Measurement of the electric quadrupole amplitude in atomic thallium 6P1/2? 6P3/2 transition using electromagnetically induced transparency

We report on a measurement of the transition amplitude ratio chi of an electric quadrupole (E2) to a magnetic dipole (M1) of the 6P(1/2) -> 6P(3/2) transition in atomic thallium. We utilized the electromagnetically induced transparency mechanism and the sideband-bridging technique to resolve the isotopic transitions and their hyperfine manifold. Our measurement gave (chi 205) = 0.2550(20)(7) for Tl-205, and (chi 203) = 0.2532(73)(7) for Tl-203, which was measured for the first time. Our results provide a reference point for the theoretical calculation of atomic structures, and new input for the long dispute on the atomic thallium parity non-conservation measurements.