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Journal of Physics B Atomic Molecular and Optical Physics

Squeezing-induced resonant finite refractive index - zero absorption

Saad S. M. Hassan, Hanan Ali Batarfi, Siew-Yoong Ng, Mohamed Ridza Wahiddin

Published Nov 14, 1997• 5 citations
Publisher

Abstract

We demonstrate that the spectra of a probe beam probing an ensemble of two-level atoms damped by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by zero absorption when the probe beam frequency is tuned to the laser frequency. This resonant effect is due to coherent population oscillations. The same theoretical model also exhibits a large refractive index with zero absorption at the Rabi sidebands and near resonance. These results may be verified by present experiments.

DOI
10.1088/0953-4075/30/21/009

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We demonstrate that the spectra of a probe beam probing an ensemble of two-level atoms damped by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by zero absorption when the probe beam frequency is tuned to the laser frequency. This resonant effect is due to coherent population oscillations. The same theoretical model also exhibits a large refractive index with zero absorption at the Rabi sidebands and near resonance. These results may be verified by present experiments.
we demonstrate that spectra of a probe beam probing an ensemble of tow -level atoms damped by a broadband squeezed vacuum and driven by weak laser may exhibit a large refractive index by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by resonant effect is due to coherent population oscillations . the same theoretical model also exhibits a large refractive index with zero absorption at the rabi sidebands and near resonance . these results may be verified by present experiments
A comprehensive study is made of the absorption spectrum of a weak-probe beam irradiating a two-level atom damped by a broadband squeezed vacuum and driven by a strong laser field. We show that for a resonant driving field whose phase does not coincide with the principal directions of the squeezing ellipse, the absorption spectrum is asymmetric and exhibits absorption-emission profiles at the Rabi sidebands. We find that this feature arises from unequal populations of the dressed states of the system, which occur when all components of the Bloch vector are coupled to the driving field. A symmetric spectrum with dispersionlike profiles at the Rabi sidebands is revealed for an off-resonant driving field. Furthermore, the spectrum may exhibit an emission profile at the central frequency, signifying an amplification of the probe beam. We point out that the amplification at the central component is not attributed to population inversion in both the atomic bare states and in the dressed atomic states. We find that the amplification originates from the coherent population oscillations and is impossible in the absence of the squeezed vacuum. In addition, we examine how these features are affected by the detuning of the driving field and an imperfect squeezed vacuum.
We study the absorption spectra of a weak probe beam that interacts with a driven two-level atom in the presence of a squeezed vacuum. In particular, we focus on the behavior of the central resonance of the probe absorption spectra in the region of intermediate driving intensities and in the large squeezed photon number limit. Squeezing-induced pimples, hole-burning, and dispersive profiles at line center are displayed. These unusual spectral features are highly sensitive to the squeezing phase and to the Rabi frequency of the driving field. We present analytical conditions for the occurrence of these effects and find that they all take place in the vicinity of the critical point dividing the different dynamical regimes, probe absorption and amplification, of the atomic radiation. We also investigate analytically and numerically the two-time correlation functions of the atomic polarization and find that the cross correlations of the two dipole quadratures contribute symmetric (absorptionlike) spectral features to the absorption spectra, whereas the self-correlations contribute asymmetric (dispersionlike) spectral profiles, which disappear for the particular phase values Φ = 0, π. The physical origin of the unusual spectral profiles at line center is also discussed in terms of the coherent population oscillations.
The authors present analytical and numerical results for resonance fluorescence produced by a two-level atom damped by a broad-band squeezed vacuum. Previous theoretical analyses of this model have assumed that the laser frequency and the carrier frequency of the squeezed vacuum are equal. The authors introduce a non-zero detuning between the laser frequency and the carrier frequency while maintaining resonance between the laser frequency and atomic resonance. In the absence of the driving field there is a squeezing threshold: above threshold the decay rate of the atomic polarization can be reduced, and below threshold a squeezing-induced two peak spectrum and frequency shift, which is analogous to the Bloch-Siegert shift, are predicted. In the presence of the driving field, the spectrum is asymmetric for Rabi frequencies smaller or comparable to the detuning of the squeezed vacuum. A symmetric spectrum is obtained for large Rabi frequencies. An interpretation is predicted by means of a dressed-state analysis. The authors find that for not too large Rabi frequencies a remarkably large population inversion can be induced in the dressed states, even at exact resonance of the driving field, provided that the laser frequency and carrier frequency are detuned. Moreover, for detection times larger than the inverse detuning, the spectrum is insensitive to the phase between the driving field and the squeezed vacuum, in marked contrast to the case of no detuning.
Abstract A study of the absorption spectrum of a weak-probe beam irradiating a two-level quantum emitter with broken inversion symmetry driven by external monochromatic high-frequency electromagnetic (e.g. laser) field and damped by squeezed vacuum reservoir with finite bandwidth was carried out for the case of the squeezed vacuum source being represented by a non-degenerate parametric oscillator below threshold. It was shown that this atom-driving-field system can either amplify or absorb weak probe electromagnetic radiation beam of much lower frequency than the frequency of the driving field. The shape of the absorption and amplification spectra can be controlled by the degree of the squeezed vacuum source degeneration and by the phase of the squeezing, while the switching between these two modes of operation can only be controlled by the phase of the squeezing.