Eur. Phys. J. D (2013) 67: 213
https://doi.org/10.1140/epjd/e2013-40285-0

Regular Article

Observation of spontaneous quantum fluctuations in photon absorption by atoms

Research and Education Center for Natural Sciences and Hiyoshi Dept. of Physics, Keio University, 223–8521 Yokohama, Japan

^a e-mail: ken@phys-h.keio.ac.jp

Received: 21 March 2013
Received in final form: 8 July 2013
Published online: 18 October 2013

Abstract

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, 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, whose whole structure 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.