  Using a nondegenerate four-wave mixing (FWM) process based on a
double-{\Lambda} scheme in hot cesium vapor, we demonstrate a compact
diode-laser-pumped quantum light source for the generation of quantum
correlated twin beams with a maximum squeezing of 6.5 dB. The squeezing is
observed at a Fourier frequency in the audio band down to 0.7 kHz which, to the
best of our knowledge, is the first observation of sub-kilohertz
intensity-difference squeezing in an atomic system so far. A phase-matching
condition is also investigated in our system, which confirms the
spatial-multi-mode characteristics of the FWM process. Our compact
low-frequency squeezed light source may find applications in quantum imaging,
quantum metrology, and the transfer of optical squeezing onto a matter wave.
