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Physical Review A

Significant enhancement of group delay in electromagnetically induced transparency with a spatially partially coherent coupling field

You-Lin Chuang

Published Dec 13, 2023• 0 citations
Publisher

Abstract

The slow light propagation effect in electromagnetically induced transparency with a spatial partially coherent coupling field has been studied. We find that the group velocity of the probe beam can be significantly reduced when the spatial coherence of the coupling field decreases. It shows that the group delay of the probe beam can achieve about 10 times that of the fully coherent case. This work shows the effect of spatial coherence of the coupling field in a coherent atomic medium and provides a slow-light mechanism in optical coherence systems.

DOI
10.1103/physreva.108.063707

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The slow light propagation effect in electromagnetically induced transparency with a spatial partially coherent coupling field has been studied. We find that the group velocity of the probe beam can be significantly reduced when the spatial coherence of the coupling field decreases. It shows that the group delay of the probe beam can achieve about 10 times that of the fully coherent case. This work shows the effect of spatial coherence of the coupling field in a coherent atomic medium and provides a slow-light mechanism in optical coherence systems.
We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.
When a coherently prepared atomic medium is confined in an optical cavity, the atomic coherence and interference manifested by electromagnetically induced transparency (EIT) can be manipulated and enhanced by the collective atom–cavity coupling and the cavity feedback. We present an experimental study of the light transmission through an optical cavity coupled with coherently prepared cold Rb atoms. In the frequency domain, the cavity transmission spectrum exhibits spectral peaks representing the cavity normal modes associated with the multi-atom vacuum Rabi splitting and the intra-cavity dark state manifested by the combined EIT effects of the absorption suppression and the steep normal dispersion. In the time domain, a light pulse coupled into the cavity mode propagates with a slow group velocity and the propagation time delay is significantly increased by the cavity feedback.
Summary form only given. Electromagnetically induced transparency (EIT) has been the subject of many experimental and theoretical studies over recent years. Most recently, substantial experimental and theoretical work in this area has been focused on the use of EIT to give ultraslow group velocities for light in both ultracold atomic gas and hot atomic vapors. Much of this interest is based on the fact that slowing the group velocity of a laser pulse down to the speed of sound in the same material can produce strong coupling between acoustic waves and the electromagnetic field. It has been suggested that a giant nonlinearity obtained by this method might be utilized for efficient multi-wave mixing and quantum nondemolition measurements. Slow light might also allow a very efficient nonlinear interaction between laser pulses of extremely low (down to a single photon) energies. Here, we report the first direct observation of an ultraslow group velocity of light down to 45 m/s in a solid, well below the speed of sound in the medium. This group velocity is fundamentally limited only by the inhomogeneous broadening of the ground state transition. At low coupling beam intensities, the fraction of centers that are pumped into the "dark state" increases with coupling laser power, so that the observed group delay is increasing with coupling beam intensity. At higher intensities, power broadening reduces the sharpness of the dispersive feature and the observed group delay decreases.
Electromagnetically-induced transparency (EIT) in three-level Λ-systems is based on quantum interference effects involving coherence between the two lower levels, which allow propagation of a resonant probe light beam in the presence of a strong coupling field. We have observed transparency in ultra-narrow (<10 kHz) windows at the resonant 1.083 μm transition for purely electronic spins in gaseous 4 He* at room temperature. Slow light is an interesting outcome of the EIT phenomenon due to extreme dispersion within the narrow transparency window. We have obtained group delays of about 4 μs in a 2.5 cm long He* cell. A complete theoretical analysis explains our observations emphasizing the positive role of collisions. Slow light with 1-GHz Doppler broadening opens the door to applications of controllable large-bandwidth delays in radars.
We describe the temporal and spatial dynamics of propagating electromagnetically induced transparency pulses in an optically thick medium. Results include pulse velocities as slow as c/165c/165c/165 with 55% transmission, strong-probe-field effects, and the observation of near diffraction-limited transmitted beam quality.
We propose a configuration that utilizes electromagnetically induced transparency (EIT) to tailor a fiber mode propagating inside a thin optical fiber and coherently control its dispersion properties to drastically reduce the group velocity of the fiber mode. The key to this proposal is that the evanescent field of the thin fiber strongly couples with the surrounding active medium, so that the EIT condition is met by the medium. We show how the properties of the fiber mode are modified due to the EIT medium, both numerically and analytically. We demonstrate that the group velocity of the modified fiber mode can be drastically reduced $(\ensuremath{\approx}44\mathrm{}\mathrm{m}/\mathrm{s}\mathrm{e}\mathrm{c})$ using the coherently prepared orthohydrogen doped in a matrix of parahydrogen crystal as the EIT medium.