Samudra Roy

Abstract: We investigate dissipative nonlinear dynamics in graphene-based active metamaterials composed of randomly dispersed graphene nano-flakes embedded within an externally pumped gain medium. We observe that graphene saturable nonlinearity produces a sub-critical bifurcation of nonlinear modes, enabling self-organization of the emitted radiation into several dissipative soliton structures with distinct… ▽ More We investigate dissipative nonlinear dynamics in graphene-based active metamaterials composed of randomly dispersed graphene nano-flakes embedded within an externally pumped gain medium. We observe that graphene saturable nonlinearity produces a sub-critical bifurcation of nonlinear modes, enabling self-organization of the emitted radiation into several dissipative soliton structures with distinct topological charges. We systematically investigate the existence domains of such nonlinear waves and their spatio-temporal dynamics, finding that soliton vortices are unstable, thus enabling self-organization into single dissipative structures with vanishing topological charge, independently of the shape of the graphene nano-flakes. Our results shed light on self-organization of coherent radiation structures in disordered systems and are relevant for future cavity-free lasers and amplifier designs. △ Less

Submitted 12 January, 2022; originally announced January 2022.

Free-carrier-induced nonlinear dynamics in hybrid graphene-based photonic waveguides

Authors: Ambaresh Sahoo, Andrea Marini, Samudra Roy

Abstract: We develop from first principles a theoretical model for infrared pulse propagation in graphene-covered hybrid waveguides. We model electron dynamics in graphene by Bloch equations, enabling the derivation of the nonlinear conductivity and of a rate equation accounting for free-carrier generation. Radiation propagation is modeled through a generalized nonlinear Schrödinger equation for the field e… ▽ More We develop from first principles a theoretical model for infrared pulse propagation in graphene-covered hybrid waveguides. We model electron dynamics in graphene by Bloch equations, enabling the derivation of the nonlinear conductivity and of a rate equation accounting for free-carrier generation. Radiation propagation is modeled through a generalized nonlinear Schrödinger equation for the field envelope coupled with the rate equation accounting for the generation of free carriers in graphene. Our numerical simulations clearly indicate that unperturbed Kerr solitons accelerate due to the carrier-induced index change and experience a strong self-induced spectral blueshift. Our numerical results are fully explained by semianalytical predictions based on soliton perturbation theory. △ Less

Submitted 21 December, 2021; v1 submitted 30 August, 2021; originally announced August 2021.

Comments: 7 pages, 4 figures, Typo error in the value of $e_0$ in page-3 subsection-B has been rectified in version 3 of the manuscript

R\&D evaluation methodology based on group-AHP with uncertainty

Authors: Alberto Garinei, Emanuele Piccioni, Massimiliano Proietti, Andrea Marini, Stefano Speziali, Marcello Marconi, Raffaella Di Sante, Sara Casaccia, Paolo Castellini, Milena Martarelli, Nicola Paone, Gian Marco Revel, Lorenzo Scalise, Marco Arnesano, Paolo Chiariotti, Roberto Montanini, Antonino Quattrocchi, Sergio Silvestri, Giorgio Ficco, Emanuele Rizzuto, Andrea Scorza, Matteo Lancini, Gianluca Rossi, Roberto Marsili, Emanuele Zappa , et al. (3 additional authors not shown)

Abstract: In this paper, we present an approach to evaluate Research \& Development (R\&D) performance based on the Analytic Hierarchy Process (AHP) method. Through a set of questionnaires submitted to a team of experts, we single out a set of indicators needed for R\&D performance evaluation. The indicators, together with the corresponding criteria, form the basic hierarchical structure of the AHP method.… ▽ More In this paper, we present an approach to evaluate Research \& Development (R\&D) performance based on the Analytic Hierarchy Process (AHP) method. Through a set of questionnaires submitted to a team of experts, we single out a set of indicators needed for R\&D performance evaluation. The indicators, together with the corresponding criteria, form the basic hierarchical structure of the AHP method. The numerical values associated with all the indicators are then used to assign a score to a given R\&D project. In order to aggregate consistently the values taken on by the different indicators, we operate on them so that they are mapped to dimensionless quantities lying in a unit interval. This is achieved by employing the empirical Cumulative Density Function (CDF) for each of the indicators. We give a thorough discussion on how to assign a score to an R\&D project along with the corresponding uncertainty due to possible inconsistencies of the decision process. A particular example of R\&D performance is finally considered. △ Less

Submitted 22 November, 2021; v1 submitted 5 August, 2021; originally announced August 2021.

Comments: 13 pages, 2 figures

Non-linear self-driven spectral tuning of Extreme Ultraviolet Femtosecond Pulses in monoatomic materials

Authors: Carino Ferrante, Emiliano Principi, Andrea Marini, Giovanni Batignani, Giuseppe Fumero, Alessandra Virga, Laura Foglia, Riccardo Mincigrucci, Alberto Simoncig, Carlo Spezzani, Claudio Masciovecchio, Tullio Scopigno

Abstract: Self-action nonlinearity is a key aspect -- either as a foundational element or a detrimental factor -- of several optical spectroscopies and photonic devices. Supercontinuum generation, wavelength converters and chirped pulse amplification are just a few examples. The recent advent of Free Electron Lasers (FEL) fostered building on nonlinearity to propose new concepts and extend optical wavelengt… ▽ More Self-action nonlinearity is a key aspect -- either as a foundational element or a detrimental factor -- of several optical spectroscopies and photonic devices. Supercontinuum generation, wavelength converters and chirped pulse amplification are just a few examples. The recent advent of Free Electron Lasers (FEL) fostered building on nonlinearity to propose new concepts and extend optical wavelengths paradigms for extreme ultraviolet (EUV) and X-ray regimes. No evidence for intrapulse dynamics, however, has been reported at such short wavelengths, where the light-matter interactions are ruled by the sharp absorption edges of core-electrons. Here, we provide experimental evidence for self-phase modulation of femtosecond FEL pulses, which we exploit for fine self-driven spectral tunability by interaction with sub-micrometric foils of selected monoatomic materials. Moving the pulse wavelength across the absorption edge, the spectral profile changes from a non-linear spectral blue-shift to a red-shifted broadening. These findings are rationalized accounting for ultrafast ionization and delayed thermal response of highly excited electrons above and below threshold, respectively. △ Less

Submitted 19 April, 2021; originally announced April 2021.

Comments: 20 pages, 6 figures

Electromagnetic Isolation Induced by Time-Varying Metasurfaces: Non-Reciprocal Bragg Grating

Authors: Davide Ramaccia, Dimitrios L. Sounas, Angelica V. Marini, Alessandro Toscano, Filiberto Bilotti

Abstract: In this letter, we propose a magnet-less non-reciprocal isolating system based on time-varying metasurfaces. Two parallel time-varying metasurfaces, one for frequency up-conversion and one for down-conversion by the same amount, are used for realizing a region of space where incident waves from opposite directions experience an opposite Doppler frequency shift. As a result, any device within this… ▽ More In this letter, we propose a magnet-less non-reciprocal isolating system based on time-varying metasurfaces. Two parallel time-varying metasurfaces, one for frequency up-conversion and one for down-conversion by the same amount, are used for realizing a region of space where incident waves from opposite directions experience an opposite Doppler frequency shift. As a result, any device within this region becomes sensitive to the illumination direction, exhibiting a different scattering response from opposite directions and thus breaking reciprocity. Very importantly, thanks to the opposite frequency shift of the metasurfaces, the frequency of the transmitted electromagnetic field is the same as for the incident one. Here, we demonstrate this general approach by using a Bragg grating as the device between the time-varying metasurfaces. The combined structure of the metasurfaces and the grating exhibits different transmission and reflection properties for opposite illumination direction, thereby realizing an isolator. More broadly, this letter presents a strategy for converting any conventional electromagnetic device to a non-reciprocal one by placing it between two time-varying metasurfaces. This approach opens the door to several new non-reciprocal components based on thin and lightweight metasurfaces, which are simpler to realize compared to their volumetric counterparts. △ Less

Submitted 3 February, 2021; originally announced March 2021.

Journal ref: IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 11, pp. 1886-1890, Nov. 2020

Electric directional steering of cathodoluminescence from graphene-based hydrid nanostructures

Authors: Alessandro Ciattoni, Claudio Conti, Andrea Marini

Abstract: Controlling directional emission of nanophotonic radiation sources is fundamental to tailor radiation-matter interaction and to conceive highly efficient nanophotonic devices for on-chip wireless communication and information processing. Nanoantennas coupled to quantum emitters have proven to be very efficient radiation routers, while electrical control of unidirectional emission has been achieved… ▽ More Controlling directional emission of nanophotonic radiation sources is fundamental to tailor radiation-matter interaction and to conceive highly efficient nanophotonic devices for on-chip wireless communication and information processing. Nanoantennas coupled to quantum emitters have proven to be very efficient radiation routers, while electrical control of unidirectional emission has been achieved through inelastic tunneling of electrons. Here we prove that the radiation emitted from the interaction of a high-energy electron beam with a graphene-nanoparticle composite has beaming directions which can be made to continuously span the full circle even through small variations of the graphene Fermi energy. Emission directionality stems from the interference between the double cone shaped electron transition radiation and the nanoparticle dipolar diffraction radiation. Tunability is enabled since the interference is ruled by the nanoparticle dipole moment whose amplitude and phase are driven by the hybrid plasmonic resonances of the composite and the absolute phase of the graphene plasmonic polariton launched by the electron, respectively. The flexibility of our method provides a way to exploit graphene plasmon physics to conceive improved nanosources with ultrafast reconfigurable radiation patterns. △ Less

Submitted 18 October, 2020; originally announced October 2020.

Journal ref: Phys. Rev. Applied 15, 054016 (2021)

Time-dependent screening explains the ultrafast excitonic signal rise in 2D semiconductors

Authors: Valerie Smejkal, Florian Libisch, Alejandro Molina-Sanchez, Ludger Wirtz, Andrea Marini

Abstract: We calculate the time evolution of the transient reflection signal in an MoS$_2$ monolayer on a SiO$_2$/Si substrate using first-principles out-of-equilibrium real-time methods. Our simulations provide a simple and intuitive physical picture for the delayed, yet ultrafast, evolution of the signal whose rise time depends on the excess energy of the pump laser: at laser energies above the A- and B-e… ▽ More We calculate the time evolution of the transient reflection signal in an MoS$_2$ monolayer on a SiO$_2$/Si substrate using first-principles out-of-equilibrium real-time methods. Our simulations provide a simple and intuitive physical picture for the delayed, yet ultrafast, evolution of the signal whose rise time depends on the excess energy of the pump laser: at laser energies above the A- and B-exciton, the pump pulse excites electrons and holes far away from the K valleys in the first Brillouin zone. Electron-phonon and hole-phonon scattering lead to a gradual relaxation of the carriers towards small $\textit{Active Excitonic Regions}$ around K, enhancing the dielectric screening. The accompanying time-dependent band gap renormalization dominates over Pauli blocking and the excitonic binding energy renormalization. This explains the delayed buildup of the transient reflection signal of the probe pulse, in excellent agreement with recent experimental data. Our results show that the observed delay is not a unique signature of an exciton formation process but rather caused by coordinated carrier dynamics and its influence on the screening. △ Less

Submitted 6 October, 2020; originally announced October 2020.

Electric control of spin orbit coupling in graphene-based nanostructures with broken rotational symmetry

Authors: Alessandro Ciattoni, Claudio Conti, Anatoly Zayats, Andrea Marini

Abstract: Spin and angular momenta of light are important degrees of freedom in nanophotonics which control light propagation, optical forces and information encoding. Typically, optical angular momentum is generated using q-plates or spatial light modulators. Here, we show that graphene-supported plasmonic nanostructures with broken rotational symmetry provide a surprising spin to orbital angular momentum… ▽ More Spin and angular momenta of light are important degrees of freedom in nanophotonics which control light propagation, optical forces and information encoding. Typically, optical angular momentum is generated using q-plates or spatial light modulators. Here, we show that graphene-supported plasmonic nanostructures with broken rotational symmetry provide a surprising spin to orbital angular momentum conversion, which can be continuously controlled by changing the electrochemical potential of graphene. Upon resonant illumination by a circularly polarized plane wave, a polygonal array of indium-tin-oxide nanoparticles on a graphene sheet generates scattered field carrying electrically-tunable orbital angular momentum. This unique photonic spin-orbit coupling occurs due to the strong coupling of graphene plasmon polaritons and localised surface plasmons of the nanoparticles and leads to the controlled directional excitation of graphene plasmons. The tuneable spin-orbit conversion pave the way to high-rate information encoding in optical communications, electric steering functionalities in optical tweezers, and nanorouting of higher-dimensional entangled photon states. △ Less

Submitted 27 February, 2020; originally announced February 2020.

Strongly coupled coherent phonons in single-layer MoS$_2$

Authors: C. Trovatello, H. P. C. Miranda, A. Molina-Sánchez, R. Borrego Varillas, C. Manzoni, L. Moretti, L. Ganzer, M. Maiuri, J. Wang, D. Dumcenco, A. Kis, L. Wirtz, A. Marini, G. Soavi, A. C. Ferrari, G. Cerullo, D. Sangalli, S. Dal Conte

Abstract: We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution ($\sim$20fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single layer (1L) MoS$_2$, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), wher… ▽ More We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution ($\sim$20fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single layer (1L) MoS$_2$, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane $A'_{1}$ phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a timescale of few tens fs. We observe an enhancement by almost two orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab initio calculations of the change in 1L-MoS$_2$ band structure induced by the $A'_{1}$ phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. This demonstrates that CP excitation in 1L-MoS$_2$ can be described as a Raman-like scattering process. These results explain the CP generation process in 1L-TMDs, paving the way for coherent all-optical control of excitons in layered materials in the THz frequency range. △ Less

Submitted 29 December, 2019; originally announced December 2019.

Journal ref: ACS Nano 14, 5700 (2020)

Broadband optical parametric amplification by two-dimensional semiconductors

Authors: Chiara Trovatello, Andrea Marini, Xinyi Xu, Changhwan Lee, Fang Liu, Nicola Curreli, Cristian Manzoni, Stefano Dal Conte, Kaiyuan Yao, Alessandro Ciattoni, James Hone, Xiaoyang Zhu, P. James Schuck, Giulio Cerullo

Abstract: Optical parametric amplification is a second-order nonlinear process whereby an optical signal is amplified by a pump via the generation of an idler field. It is the key ingredient of tunable sources of radiation that play an important role in several photonic applications. This mechanism is inherently related to spontaneous parametric down-conversion that currently constitutes the building block… ▽ More Optical parametric amplification is a second-order nonlinear process whereby an optical signal is amplified by a pump via the generation of an idler field. It is the key ingredient of tunable sources of radiation that play an important role in several photonic applications. This mechanism is inherently related to spontaneous parametric down-conversion that currently constitutes the building block for entangled photon pair generation, which has been exploited in modern quantum technologies ranging from computing to communications and cryptography. Here we demonstrate single-pass optical parametric amplification at the ultimate thickness limit; using semiconducting transition-metal dichalcogenides, we show that amplification can be attained over a propagation through a single atomic layer. Such a second-order nonlinear interaction at the 2D limit bypasses phase-matching requirements and achieves ultrabroad amplification bandwidths. The amplification process is independent on the in-plane polarization of the impinging signal and pump fields. First-principle calculations confirm the observed polarization invariance and linear relationship between idler and pump powers. Our results pave the way for the development of atom-sized tunable sources of radiation with applications in nanophotonics and quantum information technology. △ Less

Submitted 22 December, 2019; originally announced December 2019.

Goos-Hänchen and Imbert-Fedorov Shifts for Epsilon-Near-Zero Materials

Authors: Arttu Nieminen, Andrea marini, Marco Ornigotti

Abstract: We investigate the reflection of a Gaussian beam impinging upon the surface of an epsilon-near-zero (ENZ) medium. In particular, we discuss the occurrence of Goos-Hänchen and Imbert-Fedorov shifts. Our calculations reveal that spatial shifts are significantly enhanced owing to the ENZ nature of the medium, and that their value and angular position can be tuned by tuning the plasma frequency of the… ▽ More We investigate the reflection of a Gaussian beam impinging upon the surface of an epsilon-near-zero (ENZ) medium. In particular, we discuss the occurrence of Goos-Hänchen and Imbert-Fedorov shifts. Our calculations reveal that spatial shifts are significantly enhanced owing to the ENZ nature of the medium, and that their value and angular position can be tuned by tuning the plasma frequency of the medium. △ Less

Submitted 20 November, 2019; originally announced November 2019.

Heat-induced soliton self-frequency redshift in the ultrafast nonlinear dynamics of active plasmonic waveguides

Authors: Ambaresh Sahoo, Andrea Marini, Samudra Roy

Abstract: We investigate the ultrafast nonlinear dynamics of light emitted in an active plasmonic waveguide composed of a thin film of gold sandwiched by two silicon layers immersed in externally pumped Al$_2$O$_3$:Er$^{3+}$. We model optical propagation in such a dissipative system through a generalized cubic Ginzburg-Landau equation accounting for the amplification of the active medium and the effect of a… ▽ More We investigate the ultrafast nonlinear dynamics of light emitted in an active plasmonic waveguide composed of a thin film of gold sandwiched by two silicon layers immersed in externally pumped Al$_2$O$_3$:Er$^{3+}$. We model optical propagation in such a dissipative system through a generalized cubic Ginzburg-Landau equation accounting for the amplification of the active medium and the effect of absorption and thermo-modulational nonlinearity of gold. We find that heating heavily affects the propagation of temporal dissipative solitons in such a plasmonic waveguide by producing a soliton self-frequency redshift accompanied by soliton deceleration in the time domain. By adopting a semi-analytical variational approach, we evaluate the dependence of the self-induced redshift by deriving a set of coupled differential equations for the pulse parameters. These equations provide physical insight into the complex nonlinear dynamics through simple approximate analytic expressions for temporal and frequency shifts. Such analytical predictions are found in excellent agreement with direct numerical simulations of the generalized cubic Ginzburg-Landau equation. Our results provide a general understanding of ultrafast nonlinear dynamics in gold-based active plasmonic waveguides, as in particular the spectral shaping properties of propagating optical pulses. △ Less

Submitted 12 April, 2019; originally announced April 2019.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. A 100, 013848 (2019)

Many-body perturbation theory calculations using the yambo code

Authors: D. Sangalli, A. Ferretti, H. Miranda, C. Attaccalite, I. Marri, E. Cannuccia, P. Melo, M. Marsili, F. Paleari, A. Marrazzo, G. Prandini, P. Bonfà, M. O. Atambo, F. Affinito, M. Palummo, A. Molina-Sánchez, C. Hogan, M. Grüning, D. Varsano, A. Marini

Abstract: yambo is an open source project aimed at studying excited state properties of condensed matter systems from first principles using many-body methods. As input, yambo requires ground state electronic structure data as computed by density functional theory codes such as quantum-espresso and abinit. yambo's capabilities include the calculation of linear response quantities (both independent-particle… ▽ More yambo is an open source project aimed at studying excited state properties of condensed matter systems from first principles using many-body methods. As input, yambo requires ground state electronic structure data as computed by density functional theory codes such as quantum-espresso and abinit. yambo's capabilities include the calculation of linear response quantities (both independent-particle and including electron-hole interactions), quasi-particle corrections based on the GW formalism, optical absorption, and other spectroscopic quantities. Here we describe recent developments ranging from the inclusion of important but oft-neglected physical effects such as electron-phonon interactions to the implementation of a real-time propagation scheme for simulating linear and non-linear optical properties. Improvements to numerical algorithms and the user interface are outlined. Particular emphasis is given to the new and efficient parallel structure that makes it possible to exploit modern high performance computing architectures. Finally, we demonstrate the possibility to automate workflows by interfacing with the yambopy and AiiDA software tools. △ Less

Submitted 7 June, 2019; v1 submitted 11 February, 2019; originally announced February 2019.

Journal ref: Journal of Physics: Condensed Matter, Volume 31, Number 32 (2019)

Optical harmonic generation in monolayer group-VI transition metal dichalcogenides

Authors: Anton Autere, Henri Jussila, Andrea Marini, J. R. M. Saavedra, Yunyun Dai, Antti Saynatjoki, Lasse Karvonen, He Yang, Babak Amirsolaimani, Robert A. Norwood, Nasser Peyghambarian, Harri Lipsanen, Khanh Kieu, Francisco J. Garcia de Abajo, Zhipei Sun

Abstract: Monolayer transition metal dichalcogenides (TMDs) exhibit high nonlinear optical (NLO) susceptibilities. Experiments on MoS$_2$ have indeed revealed very large second-order ($χ^{(2)}$) and third-order ($χ^{(3)}$) optical susceptibilities. However, third harmonic generation results of other layered TMDs has not been reported. Furthermore, the reported $χ^{(2)}$ and $χ^{(3)}$ of MoS$_2$ vary by seve… ▽ More Monolayer transition metal dichalcogenides (TMDs) exhibit high nonlinear optical (NLO) susceptibilities. Experiments on MoS$_2$ have indeed revealed very large second-order ($χ^{(2)}$) and third-order ($χ^{(3)}$) optical susceptibilities. However, third harmonic generation results of other layered TMDs has not been reported. Furthermore, the reported $χ^{(2)}$ and $χ^{(3)}$ of MoS$_2$ vary by several orders of magnitude, and a reliable quantitative comparison of optical nonlinearities across different TMDs has remained elusive. Here, we investigate second- and third-harmonic generation, and three-photon photoluminescence in TMDs. Specifically, we present an experimental study of $χ^{(2)}$, and $χ^{(3)}$ of four common TMD materials (\ce{MoS2}, \ce{MoSe2}, \ce{WS2} and \ce{WSe2}) by placing different TMD flakes in close proximity to each other on a common substrate, allowing their NLO properties to be accurately obtained from a single measurement. $χ^{(2)}$ and $χ^{(3)}$ of the four monolayer TMDs have been compared, indicating that they exhibit distinct NLO responses. We further present theoretical simulations of these susceptibilities in qualitative agreement with the measurements. Our comparative studies of the NLO responses of different two-dimensional layered materials allow us to select the best candidates for atomic-scale nonlinear photonic applications, such as frequency conversion and all-optical signal processing. △ Less

Submitted 6 September, 2018; v1 submitted 28 August, 2018; originally announced August 2018.

Comments: 7 pages, 5 figures, To be appeared in Physical Review B

Journal ref: Phys. Rev. B 98, 115426 (2018)

Collision quenching in the ultrafast dynamics of plasmonic materials

Authors: Andrea Marini, Alessandro Ciattoni, Claudio Conti

Abstract: We explore the nonlinear response of plasmonic materials driven by ultrashort pulses of electromagnetic radiation with temporal duration of few femtoseconds and high peak intensity. By developing the Fokker-Planck-Landau theory of electron collisions, we solve analytically the collisional integral and derive a novel set of hydrodynamical equations accounting for plasma dynamics at ultrashort time… ▽ More We explore the nonlinear response of plasmonic materials driven by ultrashort pulses of electromagnetic radiation with temporal duration of few femtoseconds and high peak intensity. By developing the Fokker-Planck-Landau theory of electron collisions, we solve analytically the collisional integral and derive a novel set of hydrodynamical equations accounting for plasma dynamics at ultrashort time scales. While in the limit of small light intensities we recover the well established Drude model of plasmas, in the high intensity limit we observe nonlinear quenching of collision-induced damping leading to absorption saturation. Our results provide a general background to understand electron dynamics in plasmonic materials with promising photonic applications in the manipulation of plasma waves with reduced absorption at the femtosecond time scale. △ Less

Submitted 10 August, 2018; originally announced August 2018.

Plasmon-enhanced spin-orbit interaction of light in graphene

Authors: A. Ciattoni, C. Rizza, H. W. H. Lee, C. Conti, A. Marini

Abstract: We develop a novel theoretical framework describing polariton-enhanced spin-orbit interaction of light on the surface of two-dimensional media. Starting from the integral formulation of electromagnetic scattering, we exploit the reduced dimensionality of the system to introduce a quantum-like formalism particularly suitable to fully take advantage of rotational invariance. Our description is close… ▽ More We develop a novel theoretical framework describing polariton-enhanced spin-orbit interaction of light on the surface of two-dimensional media. Starting from the integral formulation of electromagnetic scattering, we exploit the reduced dimensionality of the system to introduce a quantum-like formalism particularly suitable to fully take advantage of rotational invariance. Our description is closely related to that of a fictitious spin one quantum particle living in the atomically thin medium, whose orbital, spin and total angular momenta play a key role in the scattering process. Conservation of total angular momentum upon scattering enables to physically unveil the interaction between radiation and the two-dimensional material along with the detailed exchange processes among orbital and spin components. In addition, we specialize our model to doped extended graphene, finding such spin-orbit interaction to be dramatically enhanced by the excitation of surface plasmon polaritons propagating radially along the graphene sheet. We provide several examples of the enormous possibilities offered by plasmon-enhanced spin-orbit interaction of light including vortex generation, mixing, and engineering of tunable deep subwavelength arrays of optical traps in the near field. Our results hold great potential for the development of nano-scaled quantum active elements and logic gates for the manipulation of hyper-entangled photon states as well as for the design of artificial media imprinted by engineered photonic lattices tweezing cold atoms into the desired patterns. △ Less

Submitted 27 April, 2018; originally announced April 2018.

Ultrafast Charge Migration in XUV Photoexcited Phenylalanine: a First-Principles Study Based on Real-Time Nonequilibrium Green's Functions

Authors: E. Perfetto, D. Sangalli, A. Marini, G. Stefanucci

Abstract: The early stage density oscillations of the electronic charge in molecules irradiated by an attosecond XUV pulse takes place on femto- or subfemtosecond timescales. This ultrafast charge migration process is a central topic in attoscience as it dictates the relaxation pathways of the molecular structure. A predictive quantum theory of ultrafast charge migration should incorporate the atomistic det… ▽ More The early stage density oscillations of the electronic charge in molecules irradiated by an attosecond XUV pulse takes place on femto- or subfemtosecond timescales. This ultrafast charge migration process is a central topic in attoscience as it dictates the relaxation pathways of the molecular structure. A predictive quantum theory of ultrafast charge migration should incorporate the atomistic details of the molecule, electronic correlations and the multitude of ionization channels activated by the broad-bandwidth XUV pulse. In this work we propose a first-principles Non Equilibrium Green's Function method fulfilling all three requirements, and apply it to a recent experiment on the photoexcited phenylalanine aminoacid. Our results show that dynamical correlations are necessary for a quantitative overall agreement with the experimental data. In particular, we are able to capture the transient oscillations at frequencies 0.15PHz and 0.30PHz in the hole density of the amine group, as well as their suppression and the concomitant development of a new oscillation at frequency 0.25PHz after about 14 femtoseconds. △ Less

Submitted 15 March, 2018; originally announced March 2018.

Comments: 7 pages, 5 figures

Journal ref: Journal of Physical Chemistry Letters 9, 1353 (2018)

Diode-like asymmetric transmission in ultrathin hyperbolic epsilon-near-zero slabs: extreme anisotropy mimicking chirality

Authors: Carlo Rizza, Xin Li, Andrea Di Falco, Andrea Marini, Elia Palange, Alessandro Ciattoni

Abstract: We demonstrate that a strong asymmetric transmission for forward and backward propagation of tilted circular polarized optical waves is supported by ultrathin epsilon-near-zero hyperbolic slabs. We find that, remarkably, this effect is solely triggered by anisotropy without resorting to any breaking of reciprocity and chiral symmetries or spatial nonlocal effects. In addition, we show that the asy… ▽ More We demonstrate that a strong asymmetric transmission for forward and backward propagation of tilted circular polarized optical waves is supported by ultrathin epsilon-near-zero hyperbolic slabs. We find that, remarkably, this effect is solely triggered by anisotropy without resorting to any breaking of reciprocity and chiral symmetries or spatial nonlocal effects. In addition, we show that the asymmetric transmission undergoes a dramatic enhancement if the slab is hyperbolic in the epsilon-near-zero regime. This happens since, close to epsilon-near-zero point, the hyperbolic dispersion activates etalon resonances where extraordinary waves accumulate propagation phase even though the slab is ultrathin. The proposed strategy holds promise for realizing ultra-compact and efficient polarization devices at different frequency bands. △ Less

Submitted 20 February, 2018; originally announced February 2018.

Comments: 4 figures, submitted to PRApplied

Phase-matching-free parametric oscillators based on two dimensional semiconductors

Authors: A. Ciattoni, A. Marini, C. Rizza, C. Conti

Abstract: Optical parametric oscillators are widely-used pulsed and continuous-wave tunable sources for innumerable applications, as in quantum technologies, imaging and biophysics. A key drawback is material dispersion imposing the phase-matching condition that generally entails a complex setup design, thus hindering tunability and miniaturization. Here we show that the burden of phase-matching is surprisi… ▽ More Optical parametric oscillators are widely-used pulsed and continuous-wave tunable sources for innumerable applications, as in quantum technologies, imaging and biophysics. A key drawback is material dispersion imposing the phase-matching condition that generally entails a complex setup design, thus hindering tunability and miniaturization. Here we show that the burden of phase-matching is surprisingly absent in parametric micro-resonators adopting monolayer transition-metal dichalcogenides as quadratic nonlinear materials. By the exact solution of nonlinear Maxwell equations and first-principle calculation of the semiconductor nonlinear response, we devise a novel kind of phase-matching-free miniaturized parametric oscillator operating at conventional pump intensities. We find that different two-dimensional semiconductors yield degenerate and non-degenerate emission at various spectral regions thanks to doubly-resonant mode excitation, which can be tuned through the incidence angle of the external pump laser. In addition we show that high-frequency electrical modulation can be achieved by doping through electrical gating that efficiently shifts the parametric oscillation threshold. Our results pave the way for new ultra-fast tunable micron-sized sources of entangled photons, a key device underpinning any quantum protocol. Highly-miniaturized optical parametric oscillators may also be employed in lab-on-chip technologies for biophysics, environmental pollution detection and security. △ Less

Submitted 27 July, 2017; originally announced July 2017.

Comments: 22 pages, 7 figures

Efficient vortex generation in sub-wavelength epsilon-near-zero slabs

Authors: Alessandro Ciattoni, Andrea Marini, Carlo Rizza

Abstract: We show that a homogeneous and isotropic slab, illuminated by a circularly polarized beam with no topological charge, produces vortices of order two in the opposite circularly polarized components of the reflected and transmitted fields, as a consequence of the difference between transverse magnetic and transverse electric dynamics. In the epsilon-near-zero regime, we find that vortex generation i… ▽ More We show that a homogeneous and isotropic slab, illuminated by a circularly polarized beam with no topological charge, produces vortices of order two in the opposite circularly polarized components of the reflected and transmitted fields, as a consequence of the difference between transverse magnetic and transverse electric dynamics. In the epsilon-near-zero regime, we find that vortex generation is remarkably efficient in sub-wavelength thick slabs up to the paraxial regime. This physically stems from the fact that a vacuum paraxial field can excite a nonparaxial field inside an epsilon-near-zero slab since it hosts slowly varying fields over physically large portion of the bulk. Our theoretical predictions indicate that epsilon-near-zero media hold great potential as nanophotonic elements for manipulating the angular momentum of the radiation, since they are available without resorting to complicated micro/nano fabrication processes and can operate even at very small (ultraviolet) wavelengths. △ Less

Submitted 5 October, 2016; originally announced October 2016.

Journal ref: Phys. Rev. Lett. 118, 104301 (2017)

Plasmon-assisted high-harmonic generation in graphene

Authors: Joel D. Cox, Andrea Marini, F. Javier García de Abajo

Abstract: High-harmonic generation (HHG) in condensed-matter systems is both a source of fundamental insight into quantum electron motion and a promising candidate to realize compact ultraviolet and ultrafast light sources. Here we argue that the large light intensity required for this phenomenon to occur can be reached by exploiting localized plasmons in conducting nanostructures. In particular, we demonst… ▽ More High-harmonic generation (HHG) in condensed-matter systems is both a source of fundamental insight into quantum electron motion and a promising candidate to realize compact ultraviolet and ultrafast light sources. Here we argue that the large light intensity required for this phenomenon to occur can be reached by exploiting localized plasmons in conducting nanostructures. In particular, we demonstrate that doped graphene nanostructures combine a strong plasmonic near-field enhancement and a pronounced intrinsic nonlinearity that result in efficient broadband HHG within a single material platform. We extract this conclusion from time-domain simulations using two complementary nonperturbative approaches based on atomistic one-electron density-matrix and massless Dirac-fermion Bloch-equation pictures. High harmonics are predicted to be emitted with unprecedentedly large intensity by tuning the incident light to the localized plasmons of ribbons and finite islands. In contrast to atomic systems, we observe no cutoff in harmonic order. Our results support the strong potential of nanostructured graphene as a robust, electrically tunable platform for HHG. △ Less

Submitted 30 September, 2016; originally announced September 2016.

Comments: 8 pages, 5 figures

Journal ref: Nature Communications 8, 14380 (2017)

Theory of graphene saturable absorption

Authors: A. Marini, J. D. Cox, F. J. Garcia de Abajo

Abstract: Saturable absorption is a non-perturbative nonlinear optical phenomenon that plays a pivotal role in the generation of ultrafast light pulses. Here we show that this effect emerges in graphene at unprecedentedly low light intensities, thus opening avenues to new nonlinear physics and applications in optical technology. Specifically, we theoretically investigate saturable absorption in extended gra… ▽ More Saturable absorption is a non-perturbative nonlinear optical phenomenon that plays a pivotal role in the generation of ultrafast light pulses. Here we show that this effect emerges in graphene at unprecedentedly low light intensities, thus opening avenues to new nonlinear physics and applications in optical technology. Specifically, we theoretically investigate saturable absorption in extended graphene by developing a non-perturbative single-particle approach, describing conduction-electron dynamics in the atomically-thin material using the two-dimensional Dirac equation for massless Dirac fermions, which is recast in the form of generalized Bloch equations. By solving the electron dynamics non-perturbatively, we account for both interband and intraband contributions to the intensity-dependent saturated conductivity and conclude that the former dominates regardless of the intrinsic doping state of the material. The results are in excellent agreement with atomistic quantum-mechanical simulations including higher-band effects. Additionally, we find that the modulation depth of saturable absorption in graphene can be electrically manipulated through an externally applied gate voltage. Our results are relevant for the development of graphene-based optoelectronic devices, as well as for applications in mode-locking and random lasers. △ Less

Submitted 20 May, 2016; originally announced May 2016.

Journal ref: Phys. Rev. B 95, 125408 (2017)

Dynamical centrosymmetry breaking in graphene

Authors: David N. Carvalho, Andrea Marini, Fabio Biancalana

Abstract: We discover an unusual phenomenon that occurs when a graphene monolayer is illuminated by a short and intense pulse at normal incidence. Due to the pulse-induced oscillations of the Dirac cones, a dynamical breaking of the layer's centrosymmetry takes place, leading to the generation of second harmonic waves. We prove that this result can only be found by using the full Dirac equation and show tha… ▽ More We discover an unusual phenomenon that occurs when a graphene monolayer is illuminated by a short and intense pulse at normal incidence. Due to the pulse-induced oscillations of the Dirac cones, a dynamical breaking of the layer's centrosymmetry takes place, leading to the generation of second harmonic waves. We prove that this result can only be found by using the full Dirac equation and show that the widely used semiconductor Bloch equations fail to reproduce this and some other important physics of graphene. Our results open new windows in the understanding of nonlinear light-matter interactions in a wide variety of new 2D materials with a gapped or ungapped Dirac-like dispersion. △ Less

Submitted 30 April, 2016; originally announced May 2016.

All-optical modulation in wavelength-sized epsilon-near-zero media

Authors: Alessandro Ciattoni, Andrea Marini, Carlo Rizza

Abstract: We investigate the interaction of two pulses (pump and probe) scattered by a nonlinear epsilon-near-zero (ENZ) slab whose thickness is comparable with the ENZ wavelength. We show that when the probe has a narrow spectrum localized around the ENZ wavelength its transmission is dramatically affected by the intensity of the pump. Conversely, if the probe is not in the ENZ regime, its propagation is n… ▽ More We investigate the interaction of two pulses (pump and probe) scattered by a nonlinear epsilon-near-zero (ENZ) slab whose thickness is comparable with the ENZ wavelength. We show that when the probe has a narrow spectrum localized around the ENZ wavelength its transmission is dramatically affected by the intensity of the pump. Conversely, if the probe is not in the ENZ regime, its propagation is not noticeably affected by the pump. Such all-optical modulation is due to the oversensitive character of the ENZ regime and it is so efficient to even occur in a wavelength thick slab. △ Less

Submitted 4 April, 2016; originally announced April 2016.

Comments: 4 pages, 2 figures

Non equilibrium optical properties in semiconductors from first--principles: a combined theoretical and experimental study of bulk silicon

Authors: Davide Sangalli, Stefano Dal Conte, Cristian Manzoni, Giulio Cerullo, Andrea Marini

Abstract: The calculation of the equilibrium optical properties of bulk silicon by using the Bethe--Salpeter equation solved in the Kohn--Sham basis represents a cornerstone in the development of an ab--initio approach to the optical and electronic properties of materials. Nevertheless calculations of the {\em transient} optical spectrum using the same efficient and successful scheme are scarce. We report,… ▽ More The calculation of the equilibrium optical properties of bulk silicon by using the Bethe--Salpeter equation solved in the Kohn--Sham basis represents a cornerstone in the development of an ab--initio approach to the optical and electronic properties of materials. Nevertheless calculations of the {\em transient} optical spectrum using the same efficient and successful scheme are scarce. We report, here, a joint theoretical and experimental study of the transient reflectivity spectrum of bulk silicon. Femtosecond transient reflectivity is compared to a parameter--free calculation based on the non--equilibrium Bethe--Salpeter equation. By providing an accurate description of the experimental results we disclose the different phenomena that determine the transient optical response of a semiconductor. We give a parameter--free interpretation of concepts like bleaching, photo--induced absorption and stimulated emission, beyond the Fermi golden rule. We also introduce the concept of optical gap renormalization, as a generalization of the known mechanism of band gap renormalization. The present scheme successfully describes the case of bulk silicon, showing its universality and accuracy. △ Less

Submitted 14 April, 2017; v1 submitted 1 March, 2016; originally announced March 2016.

Comments: 14 pages, 13 figures

Journal ref: Phys. Rev. B 93, 195205 (2016)

Dark Matter searches using gravitational wave bar detectors: quark nuggets and newtorites

Authors: M. Bassan, E. Coccia, S. D'Antonio, V. Fafone, G. Giordano, A. Marini, Y. Minenkov, I. Modena, G. V. Pallottino, G. Pizzella, A. Rocchi, F. Ronga, M. Visco

Abstract: Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nucl… ▽ More Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors Nautilus and Explorer is reported. The geometrical acceptance of the bar detectors is 19.5 $\rm m^2$ sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. The experimental limits we obtain are of interest because, for nuclearites of mass less than $10^{-5}$ g, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates. Particles with gravitational only interactions (newtorites) are another example. In this case the sensitivity is quite poor and a short discussion is reported on possible improvements. △ Less

Submitted 28 September, 2016; v1 submitted 19 December, 2015; originally announced December 2015.

Comments: published on Astroparticle Physics Sept 25th 2016 replaced fig 15

Graphene random laser

Authors: Andrea Marini, F. Javier García de Abajo

Abstract: Manipulating and controlling the optical energy flow inside random media is a research frontier of photonics and the basis of novel laser designs. In particular, light amplification in randomly dispersed active inclusions under external pumping has been extensively investigated, although it still lacks external tunability, reproducibility, and control over the beam spatial pattern, thus hindering… ▽ More Manipulating and controlling the optical energy flow inside random media is a research frontier of photonics and the basis of novel laser designs. In particular, light amplification in randomly dispersed active inclusions under external pumping has been extensively investigated, although it still lacks external tunability, reproducibility, and control over the beam spatial pattern, thus hindering its application in practical devices. Here we show that a graphene random metamaterial provides the means to overcome these limitations through its extraordinarily-low threshold for saturable absorption. The nonlinear properties of nano-graphene combined with an optically pumped gain medium allow us to controllably tune the system from chaotic to stable single-mode lasing. Our results hold great potential for the development of single-mode cavity-free lasers with engineered beam patterns in disordered media. △ Less

Submitted 14 December, 2015; originally announced December 2015.

Self-organization of frozen light in near-zero-index media with cubic nonlinearity

Authors: Andrea Marini, F. Javier Garcia de Abajo

Abstract: We theoretically demonstrate the existence of frozen light in near-zero-index media with cubic nonlinearity. Light is stopped to a standstill owing to the divergent wavelength and the vanishing group velocity, effectively rendering, through nonlinearity, a positive-epsilon trapping cavity carved in an otherwise slightly-negative-epsilon medium. By numerically solving Maxwell's equations, we find a… ▽ More We theoretically demonstrate the existence of frozen light in near-zero-index media with cubic nonlinearity. Light is stopped to a standstill owing to the divergent wavelength and the vanishing group velocity, effectively rendering, through nonlinearity, a positive-epsilon trapping cavity carved in an otherwise slightly-negative-epsilon medium. By numerically solving Maxwell's equations, we find a soliton-like family of still azimuthal doughnuts, which we further study through an adiabatic perturbative theory that describes soliton evaporation in lossy media or condensation in actively pumped materials. Our results suggest applications in optical data processing and storage, quantum optical memories, and soliton-based lasers without cavities. Additionally, near-zero-index conditions can also be found in the interplanetary medium and in the atmosphere, where we provide an alternative explanation to the rare phenomenon of ball-lightning. △ Less

Submitted 15 July, 2015; originally announced July 2015.

Unlocking the full potential of wave-matter nonlinear coupling in the epsilon-near-zero regime

Authors: Alessandro Ciattoni, Carlo Rizza, Andrea Marini, Andrea Di Falco, Daniele Faccio, Michael Scalora

Abstract: In recent years, unconventional metamaterial properties have triggered a revolution of electromagnetic research which has unveiled novel scenarios of wave-matter interaction. A very small dielectric permittivity is a leading example of such unusual features, since it produces an exotic static-like regime where the electromagnetic field is spatially slowly-varying over a physically large region. Th… ▽ More In recent years, unconventional metamaterial properties have triggered a revolution of electromagnetic research which has unveiled novel scenarios of wave-matter interaction. A very small dielectric permittivity is a leading example of such unusual features, since it produces an exotic static-like regime where the electromagnetic field is spatially slowly-varying over a physically large region. The so-called epsilon-near-zero metamaterials thus offer an ideal platform where to manipulate the inner details of the "stretched" field. Here we theoretically prove that a standard nonlinearity is able to operate such a manipulation to the point that even a thin slab produces a dramatic nonlinear pulse transformation, if the dielectric permittivity is very small within the field bandwidth. The predicted non-resonant releasing of full nonlinear coupling produced by the epsilon-near-zero condition does not resort to any field enhancement mechanisms and opens novel routes to exploiting matter nonlinearity for steering the radiation by means of ultra-compact structures. △ Less

Submitted 10 July, 2015; originally announced July 2015.

Comments: 8 pages, 4 figures