Charge-dipole-dipole interactions in cold gases

Physical Review Letters, 2008

We have observed resonant energy transfer between cold Rydberg atoms in spatially separated cylinders. Resonant dipole-dipole coupling excites the 49s atoms in one cylinder to the 49p state while the 41d atoms in the second cylinder are transferred down to the 42p state. We have measured the production of the 49p state as a function of separation of the cylinders (0 - 80 um) and the interaction time (0 - 25 us). In addition we measured the width of the electric field resonances. A full many-body quantum calculation reproduces the main features of the experiments.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2011

The behaviour of interacting ultracold Rydberg atoms in both constant electric fields and laser fields is important for designing experiments and constructing realistic models of them. In this paper, we briefly review our prior work and present new results on how electric fields affect interacting ultracold Rydberg atoms. Specifically, we address the topics of constant background electric fields on Rydberg atom pair excitation and laser-induced Stark shifts on pair excitation.

JOSA B, 2010

We review here the studies performed about interactions in an assembly of cold Rydberg atoms. We focus more specially the review on the dipole-dipole interactions and on the effect of the dipole blockade in the laser Rydberg excitation, which offers attractive possibilities for quantum engineering. We present first the various interactions between Rydberg atoms. The laser Rydberg excitation of such an assembly is then described with the introduction of the dipole blockade phenomenon. We report recent experiments performed in this subject by starting with the case of a pair of atoms allowing the entanglement of the wave-functions of the atoms and opening a fascinating way for the realization of quantum bits and quantum gates. We consider then several works on the blockade effect in a large assembly of atoms for three different configurations: blockade through electric-field induced dipole, through Förster resonance and in van der Waals interaction. The properties of coherence and cooperativity are analyzed. Finally, we treat the role of dipole-dipole interactions between Rydberg atoms responsible for Penning ionization. The perturbation of the dipole blockade by ions and the evolution of the Rydberg towards an ultracold plasma are discussed. 1 This has not to be confused with the reduced matrix element nℓ||r||n ′ ℓ ± 1 = √ 2ℓ ′ + 1C ℓ0 ℓ+10,10 nℓ|r|n ′ ℓ ± 1 , C jm j 1 m 1 ,j 2 m 2 being the standard Clebch-Gordan coefficient. For instance, with ℓ ′ = ℓ ± 1, nℓm |qez| n ′ ℓ ′ m = (ℓ+ℓ ′ +1−2m)(ℓ+ℓ ′ +1+2m) 4(2ℓ+1)(2ℓ ′ +1) R n ′ ℓ ′ nℓ , where z is the coordinate along the quantization axis.

Physical Review Letters, 1998

We studied the properties of a cold (ϳ100 mK) and dense (ϳ10 8 10 cm 23 ) atomic Rydberg Cs gas, and found that the observed widths and shapes of resonances in population transfers cannot be explained in the framework of a usual gas model. We propose a "frozen Rydberg gas" model, where the interplay between two-body and many-body phenomena affects in an unexpected way the width and the shape of spectral lines. [S0031-9007(97)04903-X] PACS numbers: 32.80.Rm, 32.80.Pj, 34.60. + z Recent demonstrations of Bose-Einstein condensation have pointed out the role of collisional processes in the evaporative cooling method [1-3]. Relatively dense cold atomic samples have revealed, in turn, a rich variety of new phenomena in atomic collision , and in particular a strong excitation exchange effect. Usually one expands the physical characteristics of a gas in the power series in density that corresponds to one-, two-, three-, etc., body phenomena. The excitation exchange is governed by the two-body interactions, whereas the many-body effects in sparse systems are usually considered as small. But does such a gas at low temperature and density remain a sparse system? In this Letter we show that the situation may change completely for an ensemble of ultracold atoms when the typical collision time considerably exceeds the time corresponding to the inverse of typical interaction energy between two neighboring atoms. In this regime the many-body phenomena play an equally important role. Observation of such phenomena becomes possible due to the recent development of a laser cooling technique, which brings new tools for atomic and molecular physics.

Journal of Physics: Conference Series, 2007

We discuss the results of measurements of the temperature and density distribution of cold Rubidium atoms trapped and cooled in an optical dipole trap formed by focussed CO2 laser beams at a wavelength of 10.6 µmfrom a cold, collimated and intense atomic beam of flux 2 × 10 10 atoms/s produced using an elongated 2D + MOT. A large number of rubidium atoms (≥ 10 10) were trapped in the MOT and the number density of atoms were further increased by making a temporal dark MOT to prevent density-limiting processes like photon rescattering by atoms at the trap centre. Subsequently, between 10 7 to 10 8 cold atoms at a temperature below 30 µK were transferred into a Quasi-Electrostatic trap (QUEST) formed by focussed CO2 laser beams at the MOT centre. Both single beam and crossed dual beam dipole traps were studied with a total output power of 50 W from the CO2 laser with focal spot sizes less than 100 microns. Various measurements were done on the cold atoms trapped in the dipole trap. The total atom number in the dipole trap and the spatial atom number density distribution in the trap was measured by absorption imaging technique. The temperature was determined from time-of-flight (TOF) data as well as from the absorption images after ballistic expansion of the atom cloud released from the dipole trap. The results from measurements are used to maximize the initial phase-space density prior to forced evaporative cooling to produce a Bose-Einstein Condensate.

Physical Review A, 2014

Helium atoms in Rydberg states have been manipulated coherently with microwave radiation pulses near a gold surface and near a superconducting NbTiN surface at a temperature of 3 K. The experiments were carried out with a skimmed supersonic beam of metastable (1s) 1 (2s) 1 1 S0 helium atoms excited with laser radiation to np Rydberg levels with principal quantum number n between 30 and 40. The separation between the cold surface and the center of the collimated beam is adjustable down to 250 µm. Short-lived np Rydberg levels were coherently transferred to the long-lived ns state to avoid radiative decay of the Rydberg atoms between the photoexcitation region and the region above the cold surfaces. Further coherent manipulation of the ns Rydberg levels with pulsed microwave radiation above the surfaces enabled measurements of stray electric fields and allowed us to study the decoherence of the atomic ensemble. Adsorption of residual gas onto the surfaces and the resulting slow build-up of stray fields was minimized by controlling the temperature of the surface and monitoring the partial pressures of H2O, N2, O2 and CO2 in the experimental chamber during the cool-down. Compensation of the stray electric fields to levels below 100 mV/cm was achieved over a region of 6 mm along the beam-propagation direction which, for the 1770 m/s beam velocity, implies the possibility to preserve the coherence of the atomic sample for several microseconds above the cold surfaces.

Tesis para optar al grado de Magister en Ciencia con Mención en Física.

Lecture Notes in Physics, 2002

The modification of the properties of a Bose-Einstein or a Fermi-Dirac atomic gas due to laser-induced dipole-dipole interactions between the atoms are considered. Nearly-isotropic illumination of the sample by spectrally-fluctuating laser beams averages out the static r −3 dipole-dipole interaction, leaving the retarded r −1 "selfgravitating" attraction in the near zone. The analogies of ultracold many-atom systems, self-bound by such laser-induced "gravity", with compact stars ("Bose stars" or "White Dwarfs") are emphasized. Even a single plane-wave laser induces dipole-dipole interactions capable of causing a cigar-shaped Bose condensate to exhibit self binding and density modulations.

2021

We study ultracold long-range collisions of heteronuclear alkali-metal dimers with a reservoir gas of alkali-metal Rydberg atoms in a two-photon laser excitation scheme. In a low density regime where molecules remain outside the Rydberg orbits of the reservoir atoms, we show that the two-photon photoassociation (PA) of the atom-molecule pair into a long-range bound trimer state is efficient over a broad range of atomic Rydberg channels. As a case study, we obtain the PA lineshapes for the formation of trimers composed of KRb molecules in the rovibrational ground state and excited Rb atoms in the asymptotic Rydberg levels nSj and nDj , for n = 20 − 80. We predict atommolecule binding energies in the range 10− 10 kHz for the first vibrational state below threshold. The average trimer formation rate is order 10 s−1 at 1.0 μK, and depends weakly on the principal quantum number n. Our results set the foundations for a broader understanding of exotic long range collisions of dilute molecu...

2008

We report clear evidence of the role of dipole-dipole interaction in Penning ionization of Rydberg atoms, leading to the formation of an ultracold plasma. Penning ionization of np Rydberg Cesium atoms is prevented for states with in n < 42, which correspond to a repulsive potential, but it does not occur for n larger than 42, corresponding to an attractive potential. Blackbody radiation is mostly responsible for the background and initial ionization, although ion-Rydberg collisions and population transfer due to limited superradiance may have to be considered.

Journal of Physics B: Atomic, Molecular and Optical Physics, 2019

We calculate pair potential curves for interacting Rydberg atoms in a constant electric field and use them to determine the effective C 3 dipole-dipole and C 6 van der Waals coefficients. We compare the C 3 and C 6 with experiments where the angle of a polarizing electric field is varied with respect to the axis of a quasi-1-dimensional trap at ultracold temperatures. The dipoles produced via polarization of the atoms have an angular dependent dipole-dipole interaction. We focus on the interaction potential of two rubidium Rydberg atoms in 50S 1/2 states in the blockade regime. For internuclear distances close to the blockade radius, R bl ≈ 4 − 6 µm, molecular calculations are in much better agreement with experimental results than those based on the properties of single atoms and independent calculations of C 3 and C 6 which were used to analyze the original experiment. We find that the calculated C 6 coefficient is within 8% of the experimental value while the C 3 coefficient is within 20% of the experimental value.

Physical Review A

Charge dynamics in an ultra-cold setup involving a laser dressed atom and an ion is studied here. This transfer of charge is enabled through molecular Rydberg states that are accessed via a laser. The character of the charge exchange crucially depends on the coupling between the electronic dynamics and the motional dynamics of the atoms and ion. The molecular Rydberg states are characterized and a criterion for distinguishing coherent and incoherent regimes is formulated. Furthermore the concept is generalized to the many-body setup as the ion effectively propagates through a chain of atoms. Aspects of the transport such as its direction can be controlled by the excitation laser. This leads to new directions in the investigation of hybrid atom-ion systems that can be experimentally explored using optically trapped strontium atoms.

2006

Physical Review Letters, 2016

We present spectroscopy of a single Rydberg atom excited within a Bose-Einstein condensate. We not only observe the density shift as discovered by Amaldi and Segrè in 1934 [1], but a line shape which changes with the principal quantum number n. The line broadening depends precisely on the interaction potential energy curves of the Rydberg electron with the neutral atom perturbers. In particular, we show the relevance of the triplet p-wave shape resonance in the e-Rb(5S) scattering, which significantly modifies the interaction potential. With a peak density of 5.5×10 14 cm-3 , and therefore an inter-particle spacing of 1300 a 0 within a Bose-Einstein condensate, the potential energy curves can be probed at these Rydberg ion-neutral atom separations. We present a simple microscopic model for the spectroscopic line shape by treating the atoms overlapped with the Rydberg orbit as zero-velocity, uncorrelated, point-like particles, with binding energies associated with their ion-neutral separation, and good agreement is found.

Physical Review Letters, 1998