arXiv subjects

Pierre-Louis de Assis

Publications and source records attributed to Pierre-Louis de Assis.

12 recordsLinked to original sources

arXiv2026

Cryogenic Graphene-Based Phase Modulators for Quantum Information Processing

Electro-optic modulators are key components for photonic quantum computing, particularly in fully cryovenic integrated platforms where low loss and compactness are critical. We present a systematic theoretical investigation of compact dual-layer graphene (DSLG) electro-optic phase modulators integrated on silicon nitride waveguides, with emphasis on cryogenic operation. By combining electromagnetic simulations with a physically consistent description of graphene conductivity based on the Kybo formalism, we analyze the interplay between electrostatic tuning, optical mode confinement, and material-dependent losses. We show that cryogenic operation enhances device performance by sharpening the Fermi-Dirac distribution, enabling access to the Pauli-blocking regime at lower Fermi levels and reducing the required modulation length. Through optimization of the waveguide geometry, dielectric spacer thickness and permittivity, and graphene quality, we identify regimes that simultaneously minimize insertion loss and device footprint under realistic voltage constraints. The optimized designs achieve near-pure phase modulation with insertion losses below 0.3 dB and modulation lengths below 50 um at 10 K, while maintaining GHz-scale bandwidths. These results provide quantitative design guidelines for low-loss, compact, cryogenic graphene phase modulators for scalable integrated quantum photonics.

physics.optics↗

arXiv2026

Estimating the electrical energy cost of performing arbitrary state preparation using qubits and qudits in integrated photonic circuits

As quantum photonic hardware scales toward computationally relevant sizes, energy consumption has emerged as a key constraint. Programmable photonic integrated circuits, composed of interferometer meshes with tunable phase modulators, provide a flexible platform for quantum information processing using both qubits and qudits. In this work, we analyze the energetic cost of such devices by focusing on arbitrary quantum state preparation, a resource-intensive task central to quantum simulation and information processing. Using a common hardware, we benchmark qudit-based implementations, gate-based quantum computation, and measurement-based quantum computation. We find that while qudit encodings are attractive at small scale, their footprint and reconfiguration costs grow rapidly with system size, whereas qubit-based approaches incur significant overhead from entangling operations, feedforward, and reprogramming. Across all paradigms, scaling beyond a few tens of qubits renders either the energy consumption or the total preparation time prohibitive on fully programmable PICs. Our results highlight the need for optimized, task-specific photonic architectures to enable energy-efficient scaling.

quant-ph↗

arXiv2025

1T'-MoTe$_2$ as an integrated saturable absorber for photonic machine learning

We investigate the saturable absorption behavior of a 1T'-MoTe$_2$ monolayer integrated with a silicon nitride waveguide for applications in photonic neural networks. Using experimental transmission measurements and theoretical modeling, we characterize the nonlinear response of the material. Our model, incorporating quasi-Fermi level separation and carrier dynamics, successfully explains these behaviors and predicts the material's absorption dependence on the carrier density. Furthermore, we demonstrate a coupling efficiency of up to 20% between the 1T'-MoTe$_2$ monolayer and the silicon nitride waveguide, with saturation achievable at input powers as low as a few uW. These results suggest that 1T'-MoTe$_2$ is a promising candidate for implementing nonlinear functions in integrated photonic neural networks.

physics.optics↗

arXiv2025

Hybrid integration of two-dimensional dichalcogenides for low power saturable absorption in photonic integrated circuits

Silicon photonics provides a versatile platform for large-scale integration of optical functions, but its weak intrinsic nonlinear response limits the realization of active, intensity-dependent functionalities. Hybrid integration of two-dimensional (2D) materials has emerged as a promising strategy to overcome these limitations by enabling strong light--matter interaction and broadband absorption. Here, we demonstrate saturable absorption in a Complementary Metal-Oxide-Semiconductor (CMOS)-compatible silicon-on-insulator (SOI) microring resonator integrated with an exfoliated monolayer of 1T'-MoTe2. Transmission measurements under varying input powers reveal a clear nonlinear absorption response, with a saturation power as low as 2(1)uW. A phenomenological model accurately reproduces the experimental results, confirming the nonlinear behavior induced by the hybrid MoTe2 integration. These findings establish a proof-of-concept for ultracompact, low-power saturable absorbers in photonic integrated circuits (PICs), paving the way for applications in integrated lasers, ultrafast optical signal processing, and neuromorphic photonics.

physics.optics↗

arXiv2025

Broadband photonic structures to achieve high coupling efficiencies and Purcell factors with dark and interlayer excitons in 2D materials

Horizontal slot waveguides are planar photonic structures with a guided mode which is strongly polarized in the out-of-plane direction and tightly confined in a sub-wavelength region of lower refractive index. We show through FDTD simulations that this mode can lead to coupling efficiencies $β>80\%$ and Purcell factors $F_P>10$ for some types of dark intralayer excitons in transition metal dichalcogenide (TMD) monolayers -- more aplty named ``gray excitons'', as their out-of-plane dipole does couple to adequately polarized light -- as well as interlayer excitons in TMD heterostructures. These figures indicate a path to the strong coupling regime for gray and interlayer excitons, while bright excitons are poorly coupled to the slot mode and experience Purcell suppression for $λ>\SI{1}{\micro\meter}$. A significant hurdle towards strong coupling, however, is the low oscillator strengths of these two excitonic species. We use the Tavis-Cummings model to show that a horizontal-slot racetrack resonator can overcome this difficulty and reach a cooperativity $C>>1$, albeit sacrificing the broadband characteristic of waveguides.

quant-ph↗

arXiv2021

Accurate modeling and characterization of photothermal forces in optomechanics

Photothermal effects have been pointed out as prominent sources of forces in optomechanical systems, competing with the standard radiation pressure interactions. In this Article, we derive a novel and accurate model for the prediction of photothermal forces and establish how some previous proposals can be complemented to yield precise results. As a proof-of-concept, we perform numerical and experimental tests on GaAs microdisks cavities and obtain striking agreement with our framework, revealing the importance of considering surface photothermal forces and the effects of multiple thermal modes in microphotonic devices.

physics.optics↗

arXiv2021

Inducing micromechanical motion by optical excitation of a single quantum dot

Hybrid quantum optomechanical systems offer an interface between a single two-level system and a macroscopical mechanical degree of freedom. In this work, we build a hybrid system made of a vibrating microwire coupled to a single semiconductor quantum dot (QD) via material strain. It was shown a few years ago, that the QD excitonic transition energy can thus be modulated by the microwire motion. We demonstrate here the reverse effect, whereby the wire is set in motion by the resonant drive of a single QD exciton with a laser modulated at the mechanical frequency. The resulting driving force is found to be almost 3 orders of magnitude larger than radiation pressure. From a fundamental aspect, this state dependent force offers a convenient strategy to map the QD quantum state onto a mechanical degree of freedom.

cond-mat.mes-hall↗

arXiv2018

Optical force laws for guided light in linear media

The mechanical response of transparent materials to optical forces is a topic that concerns a wide range of fields, from the manipulation of biological material by optical tweezers to the design of nano-optomechanical systems (NOMS). However, the fundamental aspects of such forces have always been surrounded by controversies, and several different formulations have been proposed. In this work, we focus on the specific case of light propagating as a superposition of guided modes in lossless dielectric waveguides as a physical example upon which to build a general stress tensor. We use this formalism to calculate optical forces for straight and curved waveguide sections and all possible excitation configurations for a given set of coupled eigenmodes, and then compare the results for each of the known proposed optical force laws as well as a novel one derived from this general stress tensor. We show that proper use of the divergence theorem is crucial to account for all force terms, many of which vanish if the procedure most commonly used is applied for situations other than eigenmodes in straight waveguides. A better understanding of how different stress tensors predict very different forces for certain waveguide geometries opens a pathway for new experimental tests of each formulation.

physics.optics↗

arXiv2017

Center of mass acceleration in coupled nanowaveguides due to transverse optical beating force

Eigenmode optical forces arising in symmetrically coupled waveguides have opposite sign on opposite waveguides and thus can deform the waveguides by changing their relative separation, but cannot change any other degree of freedom on their own. It would be extremely desirable to have a way to act on the center of mass of such a system. In this work we show that it is possible to do so by injecting a superposition of eigenmodes that are degenerate in frequency and have opposite parity along the desired direction, resulting in beating forces that have the same sign on opposite waveguides and therefore act on the center of mass. We have used both the Maxwell Stress Tensor formalism and the induced dipole force equation to numerically calculate this transverse beating force and have found its magnitude to be comparable to the eigenmode forces. We also show that the longitudinal variation caused by the spatial beating pattern on the time-averaged quantities used in the calculations must be taken into account in order to properly employ the divergence theorem and obtain the correct magnitudes. We then propose a heuristic model that shows good quantitative agreement with the numerical results and may be used as a prototyping tool for accurate and fast computation without relying on expensive numerical computation.

physics.optics↗

arXiv2013

Strain-mediated coupling in a quantum dot-mechanical oscillator hybrid system

Recent progress in nanotechnology has allowed to fabricate new hybrid systems where a single two-level system is coupled to a mechanical nanoresonator. In such systems the quantum nature of a macroscopic degree of freedom can be revealed and manipulated. This opens up appealing perspectives for quantum information technologies, and for the exploration of quantum-classical boundary. Here we present the experimental realization of a monolithic solid-state hybrid system governed by material strain: a quantum dot is embedded within a nanowire featuring discrete mechanical resonances corresponding to flexural vibration modes. Mechanical vibrations result in a time-varying strain field that modulates the quantum dot transition energy. This approach simultaneously offers a large light extraction efficiency and a large exciton-phonon coupling strength $g_0$. By means of optical and mechanical spectroscopy, we find that $g_0/2π$ is nearly as large as the mechanical frequency, a criterion which defines the ultra-strong coupling regime.

cond-mat.mes-hall↗

arXiv2013

Experimental Test of the Quantum Violation of the Noncontextuality Inequalities for the n-Cycle Scenario

The inequalities that separate contextual from noncontextual correlations for the n-cycle scenario (consisting of n dichotomic observables Oj, with j = 0, ..., n-1 and such that Oj and Oj+1 are jointly measurable) have been recently identified [arXiv:1206.3212 (2012)]. Here we report the results of an experiment designed to reach the maximum quantum violation of these inequalities for any even number of observables ranging from 4 to 14. The four dimensional Hilbert space required for the test was spanned by two photonic qubits encoded in the transversal path of photon pairs, and the joint measurability of the observables is guaranteed by measuring correlations between observables from different modes. Our results show contextual correlations as predicted by quantum mechanics.

quant-ph↗

arXiv2011

Testing sequential quantum measurements: how can maximal knowledge be extracted?

The extraction of information from a quantum system unavoidably implies a modification of the measured system itself. It has been demonstrated recently that partial measurements can be carried out in order to extract only a portion of the information encoded in a quantum system, at the cost of inducing a limited amount of disturbance. Here we analyze experimentally the dynamics of sequential partial measurements carried out on a quantum system, focusing on the trade-off between the maximal information extractable and the disturbance. In particular we consider two different regimes of measurement, demonstrating that, by exploiting an adaptive strategy, an optimal trade-off between the two quantities can be found, as observed in a single measurement process. Such experimental result, achieved for two sequential measurements, can be extended to N measurement processes.

quant-ph↗