arXiv subjects

Guillaume Labeyrie

Publications and source records attributed to Guillaume Labeyrie.

At least 19 recordsLinked to original sources

arXiv2023

Analysing spatiotemporal instabilities in magneto-optical traps with the tools of turbulence theory

A large cloud of $^{87}$Rb atoms confined in a magneto-optical trap exhibits, in a certain regime of parameters, spatio-temporal instabilities with a dynamics resembling that of a turbulent fluid. We apply the methods of turbulence theory based on structure function analysis to extract scaling exponents which are compared to known turbulent regimes. This analysis also allows us to make a clear distinction between different instability regimes.

physics.atom-ph↗

arXiv2023

Intensity Interferometry observations of the H$\alpha$ envelope of $\gamma$ Cas with M\'{e}O and a portable telescope

We report on observations of the extended environment of the bright Be star $\gamma$-Cas performed using intensity interferometry measurements within its H$\alpha$ emission line. These observations were performed using a modified version of the I2C intensity interferometry instrument installed onto the 1.54 meter M\'{e}O optical metrology telescope and a portable 1-meter telescope (T1M). In order to better constrain the extent of the H$\alpha$ envelope, observations were performed for two different positions of the T1M telescope, corresponding to an intermediate and long baselines in which the extended region was partially and fully resolved. We find that the observed data are consistent with past interferometric observations of $\gamma$-Cas. These observations demonstrate the capability to equip optical telescopes of different optical designs with intensity interferometry capabilities and illustrate the potential to scale a similar system onto many additional telescopes.

astro-ph.IM↗

arXiv2022

Nonequilibrium steady state in a large magneto-optical trap

Considering light-mediated long-range interactions between cold atoms in a magneto-optical trap (MOT), we present numerical evidence of a nonequilibrium steady state (NESS) for sufficiently large number of atoms (> 10^8). This state manifests itself as the appearance of an anisotropic distribution of velocity when a MOT approaches the threshold beyond which self-oscillating instabilities occur. Our three-dimensional (3D) spatiotemporal model with nonlocal spatial dependencies stemming from the interatomic interactions has recently been compared successfully to predict different instability thresholds and regimes in experiments with rubidium atoms. The behavior of the NESS is studied as a function of the main MOT parameters, including its spatiotemporal characteristics.

physics.atom-ph↗

arXiv2022

Field and intensity correlations: the Siegert relation from stars to quantum emitters

The Siegert relation relates field and intensity temporal correlations. After a historical review of the Siegert relation and the Hanbury Brown and Twiss effect, we discuss the validity of this relation in two different domains. We first show that this relation can be used in astrophysics to determine the fundamental parameters of stars, and that it is especially important for the observation with stellar emission lines. Second, we verify the validity of this relation for moving quantum scatterers illuminated by a strong driving field.

physics.atom-ph↗

arXiv2022

Intensity Interferometry at Calern and beyond: progress report

We present the current status of the I2C stellar intensity interferometer used towards high angular resolution observations of stars in visible wavelengths. In these proceedings, we present recent technical improvements to the instrument, and share results from ongoing campaigns using arrays of small diameter optical telescopes. A tip-tilt adaptive optics unit was integrated into the optical system to stabilize light injection into an optical fiber. The setup was successfully tested with several facilities on the Calern Plateau site of the Observatoire de la Côte d'Azur. These include one of the 1 m diameter telescopes of the C2PU observatory, a portable 1 m diameter telescope, and also the 1.5 m MéO telescope. To better constrain on-sky measurements, the spectral transmission of instrument was characterized in the laboratory using a high resolution spectrograph. The system was also tested with two of the auxiliary telescopes of the VLTI resulting in successful temporal and spatial correlation measurements of three stars.

astro-ph.IM↗

arXiv2022

Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel

In this paper we report on spatial intensity interferometry measurements within the H$α$ line on two stars: the Luminous Blue Variable supergiant \PCygni\,and the late-type B supergiant Rigel. The experimental setup was upgraded to allow simultaneous measurement of two polarization channels, instead of one in our previous setup, and the zero baseline correlation function on-sky to validate independent estimates obtained from the stellar spectrum and the instrumental spectral throughput. Combined with simultaneous spectra measurements and based on radiative transfer models calculated with the code CMFGEN, we were able to fit our measured visibility curves to extract the stellar distances. Our distance determinations for both \PCygni\ (1.61 $\pm$ 0.18 kpc) and Rigel (0.26 $\pm$ 0.02 kpc) agree very well with the values provided by astrometry with the Gaia and Hipparcos missions, respectively. This result for Rigel was obtained by adopting a stellar luminosity of $L_{\star}$ = 123000 $L_{\odot}$, which is reported in the literature as being consistent with the Hipparcos distance to Rigel. However, due to the lack of consensus on Rigel's luminosity, we also explore how the adoption of the stellar luminosity in our models affects our distance determination for Rigel. In conclusion, we support, in an independent way, the distance to Rigel as the one provided by the Hipparcos mission, when taking the luminosity of 123000 $L_{\odot}$ at face value. This study is the first successful step towards extending the application of the Wind Momentum Luminosity Relation method for distance calibration from an LBV supergiant to a more normal late-type B supergiant.

astro-ph.SR↗

arXiv2021

Self-Organization in Cold Atoms Mediated by Diffractive Coupling

This article discusses self-organization in cold atoms via light-mediated interactions induced by feedback from a single retro-reflecting mirror. Diffractive dephasing between the pump beam and the spontaneous sidebands selects the lattice period. Spontaneous breaking of the rotational and translational symmetry occur in the 2D plane transverse to the pump. We elucidate how diffractive ripples couple sites on the self-induced atomic lattice. The nonlinear phase shift of the atomic cloud imprinted onto the optical beam is the parameter determining coupling strength. The interaction can be tailored to operate either on external degrees of freedom leading to atomic crystallization for thermal atoms and supersolids for a quantum degenerate gas, or on internal degrees of freedom like populations of the excited state or Zeeman sublevels. Using the light polarization degrees of freedom on the Poincar{é} sphere (helicity and polarization direction), specific irreducible tensor components of the atomic Zeeman states can be coupled leading to spontaneous magnetic ordering of states of dipolar and quadrupolar nature. The requirements for critical interaction strength are compared for the different situations. Connections and extensions to longitudinally pumped cavities, counterpropagating beam schemes and the CARL instability are discussed.

nlin.PS↗

arXiv2021

I3T: Intensity Interferometry Imaging Telescope

We propose a new approach, based on the Hanbury Brown and Twiss intensity interferometry, to transform a Cherenkov telescope to its equivalent optical telescope. We show that, based on the use of photonics components borrowed from quantum-optical applications, we can recover spatial details of the observed source down to the diffraction limit of the Cherenkov telescope, set by its diameter at the mean wavelength of observation. For this, we propose to apply aperture synthesis techniques from pairwise and triple correlation of sub-pupil intensities, in order to reconstruct the image of a celestial source from its Fourier moduli and phase information, despite atmospheric turbulence. We examine the sensitivity of the method, i.e. limiting magnitude, and its implementation on existing or future high energy arrays of Cherenkov telescopes. We show that despite its poor optical quality compared to extremely large optical telescopes under construction, a Cherenkov telescope can provide diffraction limited imaging of celestial sources, in particular at the visible, down to violet wavelengths.

astro-ph.IM↗

arXiv2020

Instability threshold in a large balanced magneto-optical trap

Large clouds of cold atoms prepared in a magneto-optical trap can develop spatio-temporal instabilities when the frequency of the trapping lasers is brought close to the atomic resonance. This system bears close similarities with trapped plasmas, whereby effective Coulomb interactions are induced by the exchange of scattered photons and lead to collective nonlinear dynamics of the trapped atoms. We report in this paper a detailed experimental study of the instability threshold, and comparisons with three-dimensional simulations of the interacting, laser-driven cloud.

physics.atom-ph↗

arXiv2019

Towards a measurement of the Debye length in very large Magneto-Optical traps

We propose different experimental methods to measure the analog of the Debye length in a very large Magneto-Optical Trap, which should characterize the spatial correlations in the atomic cloud. An analytical, numerical and experimental study of the response of the atomic cloud to an external modulation potential suggests that this Debye length, if it exists, is significantly larger than what was expected.

physics.atom-ph↗

arXiv2018

Intensity Interferometry revival on the Côte d'Azur

Recent advances in photonics have revived the interest in intensity interferometry for astronomical applications. The success of amplitude interferometry in the early 1970s, which is now mature and producing spectacular astrophysical results (e.g. GRAVITY, MATISSE, CHARA, etc.), coupled with the limited sensitivity of intensity interferometry stalled any progress on this technique for the past 50 years. However, the precise control of the optical path difference in amplitude interferometry is constraining for very long baselines and at shorter wavelengths. Polarization measurements are also challenging in amplitude interferometry due to instrumental effects. The fortuitous presence of strong groups in astronomical interferometry and quantum optics at Universite Cote d'Azur led to the development of a prototype experiment at Calern Observatory, allowing the measure of the temporal correlation g(2)(τ, r=0) in 2016 and of the spatial correlation g^(2)(r) in 2017 with a gain in sensitivity (normalized in observing time and collecting area) of a factor ~100 compared to Hanbury Brown and Twiss's original Narrabri Interferometer. We present possible ways to further develop this technique and point to possible implementations on existing facilities, such as CTA, the VLTI ATs or the summit of Maunakea, which offer a unique scientific niche.

astro-ph.IM↗

arXiv2018

Magnetic Phase Diagram of Light-mediated Spin Structuring in Cold Atoms

When applying a red-detuned retro-reflected laser beam to a large cloud of cold atoms, we observe the spontaneous formation of 2D structures in the transverse plane corresponding to high contrast spatial modulations of both light field and atomic spins. By applying a weak magnetic field, we explore the rich resulting phase space and identify specific phases associated with both dipolar and quadrupolar terms of the atomic magnetic moment. In particular we demonstrate spontaneous structures in optically induced ground state coherences representing magnetic quadrupoles.

nlin.PS↗

arXiv2018

Optical long baseline intensity interferometry: prospects for stellar physics

More than sixty years after the first intensity correlation experiments by Hanbury Brown and Twiss, there is renewed interest for intensity interferometry techniques for high angular resolution studies of celestial sources. We report on a successful attempt to measure the bunching peak in the intensity correlation function for bright stellar sources with 1 meter telescopes (I2C project). We propose further improvements of our preliminary experiments of spatial interferometry between two 1 m telescopes, and discuss the possibility to export our method to existing large arrays of telescopes.

astro-ph.IM↗

arXiv2018

Synchronization of a Self-Sustained Cold Atom Oscillator

Nonlinear oscillations and synchronisation phenomena are ubiquitous in nature. We study the synchronization of self oscillating magneto-optically trapped cold atoms to a weak external driving. The oscillations arise from a dynamical instability due the competition between the screened magneto-optical trapping force and the inter-atomic repulsion due to multiple scattering of light. A weak modulation of the trapping force allows the oscillations of the cloud to synchronize to the driving. The synchronization frequency range increases with the forcing amplitude. The corresponding Arnold tongue is experimentally measured and compared to theoretical predictions. Phase-locking between the oscillator and drive is also observed.

physics.atom-ph↗

arXiv2016

Kibble-Zurek mechanism in the self-organization of a cold atomic cloud

When applying two counter-propagating laser beams to a cold cloud of Rubidium atoms, we observe the spontaneous formation of intensity patterns associated with a spatial structuration of the atomic spins. We study the average number of defects in these patterns as a function of the sweep time employed to cross the transition threshold. We observe a power-law decrease of the number of defects with increasing sweep time, typical of the Kibble-Zurek mechanism. The measured exponent is consistent with the prediction for a supercritical bifurcation.

physics.atom-ph↗

arXiv2014

Behavior of a very large magneto-optical trap

We investigate the scaling behavior of a very large magneto-optical trap (VLMOT) containing up to $1.4 \times 10^{11}$ Rb$^{87}$ atoms. By varying the diameter of the trapping beams, we are able to change the number of trapped atoms by more than 5 orders of magnitude. We then study the scaling laws of the loading and size of the VLMOT, and analyze the shape of the density profile in this regime where the Coulomb-like, light-mediated repulsive interaction between atoms is expected to play an important role.

physics.atom-ph↗

arXiv2014

Approximated center-of-mass motion for systems of interacting particles with space- and velocity-dependent friction and anharmonic potential

We study the center-of-mass motion in systems of trapped interacting particles with space- and velocity-dependent friction and anharmonic traps. Our approach, based on a dynamical ansatz assuming a fixed density profile, allows us to obtain information at once for a wide range of binary interactions and interaction strengths, at linear and nonlinear levels. Our findings are first tested on different simple models by comparison with direct numerical simulations. Then, we apply the method to characterize the motion of the center of mass of a magneto-optical trap and its dependence on the number of trapped atoms. Our predictions are compared with experiments performed on a large Rb85 magneto-optical trap.

physics.atom-ph↗

arXiv2013

Optomechanical self-structuring in cold atomic gases

The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.

physics.atom-ph↗