The storage and manipulation of Rydberg atoms in traps opens up new frontiers in atomic physics, including high-precision measurements, field sensing and quantum information processing. After a brief introduction I will provide a summary of three of our recent activities in this field.
(1) Spatial correlations between Rydberg atoms in an optical
The so-called Rydberg excitation blockade plays a crucial role in experiments that involve Rydberg-Rydberg interactions. Here, we use direct spatial ion imaging to measure the Rydberg-Rydberg correlation function, with and without light-shift potentials generated by an optical dipole trap.We find an excitation blockade radius that depends on laser detunings and spatially-varying light shifts. At certain laser detunings the probability of exciting Rydberg atoms at particular separations is enhanced, which we interpret to be a result of direct two-photon excitation of Rydberg-atom pairs. The results are in accordance with predictions elsewhere and our model that accounts for a one-dimensional dipole-trap potential.
(2) Ionization of Rydberg atoms by standing-wave light fields.
When electromagnetic radiation induces transitions between atomic states, the size of the atom is usually much smaller than the wavelength of the radiation, allowing the spatial variation of the radiation field's phase to be neglected (electric-dipole approximation). Somewhat unexpectedly, the approximation is still valid for photo-ionization of Rydberg atoms in laser traps, where the atom size is on the order of the wavelength. We use a standing-wave light field as a spatially-resolving probe within the atomic volume to show that the photoionization process does not occur where the Rydberg electron is most likely to be found, but only near the nucleus, within a volume that is small with respect to the wavelength of the light field. The evidence resolves the apparent inconsistency in the electric-dipole approximation's validity in this case.
(3) Production and trapping of cold circular Rydberg atoms in a magnetic trap.
Laser-excited Rydberg atoms are circularized using the “crossed-field” method (which I will briefly explain). The trapped circular atoms are then characterized using spatial imaging and state-selective electric-field ionization. At room temperature, we observe about 70% of the trapped atoms remaining after 6 milliseconds. Measuring the trap oscillation frequency, we determine the magnetic moment of the atoms, which is the largest of any atom ever trapped. Simulations of the center-of-mass and internal-state evolution of circular atoms in the magnetic trap are in quite good agreement with experimental observations.