Generation of squeezed states and twin beams via non-degenerate four-wave mixing in a Λ system

We show that non-degenerate four-wave mixing in a Λ system yields strong suppression of quantum phase noise when the probe and conjugate beams are monitored via balanced homodyne detection. Unlike previous calculations performed on similar system, we include situations where the pump beams become resonant with the corresponding two-level transitions. As a result, we find conditions wherein strong squeezing can be achieved with relatively low pump powers. Furthermore, we show explicitly, via numerical integration, that the probe and the conjugate beams, each starting from the vacuum, are twin beams, containing matching number of photons. The low-power, high gain phase conjugation observed experimentally by us in rubidium vapor under similar conditions indicate the feasibility of realizing a spatially broad band source of squeezed light, with applications to fast detection of faint images, as well as to high-density optical interconnects.