Researchers find superradiant intensity scales superlinearly with atom number

Researchers at Université Paris-Saclay have observed a ring-shaped emission structure corresponding to a single collective jump operator during superradiant emission from a cloud of cold rubidium atoms. Using Fourier imaging, the team detected this highly directional pattern, revealing a level of control and observation of this quantum phenomenon previously unseen. This observation confirms predictions made over two decades ago by Carmichael et al. regarding these collective jump operators, demonstrating that theoretical concepts can now be directly measured and manipulated. The work also reveals that superradiant intensity increases more than linearly with more atoms, opening possibilities for novel amplification techniques.

A single, ring-shaped emission structure observed during superradiant bursts reveals a new ability to measure and isolate collective atomic behavior. The team’s work, detailed in recent findings, utilized Fourier imaging to map the spatial pattern of light emitted from cold rubidium atoms. Experiments with up to 8000 rubidium atoms demonstrated this effect. The setup involved a glass cell and microscope objectives with a numerical aperture of 0.5, used to both trap and collect light from the atoms. The observed emission pattern differed from existing theoretical predictions; standard models assume a spin-wave forming along the cloud axis. The researchers found the emission pattern was rotationally symmetric, validating concepts introduced by Carmichael et al. [Carmichael2000]. These theoretical tools can now be measured and manipulated, opening avenues for efficient light-matter interfaces.

Recent advances in manipulating cold atomic ensembles are allowing researchers to achieve increased control over collective spontaneous emission, a phenomenon known as superradiance. Experiments utilizing clouds of up to 8000 rubidium-87 atoms are yielding insights into the fundamental mechanisms governing this process, moving beyond earlier observations limited by sample geometry. The team, based at Université Paris-Saclay, employs a sophisticated setup involving optical dipole traps and Fourier imaging to analyze the emitted radiation patterns. This experimental design allows for precise preparation of the atomic cloud, created using a magneto-optical trap and grey molasses technique, resulting in elongated structures with axial sizes ranging from 23 micrometers to 80 micrometers. The team notes systematic uncertainties of 25 percent (axial) and 20 percent (radial) in axial size determination. Analysis of the emitted light reveals a ring-shaped emission structure observed via Fourier imaging, corresponding to a single collective jump operator associated with the most superradiant mode of the ensemble. The superradiant emission exhibits superlinear scaling of the intensity with atom number.

Université Paris-Saclay researchers are exploring the boundaries of superradiance observation, moving beyond traditional, pencil-shaped atomic samples to explore collective atomic behavior with increased precision. While Dicke’s initial 1954 prediction described a burst of radiation from excited atoms, early experimental confirmations in the 1970s, like those by Skribanowitz and colleagues, relied on elongated geometries and a mean-field approach assuming a single spin-wave along the emission axis. These observations, however, didn’t fully account for the complexities arising from finite sample sizes and multiple decay channels. We observe a highly directional, ring-shaped emission structure, which corresponds to a single collective jump operator associated with the most superradiant mode of the ensemble.

The ability to sculpt and control the emission of light from atomic clouds is approaching practical application, thanks to new insights into the fundamental physics governing superradiance. Researchers at Université Paris-Saclay have moved beyond simply observing this collective glow, demonstrating a level of control previously confined to theoretical models. The team reports that collective jump operators can be measured and isolated, validating predictions that have long remained a theoretical tool. The observations align with models accounting for the complex interplay of decay channels within the atomic cloud, moving beyond simplified mean-field treatments. By isolating and analyzing these specific emission modes, the researchers are developing efficient light-matter interfaces, potentially impacting areas like quantum communication and sensing.

The expectation that superradiant emission would peak along the primary axis of an elongated atomic cloud has been challenged by recent observations at Université Paris-Saclay, revealing a rotational symmetry in the emitted light. Researchers, led by Adrien Gavalda, Guillaume Tremblier, and Martin Poitrinal, observed a ring-shaped emission structure using Fourier imaging, a pattern that doesn’t align with traditional models of superradiance predicated on the formation of a spin-wave along the cloud’s length. This result aligns with predictions made by Carmichael et al. [Carmichael2000] regarding collective jump operators, which describe how finite-size atomic ensembles undergo superradiant emission. The team was able to measure and isolate these collective jump operators associated with the most superradiant mode of the ensemble, performing experiments with up to 8000 atoms. This observation suggests a more complex interplay of collective modes than previously understood, opening new avenues for designing efficient light-matter interfaces.

A surprising ring-shaped emission structure, corresponding to a single collective jump operator associated with the most superradiant mode of the ensemble, detected from superradiant atomic clouds challenges conventional understanding of collective atomic behavior. This level of control over the emission process, detailed in recent findings, allows for precise examination of the underlying quantum mechanics. The observed pattern exhibits rotational symmetry, and the experimental design enabled isolation of this specific emission channel. By employing spatial filtering, the researchers confirmed superlinear scaling of the intensity with atom number, demonstrating that the intensity does not simply increase proportionally with more atoms. The team’s results bridge a significant gap between theoretical prediction and experimental observation, and the ability to manipulate these jump operators opens avenues for designing novel light-matter interfaces with enhanced efficiency.

Following observations of a distinct ring-shaped emission structure using Fourier imaging, researchers at Université Paris-Saclay have quantified the superlinear scaling of the intensity with atom number. They confirmed this relationship by isolating the superradiant channel through spatial filtering, performing experiments with up to 8000 atoms. The calculated Gaussian rms axial sizes vary from 23 to 80 micrometers, with systematic uncertainties of 25 percent (axial) and 20 percent (radial). The team found the intensity of superradiant bursts scales superlinearly with the number of atoms involved.

The apparatus utilizes three microscope objectives, each with a numerical aperture of 0.5, serving a dual purpose: to both trap and collect light emitted from clouds of rubidium-87 atoms. These clouds, created from a magneto-optical trap and refined using grey molasses, are held within an optical dipole trap, a focused laser beam with a tunable waist ranging from 2.5 to 8 micrometers. The system is capable of generating elongated atomic clouds containing up to 8000 atoms, maintained at temperatures between 550 and 1550 microKelvin. Precise control over cloud geometry is achieved, with calculated Gaussian rms axial sizes varying from 23 to 80 micrometers. A crucial element is the application of a 64 Gauss magnetic field perpendicular to the cloud axis, isolating a specific transition for resonant excitation with a linearly polarized laser beam. This excitation yields an initial excited state population of 88 percent. Following excitation and subsequent decay, the emitted light is captured and analyzed using Fourier imaging. “We image the emitted light in Fourier space by conjugating the back focal plane of the objective with an EMCCD camera,” explain the researchers, allowing for detailed mapping of the spatial emission pattern.