Symmetry breaking exhibition by magnetic field induced explicit circular dichroism

Abstract: 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 $\Delta F = \pm2$ 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 $D_2$ lines of all bosonic alkali atoms, that is transition intensity enhancement is larger for the case of $\sigma^+$ than for $\sigma^-$ excitation for $\Delta F = +2$, whereas it is larger (e.g. up to $10^{11}$ times for $^{85}$Rb atoms) in the case of $\sigma^-$ than for $\sigma^+$ polarization for $\Delta F = -2$. 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.