  Slow light based on the effect of electromagnetically induced transparency is
of great interest due to its applications in low-light-level nonlinear optics
and quantum information manipulation. The previous experiments all dealt with
the single-component slow light. Here we report the experimental demonstration
of two-component or spinor slow light using a double tripod atom-light coupling
scheme. The scheme involves three atomic ground states coupled to two excited
states by six light fields. The oscillation due to the interaction between the
two components was observed. Based on the stored light, our data showed that
the double tripod scheme behaves like the two outcomes of an interferometer
enabling precision measurements of frequency detuning. We experimentally
demonstrated a possible application of the double tripod scheme as quantum
memory/rotator for the two-color qubit. Our study also suggests that the spinor
slow light is a better method than a widely-used scheme in the nonlinear
frequency conversion.
