SearcharxivSearch

arXiv subjects

Philippe W. Courteille

Publications and source records attributed to Philippe W. Courteille.

At least 19 recordsLinked to original sources

Cooperative atomic emission from a line of atoms interacting with a resonant plane surface

Cooperative effects such as super- and subradiance can be observed in the fluorescence emitted by a system of N atoms in vacuum, after interaction with a laser beam. In the vicinity of a dielectric or metallic surface, Casimir-Polder effects can modify collective atomic frequency shifts and decay rates. In this work, we study cooperative fluorescent emission next to resonant surfaces using the coupled dipoles model. We show that cooperative effects, expected in free space, are absent when the atoms are close to a surface whose polariton resonances coincide with the dominant atomic dipole coupling. In this case, cooperative effects are overshadowed by the very fast decay of the atomic fluorescence into surface modes. We illustrate our formalism and our results by considering a line of cesium 6D3/2 atoms in front of a sapphire surface. Finally, we propose the study of Cesium 6P3/2 atoms in front of a resonant metasurface as the most promising scenario for experimentally demonstrating the results of our study.

quant-ph

Symmetry breaking and non-ergodicity in a driven-dissipative ensemble of multi-level atoms in a cavity

Dissipative light-matter systems can display emergent collective behavior. Here, we report a $\mathbb{Z}_2$-symmetry-breaking phase transition in a system of multi-level $^{87}$Rb atoms strongly coupled to a weakly driven two-mode optical cavity. In the symmetry-broken phase, non-ergodic dynamics manifests in the emergence of multiple stationary states with disjoint basins of attraction. This feature enables the amplification of a small atomic population imbalance into a characteristic macroscopic cavity transmission signal. Our experiment does not only showcase strongly dissipative atom-cavity systems as platforms for probing non-trivial collective many-body phenomena, but also highlights their potential for hosting technological applications in the context of sensing, density classification, and pattern retrieval dynamics within associative memories.

quant-ph

Quantum resonant optical bistability with a narrow atomic transition: bistability phase diagram in the bad cavity regime

We report on the observation of a novel manifestation of saturation-induced optical bistability in a resonantly pumped optical ring cavity interacting strongly with a cloud of atoms via a narrow atomic transition. The bistability emerges, above a critical pump rate, as an additional peak in the cavity's normal mode spectrum close to atomic resonance. This third transmission peak is usually suppressed due to strong resonant absorption, but in our experiment it is visible because of the linewidth of the atomic transition being much smaller than that of the cavity, which sets the experiment into the bad-cavity regime. Relying on complete saturation of the transition, this bistability has a quantum origin and cannot be mimicked by a classical material presenting a nonlinear refraction index. The appearance of the central peak in addition to the normal modes is predicted by a semi-classical model derived from the Tavis-Cummings Hamiltonian from which we derive a bistability phase diagram that connects our observations with former work on optical bistability in the good cavity regime. The phase diagram reveals several so far unexplored bistable phases.

quant-ph

Collective atom-cavity coupling and non-linear dynamics with atoms with multilevel ground states

We investigate experimentally and theoretically the collective coupling between atoms with multilevel ground state manifolds and an optical cavity mode. In our setup the cavity field optically pumps populations among the ground states. The ensuing dynamics can be conveniently described by means of an effective dynamical atom-cavity coupling strength that depends on the occupation of the individual states and their coupling strengths with the cavity mode. This leads to a dynamical backaction of the atomic populations on the atom-cavity coupling strength which results in a non-exponential relaxation dynamics. We experimentally observe this effect with laser-cooled $^{87}$Rb atoms, for which we monitor the collective normal-mode splitting in real time. Our results show that the multilevel structure of electronic ground states can significantly alter the relaxation behavior in atom-cavity settings as compared to ensembles of two-level atoms.

quant-ph

Hollow Bessel beams for guiding atoms between vacuum chambers: A proposal and efficiency study

We explore a scheme for guiding cold atoms through a hollow Bessel beam generated by a single axicon and a lens from a 2D magneto-optical trap toward a science chamber. We compare the Bessel beam profiles measured along the optical axis to a numerical propagation of the beam's wavefront, and we show how it is affected by diffraction during the passage through a long narrow funnel serving as a differential pumping tube between the chambers. We derive an approximate analytic expression for the intensity distribution of the Bessel beam and the dipolar optical force acting on the atoms. By a Monte-Carlo simulation based on a stochastic Runge-Kutta algorithm of the motion of atoms initially prepared at a given temperature we show that a considerable enhancement of the transfer efficiency can be expected in the presence of a sufficiently intense Bessel beam.

physics.atom-ph

Controlling photon bunching and antibunching of two quantum emitters near a core-shell sphere

The collective spontaneous emission of two point-dipole emitters near a plasmonic core-shell nanosphere is theoretically investigated. Based on the expansion of mode functions in vector spherical harmonics, we derive closed analytical expressions for both the cooperative decay rate and the dipole-dipole interaction strength associated with two point dipoles close to a sphere. Considering a plasmonic nanoshell containing a linearly amplifying medium inside the core, the second-order correlation function for the two emitters shows that it is possible to tune the photon emission, selecting either photon bunching or antibunching as a function of the polarization and position of the sphere. This result opens vistas to applications involving tunable single-photon sources in engineered artificial media.

physics.optics

Tunable Fano resonances in the decay rates of a pointlike emitter near a graphene-coated nanowire

Based on the Lorenz-Mie theory, we derive analytical expressions of radiative and nonradiative transition rates for different orientations of a point dipole emitter in the vicinity of an infinitely long circular cylinder of arbitrary radius. Special attention is devoted to the spontaneous decay rate of a dipole emitter near a subwavelength-diameter nanowire coated with a graphene monolayer. We show that plasmonic Fano resonances associated with light scattering by graphene-coated nanowires appear in the Purcell factor as a function of transition wavelength. Furthermore, the Fano line shape of transition rates can be tailored and electrically tuned by varying the distance between emitter and cylinder and by modulating the graphene chemical potential, where the Fano asymmetry parameter is proportional to the square root of the chemical potential. This gate-voltage-tunable Fano resonance leads to a resonant enhancement and suppression of light emission in the far-infrared range of frequencies. This result could be explored in applications involving ultrahigh-contrast switching for spontaneous emission in specifically designed tunable plasmonic nanostructures.

physics.optics

Photon-antibunching in the fluorescence of statistical ensembles of emitters at an optical nanofiber-tip

This proposal investigates the photon-statistics of light emitted by a statistical ensemble of cold atoms excited by the near-field of an optical nanofiber tip. Dipole-dipole interactions of atoms at such short distance from each other suppress the simultaneous emission of more than one photon and lead to antibunching of photons. We consider a mean atom number on the order of one and deal with a poissonian mixture of one and two atoms including dipole-dipole interactions and collective decay. Time tracks of the atomic states are simulated in quantum Monte Carlo simulations from which the $g^{(2)}$-photon autocorrelation function is derived. The general results can be applied to any statistical ensemble of emitters that are interacting by dipole-dipole interactions.

quant-ph

Fano resonances in plasmonic core-shell particles and the Purcell effect

Despite a long history, light scattering by particles with size comparable with the light wavelength still unveils surprising optical phenomena, and many of them are related to the Fano effect. Originally described in the context of atomic physics, the Fano resonance in light scattering arises from the interference between a narrow subradiant mode and a spectrally broad radiation line. Here, we present an overview of Fano resonances in coated spherical scatterers within the framework of the Lorenz-Mie theory. We briefly introduce the concept of conventional and unconventional Fano resonances in light scattering. These resonances are associated with the interference between electromagnetic modes excited in the particle with different or the same multipole moment, respectively. In addition, we investigate the modification of the spontaneous-emission rate of an optical emitter at the presence of a plasmonic nanoshell. This modification of decay rate due to electromagnetic environment is referred to as the Purcell effect. We analytically show that the Purcell factor related to a dipole emitter oriented orthogonal or tangential to the spherical surface can exhibit Fano or Lorentzian line shapes in the near field, respectively.

physics.optics

Fano resonances and fluorescence enhancement of a dipole emitter near a plasmonic nanoshell

We analytically study the spontaneous emission of a single optical dipole emitter in the vicinity of a plasmonic nanoshell, based on the Lorenz-Mie theory. We show that the fluorescence enhancement due to the coupling between optical emitter and sphere can be tuned by the aspect ratio of the core-shell nanosphere and by the distance between the quantum emitter and its surface. In particular, we demonstrate that both the enhancement and quenching of the fluorescence intensity are associated with plasmonic Fano resonances induced by near- and far-field interactions. These Fano resonances have asymmetry parameters whose signs depend on the orientation of the dipole with respect to the spherical nanoshell. We also show that if the atomic dipole is oriented tangentially to the nanoshell, the interaction exhibits saddle points in the near-field energy flow. This results in a Lorentzian fluorescence enhancement response in the near field and a Fano line-shape in the far field. The signatures of this interaction may have interesting applications for sensing the presence and the orientation of optical emitters in close proximity to plasmonic nanoshells.

physics.optics

Collective strong coupling of cold potassium atoms in a ring cavity

We present experiments on ensemble cavity quantum electrodynamics with cold potassium atoms in a high-finesse ring cavity. Potassium-39 atoms are cooled in a two-dimensional magneto-optical trap and transferred to a three-dimensional trap which intersects the cavity mode. The apparatus is described in detail and the first observations of strong coupling with potassium atoms are presented. Collective strong coupling of atoms and light is demonstrated via the splitting of the cavity transmission spectrum and the avoided crossing of the normal modes.

physics.atom-ph

Spatial and temporal localization of light in two dimensions

Quasi-resonant scattering of light in two dimensions can be described either as a scalar or as a vectorial electromagnetic wave. Performing a scaling analysis we observe in both cases long lived modes, yet only the scalar case exhibits Anderson localized modes together with extremely long mode lifetimes. We show that the localization length of these modes is influenced only by their position, and not their lifetime. Investigating the reasons for the absence of localization, it appears that both the coupling of several polarizations and the presence of near-field terms are able to prevent long lifetimes and Anderson localization.

physics.optics

Synchronization of Bloch oscillations by a ring cavity

We consider Bloch oscillations of ultracold atoms stored in a one-dimensional vertical optical lattice and simultaneously interacting with a unidirectionally pumped optical ring cavity whose vertical arm is collinear with the optical lattice. We find that the feedback provided by the cavity field on the atomic motion synchronizes Bloch oscillations via a mode-locking mechanism, steering the atoms to the lowest Bloch band. It also stabilizes Bloch oscillations against noise, and even suppresses dephasing due to atom-atom interactions. Furthermore, it generates periodic bursts of light emitted into the counter-propagating cavity mode, providing a non-destructive monitor of the atomic dynamics. All these features may be crucial for future improvements of the design of atomic gravimeters based on recording Bloch oscillations.

cond-mat.quant-gas

Coherence effects in scattering order expansion of light by atomic clouds

We interpret cooperative scattering by a collection of cold atoms as a multiple scattering process. Starting from microscopic equations describing the response of $N$ atoms to a probe light beam, we represent the total scattered field as an infinite series of multiple scattering events. As an application of the method, we obtain analytical expressions of the coherent intensity in the double scattering approximation for Gaussian density profiles. In particular, we quantify the contributions of coherent backward and forward scattering.

physics.optics

Interplay between radiation pressure force and scattered light intensity in the cooperative scattering by cold atoms

The interplay between the superradiant emission of a cloud of cold two-level atoms and the radiation pressure force is discussed. Using a microscopic model of coupled atomic dipoles driven by an external laser, the radiation field and the average radiation pressure force are derived. A relation between the far-field scattered intensity and the force is derived, using the optical theorem. Finally, the scaling of the sample scattering cross section with the parameters of the system is studied.

physics.atom-ph

The role of Mie scattering in the seeding of matter-wave superradiance

Matter-wave superradiance is based on the interplay between ultracold atoms coherently organized in momentum space and a backscattered wave. Here, we show that this mechanism may be triggered by Mie scattering from the atomic cloud. We show how the laser light populates the modes of the cloud, and thus imprints a phase gradient on the excited atomic dipoles. The interference with the atoms in the ground state results in a grating, that in turn generates coherent emission, contributing to the backward light wave onset. The atomic recoil 'halos' created by the scattered light exhibit a strong anisotropy, in contrast to single-atom scattering.

physics.atom-ph

Optical parametric oscillation with distributed feedback in cold atoms

There is currently a strong interest in mirrorless lasing systems, in which the electromagnetic feedback is provided either by disorder (multiple scattering in the gain medium) or by order (multiple Bragg reflection). These mechanisms correspond, respectively, to random lasers and photonic crystal lasers. The crossover regime between order and disorder, or correlated disorder, has also been investigated with some success. Here, we report one-dimensional photonic-crystal lasing (that is, distributed feedback lasing) with a cold atom cloud that simultaneously provides both gain and feedback. The atoms are trapped in a one-dimensional lattice, producing a density modulation that creates a strong Bragg reflection with a small angle of incidence. Pumping the atoms with auxiliary beams induces four-wave mixing, which provides parametric gain. The combination of both ingredients generates a mirrorless parametric oscillation with a conical output emission, the apex angle of which is tunable with the lattice periodicity.

physics.atom-ph

Photonic Band Gaps in One-Dimensionally Ordered Cold Atomic Vapors

We experimentally investigate the Bragg reflection of light at one-dimensionally ordered atomic structures by using cold atoms trapped in a laser standing wave. By a fine tuning of the periodicity, we reach the regime of multiple reflection due to the refractive index contrast between layers, yielding an unprecedented high reflectance efficiency of 80%. This result is explained by the occurrence of a photonic band gap in such systems, in accordance with previous predictions.

physics.atom-ph