arXiv subjects

Christophe Sauvan

Publications and source records attributed to Christophe Sauvan.

7 recordsLinked to original sources

arXiv2023

Systematic design of a robust half-W1 photonic crystal waveguide for interfacing slow light and trapped cold atoms

Novel platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms in single pass, with applications to quantum non-linear optics and quantum simulation. A strong challenge for the experimental development of this emerging waveguide-QED field of research is to combine facilitated optical access for atom transport, atom trapping via guided modes and robustness to inherent nanofabrication imperfections. In this endeavor, here we propose to interface Rubidium atoms with a photonic-crystal waveguide based on a large-index GaInP slab. With a specifically tailored half-W1 design, we show that a large chiral coupling to the waveguide can be obtained and guided modes can be used to form two-color dipole traps for atoms at 116~nm from the edge of the structure. This optimized device should greatly improve the level of experimental control and facilitate the atom integration.

quant-ph↗

arXiv2022

Asymmetric comb waveguide for strong interactions between atoms and light

Coupling quantum emitters and nanostructures, in particular cold atoms and waveguides, has recently raised a large interest due to unprecedented possibilities of engineering light-matter interactions. However, the implementation of these promising concepts has been hampered by various theoretical and experimental issues. In this work, we propose a new type of periodic dielectric waveguide that provides strong interactions between atoms and guided photons with an unusual dispersion. We design an asymmetric comb waveguide that supports a slow mode with a quartic (instead of quadratic) dispersion and an electric field that extends far into the air cladding for an optimal interaction with atoms. We compute the optical trapping potential formed with two guided modes at frequencies detuned from the atomic transition. We show that cold Rubidium atoms can be trapped as close as 100 nm from the structure in a 1.3-mK-deep potential well. For atoms trapped at this position, the emission into guided photons is largely favored, with a beta factor as high as 0.88 and a radiative decay rate into the slow mode 10 times larger than the free-space decay rate.

quant-ph↗

arXiv2021

Quasinormal modes expansions for nanoresonators made of absorbing dielectric materials: study of the role of static modes

The interaction of light with photonic resonators is determined by the eigenmodes of the system. Modal theories based on quasinormal modes provide a natural tool to calculate and understand light scattering by nanoresonators. We show that, in the case of resonators made of absorbing dielectric materials, eigenmodes with zero eigenfrequency (static modes) play a key role in the modal formalism. The excitation of static modes builds a non-resonant contribution to the modal expansion of the scattered field. This non-resonant term plays a crucial physical role since it largely contributes to the off-resonance signal to which resonances are added in amplitude, possibly leading to interference phenomena and Fano resonances. By considering light scattering by a silicon nanosphere, we quantify the impact of static modes. This study shows that the importance of static modes is not just formal. Modal expansions without static modes reconstruct an incorrect internal field and incorrect extinction and absorption cross-sections. Static modes are of prime importance in an expansion truncated to only a few modes.

physics.optics↗

arXiv2020

Upper bound for light absorption assisted by a nanoantenna

We study light absorption by a dipolar absorber in a given environment, which can be a nanoantenna or any complex inhomogeneous medium. From first-principle calculations, we derive an upper bound for the absorption, which decouples the impact of the environment from the one of the absorber. Since it is an intrinsic characteristic of the environment regardless of the absorber, it provides a good figure of merit to compare the ability of different systems to enhance absorption. We show that, in the scalar approximation, the relevant parameter is not the field enhancement but the ratio between the field enhancement and the local density of states. Consequently, a plasmonic structure supporting hot spots is not necessarily the best choice to enhance absorption. We also show that our theoretical results can be applied beyond the scalar approximation and the plane-wave illumination.

physics.optics↗

arXiv2019

Bound states in the continuum in symmetric and asymmetric photonic crystal slabs

We develop a semi-analytical model to describe bound states in the continuum (BICs) in photonic crystal slabs. We model leaky modes supported by photonic crystal slabs as a transverse Fabry-Perot resonance composed of a few propagative Bloch waves bouncing back and forth vertically inside the slab. This multimode Fabry-Perot model accurately predicts the existence of BICs and their positions in the parameter space. We show that, regardless of the slab thickness, BICs cannot exist below a cut-off frequency, which is related to the existence of the second-order Bloch wave in the photonic crystal. Thanks to the semi-analyticity of the model, we investigate the dynamics of BICs with the slab thickness in symmetric and asymmetric photonic crystal slabs. We evidence that the symmetry-protected BICs that exist in symmetric structures at the Γ-point of the dispersion diagram can still exist when the horizontal mirror symmetry is broken, but only for particular values of the slab thickness.

physics.optics↗

arXiv2018

Light interaction with photonic and plasmonic resonances

In this Review, the theory and applications of optical micro and nanoresonators are presented from the underlying concept of their natural resonances, the so-called quasi-normal modes (QNMs). The latter are the basic constituents governing the response of resonators. Characterized by complex frequencies, QNMs are initially loaded by a driving field and then decay exponentially in time due to power leakage or absorption. Here, the use of QNM-expansion formalisms to model these basic effects is explored. Such modal expansions that operate at complex frequencies distinguish from the current user habits in electromagnetic modeling, which rely on classical Maxwell equation solvers operating at real frequencies or in the time domain; they also bring much deeper physical insight into the analysis. An extensive overview of the historical background on QNMs in electromagnetism and a detailed discussion of recent relevant theoretical and numerical advances are therefore presented. Additionally, a concise description of the role of QNMs on a number of examples involving electromagnetic resonant fields and matter, including the interaction between quantum emitters and resonators (Purcell effect, weak and strong coupling, superradiance...), Fano interferences, the perturbation of resonance modes, and light transport and localization in disordered media is provided.

physics.optics↗

arXiv2015

Polaritonic modes in a dense cloud of atoms

We analyze resonant light scattering by an atomic cloud in a regime where near-field interactions between scatterers cannot be neglected. We first use a microscopic approach and calculate numerically the eigenmodes of the cloud for many different realizations. It is found that there always exists a small number of polaritonic modes that are spatially coherent and superradiant. We show that scattering is always dominated by these modes. We then use a macroscopic approach by introducing an effective permittivity so that the atomic cloud is equivalent to a dielectric particle. We show that there is a one-to-one correspondence between the microscopic polaritonic modes and the modes of a homogeneous particle with an effective permittivity.

physics.atom-ph↗