Ultraslow propagation of squeezed vacuum pulses with electromagnetically induced transparency

We have succeeded in observing ultraslow propagation of squeezed vacuum pulses with electromagnetically induced transparency. Squeezed vacuum pulses (probe lights) were incident on a laser-cooled Rb-87 gas together with an intense coherent light (control light). A homodyne method sensitive to the vacuum state was employed for detecting the probe pulse passing through the gas. A delay of 3.1 mu s was observed for the probe pulse having a temporal width of 10 mu s.