Coherent population transfer of ground-state atoms into Rydberg states

The technique of stimulated Raman adiabatic passage (STIRAP) is used to excite laser-cooled rubidium atoms from the ${}^{85}\mathrm{Rb}5S_{1∕2}$ ground state to the $44D_{5∕2}$ Rydberg state through the $5P_{3∕2}$ state. The utilized double-STIRAP scheme allows for an accurate determination of the absolute excitation efficiency. Experimental data are compared with results of a detailed theoretical model, and good agreement is found. It is concluded that at the center of the excitation region an excitation efficiency of 70% is achieved.

Figure 1

(Color online) (a) Level diagram; (b) experimental timing diagram showing two STIRAP and field-ionization sequences. Two identical sequences, $S_1$ and $S_2$, are required to provide a reliable measure of the excitation efficiency.

Figure 2

Number of Rydberg atoms detected after the first (triangles up) and the second (triangles down) STIRAP sequence vs time delay $\Delta T$ between laser pulses for pulse durations of $0.2\mu \mathrm{s}$ (a) and $0.5\mu \mathrm{s}$ (b). The experimental results are compared with theory for a lower-transition Rabi frequency of 10 MHz and upper-transition Rabi frequencies of ${\Omega }_b^0∕\left(2\pi \right)=7.5\mathrm{MHz}$ (dashed lines) and 5 MHz (solid lines).

Figure 3

(a) Laser-induced Rydberg-atom quenching. The lower-transition red laser pulse is on from $t=0.2$ to $0.4\mu \mathrm{s}$, and the upper-transition blue laser pulse from 0 to $t$ ($x$-coordinate of the plot). Rydberg-atom quenching occurs for $t>0.4\mu \mathrm{s}$. Measurements (squares) and simulations for ${\Omega }_b^0∕\left(2\pi \right)=5$, 7.5, and 10 MHz (dot-dashed, dashed, and solid curves, respectively) are shown; (b) field ionization pulse and field-ionization spectrum for $\Delta T=0$ and laser pulse width of $0.5\mu \mathrm{s}$. The $44D$ state ionizes at $\sim 310\mathrm{V}$.

Figure 4

(Color online) Efficiency of the Rydberg-state excitation, ${\eta }_a$, vs the central Rabi frequency of the upper transition, ${\Omega }_b^0∕\left(2\pi \right)$, and distance $r$ from the center of the blue beam. The Rabi frequency of the lower transition is 10 MHz.