Magnetic field-induced symmetry breaking exhibited by explicit circular dichroism for
ΔF=±2 transitions of D
2 lines of all alkali atoms
In this letter we demonstrate universal symmetry breaking by means of magnetically induced circular dichroism. Magnetic field induces forbidden at zero field atomic transitions between
ΔF=±2 hyperfine levels. In a particular range of magnetic field, intensities of these transitions experience significant enhancement. We have deduced a general rule applicable for the
D2 lines of all bosonic alkali atoms, that is transition intensity enhancement is larger for the case of
σ+ than for
σ− excitation for
ΔF=+2, whereas it is larger (e.g. up to
1011 times for
85Rb atoms) in the case of
σ− than for
σ+ polarization for
ΔF=−2. This asymmetric behaviour results in an explicit circular dichroism. For experimental verification we employed half-wavelength-thick atomic vapor nanocells using a derivative of selective reflection technique, which provides sub-Doppler spectroscopic linewidth ($\sim$50 MHz). The presented theoretical curves well describe the experimental results. This effect can find applications particularly in parity violation experiments.
The influence of negative-energy states (NES) on forbidden magnetic-dipole ${\mathrm{ns}}_{1/2}\ensuremath{-}(n+1){s}_{1/2}$ transitions in alkali-metal atoms is investigated. We find that the NES contributions are significant in almost all cases and, for rubidium, reduce the transition rate by a factor of 8. We tabulate magnetic-dipole
(M1) transition amplitudes for the alkalis. Our
M1 value for cesium, where accurate measurements are available, differs from experiment by
16. We briefly discuss the feasibility of an experimental test of NES effects.
Abstract Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to | F g = F , m F = 0 ⟩ → | F e = F , m F = 0 ⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D 2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.