Laser-Driven Superradiant Ensembles of Two-Level Atoms near Dicke Regime

G. Ferioli, A. Glicenstein, F. Robicheaux, R. T. Sutherland, A. Browaeys, and I. Ferrier-Barbut

Phys. Rev. Lett. 127, 243602 – Published 10 December 2021

Abstract

We report the experimental observation of a superradiant emission emanating from an elongated dense ensemble of laser cooled two-level atoms, with a radial extent smaller than the transition wavelength. In the presence of a strong driving laser, we observe that the system is superradiant along its symmmetry axis. This occurs even though the driving laser is orthogonal to the superradiance direction. This superradiance modifies the spontaneous emission, and, resultantly, the Rabi oscillations. We also investigate Dicke superradiance in the emission of an almost fully inverted system as a function of the atom number. The experimental results are in qualitative agreement with ab-initio, beyond-mean-field calculations.

Received 28 July 2021
Accepted 3 November 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.243602

Physics Subject Headings (PhySH)

Light-matter interaction Quantum optics Spontaneous emission

Atomic gases

Cooling & trapping Light scattering

Atomic, Molecular & Optical

Authors & Affiliations

G. Ferioli^1,*, A. Glicenstein¹, F. Robicheaux ^2,3,†, R. T. Sutherland ^4,‡, A. Browaeys¹, and I. Ferrier-Barbut¹

¹Université Paris-Saclay, Institut d’Optique Graduate School, CNRS, Laboratoire Charles Fabry, 91127, Palaiseau, France
²Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
³Purdue Quantum Science and Engineering Institute, Purdue University, West Lafayette, Indiana 47907, USA
⁴Department of Electrical and Computer Engineering, Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249, USA

^*giovanni.ferioli@institutoptique.fr
^†robichf@purdue.edu
^‡robert.sutherland@utsa.edu

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Vol. 127, Iss. 24 — 10 December 2021

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Images

Figure 1
Experimental setup and observation of collective Rabi oscillations. (a) Sketch of the experimental setup. The excitation beam is aligned along the magnetic field $B$ and propagates along $\hat{z} - \hat{y}$ . (b) Photon rate along the axis of the cloud versus time. For low $N$ (blue solid line) the dynamics is reproduced by the solution of the OBEs for a single atom (black dashed). For large $N = 2780$ (red solid), the experimental results agree qualitatively with MF2 calculations (gray dot-dashed). (c) Photon rates measured in the radial direction for $N = 2780$ . In this direction, the dynamics remains consistent with the single-atom OBEs for all $N$ .
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Figure 2
Observation of collective Rabi oscillations. (a) Filled (empty) diamonds: measured ratios of the peak to steady-state emission rates for the collective Rabi oscillations recorded along the axial (radial) direction of the cloud. Gray points: results of the numerical simulations performed with the MF2 model (see text). The vertical error bars represent the standard error in the estimation of the steady state (smaller than symbols). Black dashed line: results from the OBEs. Inset: total photon emission rate (in a $4 π$ solid angle) per atom $Γ (t) / N$ , calculated with MF2, for small and large $N$ . (b) Diamonds: measured Rabi frequencies. The error bars represent the variance of the Gaussian distribution used to fit the experimental spectra. Gray area: expected value for the single atom Rabi frequency $Ω / Γ_{0} = \sqrt{s / 2}$ , including the experimental error on the intensity of the excitation beam. Inset: delay of the position of the maximum at the first Rabi fringe versus atom number (gray line, MF2 simulations). Error bars show the finite time resolution of the detector (1 ns).
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Figure 3
Observation of superradiant emission for an inverted system. Examples of experimental photon rates recorded along the axial direction of the cloud, normalized by the value of $N$ for the cloud. The definition of the characteristic superradiant time (see text) is schematically shown on the $N = 4700$ trace. The black vertical line represents the end of the excitation pulse, represented by the gray shaded area.
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Figure 4
Analysis of the superradiant decay. (a) Peak photon emission of the superradiant burst normalized by $N$ as a function of $N$ . The error bars are the quadratic sum of the standard error on the peak position and on $N$ . (b) and (c) $1 / e$ -decay time and initial slope of the superradiant emission rate at $t = 0$ . In (b) the error bars represent the temporal resolution of the detector while in (c) they are evaluated from the errors in the linear fit. Gray circles: results of the numerical simulations using the MF2 model.
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