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Physicae Proceedings

Noise spectroscopy in cold Rubidium atoms in EIT configuration

Klara Theophilo

Published Mar 29, 2012• 0 citations
Publisher

Abstract

Using noise spectroscopy, we studied the correlations between two light beams with opposite circular polarization, coupling the transition F=2 -> F’=2 in Λ EIT configuration, with cold atoms of Rubidium-85. In the spectrum of correlation we observed the transition from correlation to anti-correlation, off-resonance, when raising the potency of the beams.This transition is a consequence of the competition between four-wave mixing, which is responsible for the correlation regime, and the Stark effect that produces anti-correlation in the beams.In the spectra of mean signal of intensity and correlation, we observed that the EIT peak is free of potency broadening, which makes possible that the measure of coherence time be more precise in the condition of EIT. Using a EIT’s model for a system in Λ configuration, we observed that the theoretical correlation spectra are in good accordance with the experimental data, considering the degenerescence of the hyperfine levels. Besides that, the model predicts the non-broadening of the correlation peak, showing the correlation as a characterization property more accurated than the mean signal of intensity.

DOI
10.5196/physicae.proceedings.xiyrm.33

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Using noise spectroscopy, we studied the correlations between two light beams with opposite circular polarization, coupling the transition F=2 -> F’=2 in Λ EIT configuration, with cold atoms of Rubidium-85. In the spectrum of correlation we observed the transition from correlation to anti-correlation, off-resonance, when raising the potency of the beams.This transition is a consequence of the competition between four-wave mixing, which is responsible for the correlation regime, and the Stark effect that produces anti-correlation in the beams.In the spectra of mean signal of intensity and correlation, we observed that the EIT peak is free of potency broadening, which makes possible that the measure of coherence time be more precise in the condition of EIT. Using a EIT’s model for a system in Λ configuration, we observed that the theoretical correlation spectra are in good accordance with the experimental data, considering the degenerescence of the hyperfine levels. Besides that, the model predicts the non-broadening of the correlation peak, showing the correlation as a characterization property more accurated than the mean signal of intensity.
We report a detailed investigation on the properties of intensity correlation spectra for laser beams interacting with cold atoms under the condition of electromagnetically induced transparency (EIT). We describe the transition of their intensity fluctuations from correlation to anticorrelation as the mean intensity of the fields increases. Such a transition occurs for laser frequencies around the EIT resonance, which is characterized by a correlation peak. The transition point between correlation and anticorrelation is independent of power broadening and provides directly the ground-state coherence time. We introduce a method to extract in real time the correlation spectra of the system. The experiments were done in two distinct magneto-optical traps, one for cesium and the other for rubidium atoms, employing different detection schemes. A simplified theory is introduced assuming three-level atoms in $\ensuremath{\Lambda}$ configuration interacting with a laser with stochastic phase fluctuations, providing a good agreement with the experimental observations.
Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is also shown.
The electromagnetic induced transparency (EIT) has attracted a lot of attention since its aplications in quantum information were discovered.However, transient dynamics in this context were not as well explored.Here, we present a study of a cold rubidium ensemble under electromagnetic induced transparency (EIT), during a transient interaction.Using noise correlation spectroscopy, which is a more sensitive technique than a mean intensity spectroscopy, we investigated an asymmetric atomic response to an increasing or decreasing frequency scanning of the probe beams in the Λ-EIT system.The observation of this asymmetry, which could not be explained by the theoretical predictions based on the Bloch equations for 3-level atom, the previously used model, launched us in a search for possible causes of this enigmatic eect.Straightforward, several hypotheses were formulated, resulting in a wide experimental exploration, including parameters as the angle between the EIT beams, detuning, power and direction of incidence of the repump beam.In addition, spectra in the time domain were studied in order to understand the evolution of the system to the steady-state.Parallel to the experiment, we developed new theoretical models.Our latest theoretical approach models the system as an atom of 5-levels in which 3 levels are related to the Λ system and the other two levels are coupled by the repump.Moreover, we also consider the optical forces in the system.This model has obtained good agreement with the experimental data, for mean intensity spectroscopy.
Correlation spectroscopy has been proposed as a spectroscopic technique for measuring the coherence between the ground states in electromagnetically induced transparency (EIT). While in the time domain the steep dispersion in the EIT condition accounts for the robustness of the correlation linewidth against power broadening, such physical insight was not directly established in the frequency domain. We propose a perturbative approach to describe the correlation spectroscopy of two noisy lasers coupled to a $\mathrm{\ensuremath{\Lambda}}$ transition in cold atoms, leading to EIT. Such approach leads to an analytical expression that maps the intensity correlation directly in terms of the absorption and dispersion of the light fields. Low and high perturbative regimes are investigated and demonstrate that, for coherent light sources, the first-order term in perturbation expansion represents a sufficient description for the correlation. Sideband resonances are also observed, showing the richness of the frequency domain approach.
Enhanced sensitivity in electromagnetically induced transparency (EIT) can be obtained by the use of noise correlation spectroscopy between the fields involved in the process. Here, we investigate EIT in a cold (<1<1<1 mK) rubidium vapor and demonstrate sensitivity to detect weak light-induced forces on the atoms. A theoretical model is developed and shows good agreement with our measurements, enabling the attribution of the observed effects to the coupling of the atomic states to their motion. The effects remain unnoticed on the measurement of the mean fields but are clearly manifest in their correlations.
Abstract Polarization rotation in electromagnetically induced transparency (PREIT) in rubidium vapour at room temperature has been studied experimentally as well as theoretically in the absence of any magnetic field. PREIT is observed for both 85 Rb and 87 Rb combining the D 1 and the D 2 transitions with a V-type configuration. For 85 Rb, two EIT peaks and for 87 Rb, one EIT peak were observed. Nonlinear characteristics of the variations of the angle of rotation corresponding to the EIT position were observed for both the isotopes of Rb. We have modelled a four level system to explain the occurrence of the double EIT in case of the 85 Rb and the occurrence of one EIT peak for 87 Rb. The rotation of plane of polarization of the probe beam can be further explained with this model. The characteristic behaviour of the variation of rotation corresponding to the EIT position from theoretical analysis has matched well with the experimental observations. A sharp rotation with a high signal to noise ratio in the vicinity of the EIT can be used as a modulation free and noise insensitive signal for the frequency stabilization.