We have observed resonant-energy-transfer collisions between K Rydberg atoms. We have tuned the ${\mathrm{ns}}_{1/2}$+(n-2)${\mathrm{d}}_{\mathrm{j}}$\ensuremath{\rightarrow}${\mathrm{np}}_{\mathrm{j}\ensuremath{'}}$+(n-1)${\mathrm{p}}_{\mathrm{j}\mathrm{\ensuremath{''}}}$ collisional process into resonance with a static electric field. The measured resonance field positions from n=24 to 29 agree well with the calculated positions. We show that the dipole-dipole selection rule, \ensuremath{\Delta}${\mathrm{m}}_{\mathrm{j}}$=0,\ifmmode\pm\else\textpm\fi{}1, is valid for these resonances but that \ensuremath{\Delta}J=0,\ifmmode\pm\else\textpm\fi{}1 is not, due to the presence of the electric field. In addition, the polarization of the lasers used to excite the Rydberg states can suppress many of the resonances.
We have observed resonant-energy-transfer collisions between K Rydberg atoms. We have tuned the ns1/2+(n-2)dj\ensuremath{\rightarrow}npj\ensuremath′+(n-1)pj\ensuremath′′ collisional process into resonance with a static electric field. The measured resonance field positions from n=24 to 29 agree well with the calculated positions. We show that the dipole-dipole selection rule, \ensuremath{\Delta}mj=0,\ifmmode\pm\else\textpm\fi{}1, is valid for these resonances but that \ensuremath{\Delta}J=0,\ifmmode\pm\else\textpm\fi{}1 is not, due to the presence of the electric field. In addition, the polarization of the lasers used to excite the Rydberg states can suppress many of the resonances.
We have studied the collisional energy transfer process K (ns) +K (n-2) d {yields} K (np) +K (n-1) p which is tuned into resonance with an applied static electric field. The initial Rydberg states are excited stepwise with two dye laser pulses. The resonant energy transfer is detected by selectively field ionizing the final K(np) state as the static field is swept over many laser shots. Due to fine structure splitting of the d and p levels 45 resonances are energetically allowed at n{sub s}=25. The actual number of resonances that are observed depends on the polarization of the laser light, the dipole-dipole selection rules, and the n state excited. Above n{sub s}=29 all resonances are energically forbidden. We have measured the position of the resonances in electric field from n{sub s}=25 to n{sub s}=29 and found them to be in good agreement with calculated positions.
Resonant collisional energy transfer can be studied in uprecedented detail using Rydberg atoms. Using the dependence of the energy level spacing on principal quantum number it is possible to examine resonant energy transfer in collisions with molecules. Finer control of the level spacing is possible by varying the level spacings with an electric field. Using this approach it is possible to observe sharply resonant collisions between Rydberg atoms. They are resonant dipole-dipole collisions which have cross sections orders of magnitude larger than the geometric cross sections of the colliding Rydberg atoms. These collisions are interesting in themselves; for example, they exhibit intracollisional interference, and it is possible to know when individual collisions begin and end. Perhaps the most interesting aspect of these collisions is that, because of the large dipole moments of the Rydberg atoms, they are easily controlled by microwave and radio frequency fields.
The effects of weak electric fields on resonant energy transfer between NH3 in the X1A1 ground electronic state and Rydberg He atoms in triplet states with principal quantum numbers n=36--41 have been studied in a crossed-beam apparatus. For these values of n, electric dipole transitions between the Rydberg states that evolve adiabatically to the $|ns\ensuremath{\rangle}$ and $|np\ensuremath{\rangle}$ states in zero electric field can be tuned into resonance with the ground-state inversion transitions in NH3 using electric fields, with energy transfer occurring via F\"orster resonance. In the experiments the Rydberg He atoms, traveling in pulsed supersonic beams, were prepared by resonant two-photon excitation from the metastable 1s2s3S1 level and crossed an effusive beam of NH3 before being detected by state-selective pulsed-electric-field ionization. The resonant-energy-transfer process was identified by monitoring changes in the ionization signal from the $|ns\ensuremath{\rangle}$ and $|np\ensuremath{\rangle}$ Rydberg states for each value of n. The electric-field dependence of the experimental data is in good agreement with the results of calculations in which the resonant dipole-dipole coupling between the collision partners was accounted for.
A large enhancement in the resonant collisional energy-transfer process $\mathrm{Na}(\mathrm{ns})+\mathrm{Na}(\mathrm{ns})\ensuremath{\rightarrow}\mathrm{Na}[(n\ensuremath{-}1)p]+\mathrm{Na}(\mathrm{nl})$ or $\mathrm{Na}(\mathrm{ns})+\mathrm{Na}(\mathrm{ns})\ensuremath{\rightarrow}\mathrm{Na}(\mathrm{np})+\mathrm{Na}[(n\ensuremath{-}1)l]$ is observed when the initial ns state lies midway between $(n\ensuremath{-}1)p$ and an nl state or between np and an $(n\ensuremath{-}1)l$ state. This resonance condition, achieved by the electric field tuning of the levels, leads to large cross sections \ensuremath{\sim} 109A˚2 and narrow linewidths \ensuremath{\sim} 1 GHz. These cross sections and linewidths are comparable to the previously observed resonant process $\mathrm{Na}(\mathrm{ns})+\mathrm{Na}(\mathrm{ns})\ensuremath{\rightarrow}\mathrm{Na}[(n\ensuremath{-}1)p]+\mathrm{Na}(\mathrm{np})$. We have also observed a similar collisional energy transfer starting from a completely different initial state, i.e., $\mathrm{Na}(15d)+\mathrm{Na}(15d)\ensuremath{\rightarrow}\mathrm{Na}(16f)+\mathrm{Na}(15p)$. In this case the enhancement in the cross section (\ensuremath{\sim} 108A˚2) is observed at a relatively low electric field \ensuremath{\sim} 17 V/cm.
The large electric dipole moments associated with transitions between Rydberg states of atoms or molecules, make them ideal model systems with which to study Förster resonance energy transfer in collisions with other Rydberg atoms or molecules, or with polar ground-state molecules [1,2]. The sensitivity of high Rydberg states to electric fields allows these energy transfer processes to be tuned thorough resonance by exploiting the Stark effect. In this talk, I will describe recent experiments in which we have observed the resonant transfer of energy from the ground-state inversion sublevels in ammonia, to helium atoms in triplet Rydberg states with principal quantum numbers between 38 and 43. The experiments were performed at translational temperatures below 1 K in seeded, pulsed supersonic beams [3]. Electric fields up to ~10 V/cm were used to tune transitions between selected Rydberg states into resonance with the transitions between the inversion sublevels. Resonant energy transfer was identified by Rydberg-state-selective electric-field ionisation. The experimental data exhibit quantum-state-dependent resonance widths that range from 200 to 700 MHz and, in general, reduce as the value of the principal quantum number is increased. Comparison with the results of numerical calculations of the Rydberg energy-level structure and transition moments, shows a dependence of the measured widths on the electric dipole transition moments of the Rydberg-Rydberg transitions. These results are of particular interest, e.g., for applications in coherent control and quantum sensing [4-6], and in the study of low-temperature ion-molecule reactions performed within the orbit of a Rydberg electron [7]. [1] T. F. Gallagher, Phys. Rep. 210, 319 (1992) [2] F. B. Dunning, S. Buathong, Int. Rev. Phys. Chem. 37, 287 (2018) [3] K. Gawlas and S. D. Hogan, J. Phys. Chem. Lett. 11, 83 (2020) [4] M. Zeppenfeld, Euro. Phys. Lett. 118, 13002 (2017). [5] E. Kuznetsova, S. T. Rittenhouse, H. R. Sadeghpour, and S. F. Yelin, Phys. Rev. A 94, 032325 (2016). [6] E. Kuznetsova, S. T. Rittenhouse, H. R. Sadeghpour, and S. F. Yelin, Phys. Chem. Chem. Phys. 13, 17115 (2011). [7] K. Höveler, J. Deiglmayr, J. A. Agner, H. Schmutz and F. Merkt, Phys. Chem. Chem. Phys. 23, 2676 (2021).
We have observed the sharply resonant enhancement of the cross section of the collision process $ns+ns\ensuremath{\rightarrow}np+(n\ensuremath{-}1)p$ between two Nans (16<n<27) atoms which occurs when the levels are shifted by an electric field so that the ns level lies midway between the two p states. The widths of the collisional resonances scale as ${n}^{\ensuremath{-}2}$ and the magnitudes of the cross sections as n4, with values of 0.5 GHz and 8\ifmmode\times\else\texttimes\fi{}108A˚2 for the 20s state. These results are in good agreement with calculations based on the long-range dipole-dipole interaction between the two atoms.