The resonant transfer of energy from the inversion sublevels in NH 3 to He atoms in triplet Rydberg states with principal quantum number n = 38 has been controlled using electric fields below 15 V/cm in intrabeam collisions at translational temperatures of ∼1 K. The experiments were performed in pulsed supersonic beams of NH 3 seeded in He at a ratio of 1:19. The He atoms were prepared in the metastable 1s2s 3 S 1 level in a pulsed electric discharge in the trailing part of the beams. The velocity slip between the heavy NH 3 and the lighter metastable He was exploited to perform collision studies at center-of-mass collision speeds of ∼70 m/s. Resonant energy transfer in the atom–molecule collisions was identified by Rydberg-state-selective electric-field ionization. The experimental data have been compared to a theoretical model of the resonant dipole–dipole interactions between the collision partners based on the impact parameter method.
The resonant transfer of energy from the inversion sublevels in NH 3 to He atoms in triplet Rydberg states with principal quantum number n = 38 has been controlled using electric fields below 15 V/cm in intrabeam collisions at translational temperatures of ∼1 K. The experiments were performed in pulsed supersonic beams of NH 3 seeded in He at a ratio of 1:19. The He atoms were prepared in the metastable 1s2s 3 S 1 level in a pulsed electric discharge in the trailing part of the beams. The velocity slip between the heavy NH 3 and the lighter metastable He was exploited to perform collision studies at center-of-mass collision speeds of ∼70 m/s. Resonant energy transfer in the atom–molecule collisions was identified by Rydberg-state-selective electric-field ionization. The experimental data have been compared to a theoretical model of the resonant dipole–dipole interactions between the collision partners based on the impact parameter method.
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.
Electric-field-controlled F\"orster-resonance energy transfer (FRET) between Rydberg helium (He) atoms and ground-state ammonia (NH3) molecules has been studied at translational temperatures below 100 mK. The experiments were performed in an intrabeam collision apparatus with pulsed supersonic beams of NH3 seeded in He. A range of F\"orster resonances, between triplet Rydberg states in He with principal quantum numbers of 38, 39, and 40, and the inversion intervals in NH3 were investigated. Resonance widths as low as $100\ifmmode\pm\else\textpm\fi{}20$ MHz were observed for Rydberg-Rydberg transitions with electric dipole transition moments of 3270 D. These widths result from binary collisions at a mean center-of-mass speed of $19.3\ifmmode\pm\else\textpm\fi{}2.6$ m/s. For transitions in which the initially prepared Rydberg states were strongly polarized, with large induced static electric dipole moments, van der Waals interactions between the collision partners increased the resonance widths to $\ensuremath{\sim}750$ MHz. From measurements of the rate of FRET for the narrowest resonances observed, a density of NH3 of $(9.4\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ in the upper ground-state inversion sublevel in the interaction region of the apparatus was determined nondestructively.
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 present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH3 in the X1A1 ground electronic state to helium atoms in 1sns 3S1 Rydberg levels, where n = 37 and n = 40. For these values of n, the 1sns 3S1 → 1snp 3PJ transitions in helium lie close to resonance with the ground-state inversion transitions in NH3 and can be tuned through resonance using electric fields of less than 10 V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the 3S1 and 3PJ Rydberg levels and by monitoring the population of the 3DJ levels following pulsed microwave transfer from the 3PJ levels. Detection by microwave spectroscopic methods represents a highly state selective, low-background approach to probing the collisional energy transfer process and the environment in which the atom-molecule interactions occur. The experimentally observed electric-field dependence of the resonant energy transfer process, probed both by direct electric field ionization and by microwave transfer, agrees well with the results of calculations performed using a simple theoretical model of the energy transfer process. For measurements performed in zero electric field with atoms prepared in the 1s40s 3S1 level, the transition from a regime in which a single energy transfer channel can be isolated for detection to one in which multiple collision channels begin to play a role has been identified as the NH3 density was increased.
We demonstrated a tuned dipole interaction between Rydberg atoms by employing a controllable electric field in a cold cesium ensemble. The | n P 3/2 ⟩ ( n = 38–40) Rydberg pairs are prepared with a three-photon scheme and detected via the state-selective field ionization technique. A weak DC electric field is used to tune the Rydberg pair interaction from the van der Waals interaction regime to the dipole–dipole interaction regime. The Förster resonant interaction and an adiabatic resonance energy transfer between the n P and n S Rydberg states are attained by precisely tuning the electric field. Rydberg excitation blockade with and without the electric field is investigated by changing the excitation pulse duration, which demonstrates that the dipole interaction–induced blockade effect is stronger than the van der Waals interaction–induced blockade effect. The precise control of the Rydberg interaction is of great significance to the coherent interaction in many-body systems and non-radiative collision processes.
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.