Feasibility of using Bose-Einstein condensates for filtering optical pulses

Abstract

The feasibility of using the extreme slowing down of light in Bose-Einstein condensates of alkali metal atoms as a means of improving the spectral characteristics of optical signals is studied. The basis of this approach is the resonant character of the slowing down of electromagnetic pulses in these media. In other words, signals with frequency characteristics close to the intervals between levels in the energy spectrum of alkali metal atoms in a Bose-Einstein condensate are slowed down the most. The filtering of electromagnetic signals is described in terms of a microscopic theory for the response of a gas of hydrogenlike atoms to a weak external electromagnetic field. The possibility in principle of signal filtering is demonstrated using the example of an electromagnetic pulse with a normal (gaussian) spectral intensity distribution propagating through a rarefied gas of alkali metal atoms in a Bose-Einstein condensate state. We study in detail the use of the shift in the hyperfine Zeeman levels of sodium atoms in a homogeneous, external, constant magnetic field with an appropriate choice of the Zeeman sublevel populations of the ground states of these atoms. Conditions are determined such that, when an optical signal propagates through a condensate, it is possible to isolate components of that signal with strictly defined frequencies from residual low intensity noise. It is also shown that if the resulting filtered signal is repeatedly passed through a condensate with a different value of the magnetic field, noise can essentially be eliminated entirely from the optical signal.