We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.
The amplitude of Λ resonance in alkali atoms is limited by perturbing cycling transitions in the case of D2 line or by existence of additional trapping states in the case of D1 line. We propose to eliminate these extra trapping states by using two counter-propagating bichromatic fields of orthogonal circular polarizations. The experiment is in accordance with the theoretical proposal. The result refers to small-size cells and is important for applications in miniaturized atomic clocks. The dependence of the CPT signal amplitude on the position of the mirror with respect to the vapor cell
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