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arXiv:2403.17707 · Optics Letters

Effect of light-assisted tunable interaction on the position response function of cold atoms

Anirban Misra, Urbashi Satpathi, Supurna Sinha, Sanjukta Roy, Saptarishi Chaudhuri

Published Jul 9, 2024• 2 citations
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Abstract

The position response of a particle subjected to a perturbation is of general interest in physics. We study the modification of the position response function of an ensemble of cold atoms in a magneto-optical trap (MOT) in the presence of tunable light-assisted interactions. We subject the cold atoms to an intense laser light tuned near the photoassociation (PA) resonance and observe the position response of the atoms subjected to a sudden displacement. Surprisingly, we observe that the entire cold atomic cloud undergoes collective oscillations. We use a generalized quantum Langevin approach to theoretically analyze the results of the experiments and find good agreement.

DOI
10.1364/ol.532095

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The position response of a particle subjected to a perturbation is of general interest in physics. We study the modification of the position response function of an ensemble of cold atoms in a magneto-optical trap (MOT) in the presence of tunable light-assisted interactions. We subject the cold atoms to an intense laser light tuned near the photoassociation (PA) resonance and observe the position response of the atoms subjected to a sudden displacement. Surprisingly, we observe that the entire cold atomic cloud undergoes collective oscillations. We use a generalized quantum Langevin approach to theoretically analyze the results of the experiments and find good agreement.
In the context of non-equilibrium statistical physics, the position response of a particle, coupled to a bath, subjected to an external force is a topic of broad interest. A topic of further interest is two distinguishable sets of interacting particles in contact with two distinct baths. Here, we report the experimental evidence of the modification of the position response function (PRF) of an ensemble of cold atoms in a magneto-optical trap when it is placed alongside a dilute cloud of cold atoms of a different species. Our experiment consists of a mass-imbalanced cold atomic mixture of 39 K and 23 Na atoms. We focus on the position response of 39 K atoms when subjected to a sudden displacement in the presence of a cold 23 Na atomic cloud. Notably, we find that, in the underdamped regime of motion, the oscillation frequency of motion of the cold atoms changes as much as 30 % depending on the effective inter-species light-assisted interaction strength. On the other hand, in the overdamped regime, there is a reduction, as high as 10.5 %, in the damping coefficient, depending on the interaction strength. Using a generalized quantum Langevin approach, we develop a theoretical framework, compare it with the experimental results, and find good agreement. Our results are expected to find applications in the domain of mass and charge transport studies in a wide variety of physical conditions, which can be simulated in cold atom experiments.
We report our experimental measurements and theoretical analysis of the position response function of cold atoms in a magneto-optical trap (MOT) by applying a transient homogeneous magnetic field as a perturbing force. We observe a transition from a damped oscillatory motion to an over-damped relaxation, stemming from a competition between the viscous drag provided by the optical molasses and the restoring force of the MOT. Our observations are in agreement with the predictions of our model based on the Langevin equation. We also study the diffusion of the atomic cloud in the optical molasses and find the measured value of diffusion coefficient matching with the prediction of our theoretical model.
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Light propagation in disordered media is a fundamental and important problem in optics and photonics. In particular, engineering light-matter interaction in disordered cold atomic ensembles is one of the central topics in modern quantum and atomic optics. The collective response of dense atomic gases under light excitation, which crucially depends on the spatial distribution of atoms and the geometry of the ensemble, has important impacts on quantum technologies like quantum sensors, atomic clocks and quantum information storage. Here we analyze near-resonant light transmission in two-dimensional dense ultracold atomic ensembles with short-range positional correlations. Based on the coupled-dipole simulations under different atom number densities and correlation lengths, we show that the collective effects are strongly influenced by those positional correlations, manifested as significant shifts and broadening or narrowing of transmission resonance lines. We also analyze the eigenstate distribution of different atomic ensembles. This work may provide profound implications on collective and cooperative effects in cold atomic ensembles as well as the study of mesoscopic physics concerning light transport in strongly scattering disorder media.
Light–matter interaction in cold atomic ensembles is one of the central topics in modern quantum and atomic optics with important applications in various quantum technologies. The collective response of dense atomic gases under light excitation depends crucially on the spatial distribution of atoms and the geometry of the ensemble. We analyze near-resonant light transmission in two-dimensional dense ultracold atomic ensembles with short-range positional correlations. Based on coupled-dipole simulations, we show that the collective effects, manifested as notable shifts of transmission resonance frequency and considerable modification of optical depths, are influenced strongly by positional correlations. Mean-field theories such as the Lorentz–Lorenz relation are not capable of describing such collective effects. We also investigate the statistical distribution of eigenstates and provide a connection between the transmission spectra and eigenstate distribution by utilizing the population weighted detuning and decay rate of all eigenstates. We further demonstrate the intricate interplay between dipole–dipole interactions and positional correlations by increasing the number densities of atoms.