  Fluctuations in light absorption by atoms are observed by applying laser
light on rubidium atoms and measuring the transmitted light intensity
fluctuations. These fluctuations are spontaneous noise, which are generic to
photon atom interactions. By making use of the sub-shot noise random signal
detection technology, we have measured the spectra at sub-shot noise levels to
reveal their rich nature, which had previously been unobserved. The effects of
atoms transiting the laser beam, Rabi flopping in the optical transitions and
Larmor precession of the magnetic moment are observed in the spectra. The
properties of the fluctuations reflect not only the quantum behavior of atoms,
but also that of light.
