  Storage and retrieval of parametric down-conversion (PDC) photons are
demonstrated with electromagnetically induced transparency (EIT). Extreme
frequency filtering is performed for THz order of broadband PDC light and the
frequency bandwidth of the light is reduced to MHz order. Storage and retrieval
procedures are carried out for the frequency filtered PDC photons. Since the
filtered bandwidth [full width at half-maximum (FWHM) = 9 MHz] is within the
EIT window (FWHM = 12.6 MHz), the flux of the PDC light is successfully stored
and retrieved. The nonclassicality of the retrieved light is confirmed by using
photon counting method, where the classical inequality which is only satisfied
for classical light fields is introduced. Since the PDC photons can be utilized
for producing the single photon state conditionally, storage and retrieval
procedures are also performed for the conditional single photons.
Anti-correlation parameter used for checking the property of single photon
state shows the value less than 1, which means the retrieved light is in a
non-classical region.
