Coherent Population Transfer in an Atom by Multiphoton Adiabatic Rapid Passage

Coherent population transfer in an atom using a sequence of adiabatic rapid passages through single-photon resonances is well-known, but it requires that the frequency sweep match the changing frequencies of the atomic transitions. The same population transfer can be effected via a single multiphoton adiabatic rapid passage, which requires only a small frequency sweep, if it is possible to select the desired multiphoton transition from the many possible transitions. Here we report the observation of population transfer between Rydberg states by high order multiphoton adiabatic rapid passage.

Figure 1

(a) $n=72\to 82$ transition by a sequence of single-photon ARPs. (b) $n=72$ and $n=82$ Floquet states near the ten-photon resonance plotted as a function of MW frequency $\nu$ (solid curves). In zero MW field the two levels cross, as shown by the broken lines.

Figure 2

(a) Floquet energy levels as defined in Eq. (1) for $60\le n\le 84$ vs MW frequency in zero MW field. The $n=69$, 70, 71, 75, 80, and 81 levels are labeled. The $\Delta n=1$ resonances are the highest lying level crossings, and $\Delta n>1$ crossings are lower in energy. (b) With a MW amplitude of $3\mathrm{V}/\mathrm{cm}$, the $\Delta n=k$, $k\le 8$ avoided crossings become smooth curves, the $\Delta n=10$ avoided crossings are recognizable as isolated avoided-level crossings, and the $\Delta n\ge 11$ avoided crossings are invisible on this scale. $n=72–82$ ten-photon avoided crossing is denoted as A at 15.2 GHz. With a $19\to 13\mathrm{GHz}$ chirped pulse the atoms in level B pass to D through C.

Figure 3

Time-resolved field-ionization signals obtained subsequent to exposing $n=72$ atoms to a 50 ns, $+0.012\mathrm{GHz}/\mathrm{ns}$ chirped pulse centered at 15.2 GHz, so that only $\sim 600\mathrm{MHz}$ of chirp is required. For pulse amplitude zero (dashed line), the atoms stay in the $n=72$ state. For pulse amplitude $2\mathrm{V}/\mathrm{cm}$ (dotted line), roughly 40% of the atoms are transferred to $n\approx 83$. With pulse amplitude $3\mathrm{V}/\mathrm{cm}$ (solid line), more than 80% of the atoms are transferred to $n\approx 83$.

Figure 4

Gray-scale renderings of the final-state distributions subsequent to exposure to constant amplitude MW pulses. Each panel is built up from 26 oscilloscope traces of the field-ionization signals; $t=0$ corresponds to the beginning of the field ramp. (a) Atoms initially in $n=80$ exposed to 19 to 13 GHz chirped pulses. The calculated $\Delta n$ transfers are shown by crosses (+). Population transfer to $n$ as low as $\sim 72$ is observed. (b) Atoms initially in $n=73$ exposed to 13 to 19 GHz chirped pulses. Population transfer to $n\approx 77$ is efficient, and transfer to very high $n$ states is observed.