Electric-dipole forbidden transitions for probing atomic state preparation: the case of the Autler–Townes effect

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This work demonstrates an scheme in which a weak electric quadrupole ( E 2) transition with a controlled frequency detuning in a ladder configuration is used as an extremely non-perturbing probe for precisely identifying subtle details of the effects driven by AC fields coupling atomic states and the preparation of quantum states. For this purpose, we provide a precise experimental and theoretical study of the Autler Townes (AT) effect derived from a strong electric dipole transition stimulated by a resonant laser beam and probed by the E 2 interaction. The experiment was carried out for a 87 Rb atomic gas at room temperature in a velocity-selective scheme. The AT effect was monitored via the splitting of the fluorescence spectra associated with the spontaneous decay to the ground state. The theoretical description incorporates the modification of standard few-level schemes introduced by forbidden electric-dipole transitions selection rules. We develop an analytic ladder three-level scheme to approximate the cyclic 5S 1/2 F = 2 → 5P 3/2 F = 3 → 6P 3/2 F = 1, 2, 3 → 5S 1/2 F = 2 path. Other levels that could have effects on the fluorescence are included via a fourth level with effective parameters. Doppler effects and finite bandwidths of the laser beams are included in the theoretical model to closely reproduce the experimental results.