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Physical Review A

Optical beating spectroscopy of polarizabilities produced by two-photon absorption

M. D. Levenson

Published Jun 1, 1976• 7 citations
Publisher

Abstract

Two-photon absorption can produce a coherent oscillating atomic polarizability in a macroscopic vapor. If this vapor contains an ensemble of atoms having different transition frequencies, the beat frequencies between the polarizabilities of the two species can be detected in the time domain. Energy-level splittings can be determined which are too small to resolve in the frequency domain and are not accessible to quantum beats.

DOI
10.1103/physreva.13.2314

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Two-photon absorption can produce a coherent oscillating atomic polarizability in a macroscopic vapor. If this vapor contains an ensemble of atoms having different transition frequencies, the beat frequencies between the polarizabilities of the two species can be detected in the time domain. Energy-level splittings can be determined which are too small to resolve in the frequency domain and are not accessible to quantum beats.
We extend the technique of quantum-beat spectroscopy to the infrared region by utilizing the strong, directional absorption and emission which occurs in photon echoes and optical nutation. Using a vibrational transition of NH2{\mathrm{H}}_{2}H2​D, we have made the first observations of infrared quantum beats in these phenomena. The hyperfine splitting which produces the quantum beats has not been observed in Lamb-dip spectroscopy but is clearly resolved in these time domain studies.
Quantum beats, the fact that periodic oscillations arise from coherent superposition of frequency-distinguishable states, have enabled various quantum information technologies beyond the possibilities of classical physics. Although the conventional quantum beats are based on unitary optical elements, we present that nonunitary material provides an alternative degree-of-freedom to control the quantum interference and even enables the observation of anomalous quantum beating signals. An elaborate lossy film is used to explore its tunability over the effective photon–photon interaction in frequency modes, which may introduce sophisticated nonunitary realization into integrated optical platforms. In addition, we confirm its ability of harnessing the suppression and enhancement of single- and two-photon absorption by manipulating the symmetric property of frequency entanglement, and this would provide significant benefits in entanglement-assisted absorption spectroscopy. These results show an alternative method to investigate the quantum light–matter interaction, facilitating the use of two-photon interference for quantum light-based spectroscopy and microscopy.
We present results on photon echo spectroscopy for resonant excitation of localized charged exciton complexes (trions) in CdTe/CdMgTe semiconductor quantum wells. We demonstrate that the Zeeman splitting of resident electron spin levels in transverse magnetic field leads to quantum beats in the photon echoes with the Larmor precession frequency. This allows us to perform a coherent transfer of optical excitation into a spin ensemble and to observe long-lived photon echoes. Our approach can be used as a tool for remarkably high resolution spectroscopy of the ground state levels: We are able to resolve splittings between the spin levels with sub-µeV precision and to distinguish between different types of electrons in the ensemble, namely electrons either bound to donors or localized on quantum well potential fluctuations. To that end we show that stimulated step-like Raman processes in the two-pulse excitation scheme allow us to probe the electron spin ensemble with high selectivity and precision even for systems with broad optical transitions. Next, Rabi oscillations for exciton complexes with different degree of localization are detected by photon echo spectroscopy. We observe that an increase of the area of either the first or the second pulse leads to a significant decrease of the photon echo signal, which is strongest for the neutral excitons and less pronounced for the donor-bound exciton complex.