EIT in V+ inverted $\Xi$ system using Rydberg state in thermal Rb atoms

Rydberg excitation using blue and IR transition is an advantageous path for quantum computation in alkali elements. Aiming to stabilize the IR laser for quantum computation, we study electromagnetically induced transparency (EIT) spectrum using Rydberg state in V+inverted $\Xi$ system (${5S_{1/2}}$ $\rightarrow$ ${5P_{3/2}}$ and ${5S_{1/2}}$ $\rightarrow$ ${6P_{1/2}}$ $\rightarrow$ ${r=69D_{3/2}}$) in Rb vapour cell at room temperature. The probe laser absorption at 780 nm is monitored in the presence of the two control lasers at 421 nm and 1003 nm. In comparison to the previously studied inverted $\Xi$ system, this system has a good signal-to-noise ratio even at room temperature with similar linewidth (around $10$~MHz). We also observe Autler-Towns splitting of the EIT due to the high power of probe and blue control lasers. For completeness and comparison, we also study the EIT in an inverted $\Xi$ system using $5S_{1/2}\rightarrow6P_{1/2}\rightarrow 69D_{3/2}$ transitions.