We report the observation of cold Cs Rydberg atom molecules bound at internuclear separations of R ∼3-9 µm. The bound states result from avoided crossings between Rydberg atom pair interaction potentials in an applied electric field. The molecular states can be modified by changing the applied electric field. The molecules are observed by mapping the radial separation of the two Rydberg atoms as a function of time delay between excitation and detection using the Coulomb repulsion of the ions after pulsed field ionization. Measurements were performed for 63D + 65D, 64D + 66D, 65D + 67D, and 66D + 68D pairs. The experiment is in good agreement with calculations of the pair interactions for these states. PACS numbers: 34.50.Cx,32.80.Ee,82.20.Bc Frozen Rydberg gases [1,2] have been the subject of intense research recently. The construction of fast quantum gates and single photon sources using dipole blockade [3,4,5,6,7,8,9,10], the study of cold Rydberg atom molecules [11,12,13,14], and the investigation of many body physics [1,2] are central motivations for this work. Cold Rydberg atom molecules are exciting because of the interesting properties that these objects possess. Molecules formed by two cold Rydberg atoms are called macrodimers since the atoms are bound at distances > 1 µm. It has been suggested that due to their delicate nature, macrodimers can be used to study vacuum fluctuations, quenching in ultracold collisions [12] and Rydberg atom interactions including their controllability with applied electric fields. Prior experiments have been unable to unambiguously confirm that these unique states of matter exist as bound states [15,16]. We report the first experimental observation of bound macrodimers which have one of the largest, if not the largest, molecular bond observed to date.The macrodimers that we observe result from avoided crossings between Rydberg atom pair interaction potentials in an applied electric field, ǫ [13]. These FIG. 1: Integrated atomic ion yield spectra and pair potentials for 65D + 67D with ǫ = 190 mV cm −1 . The excitation laser intensity is ∼ 500 W cm −2 . All fine structure and Ω are plotted. Ω = mj1+mj2 is the projection of the angular momentum on R. The dashed line highlights one of the features studied in this paper. macrodimers are unique because they feature a quasicontinuum of bound states, are found at extremely large internuclear separation, R ∼3-9 µm, and are formed by the interplay between Van der Waals interactions and the Stark effect resulting from ǫ. ǫ can be used to stabilize, destroy or modify the potential well that gives rise to the bound states. A spectrum and calculated potentials [17] for the 65D + 67D pair with ǫ = 190 mV cm −1 , are shown in Fig. 1. The potentials have prominent wells at R ∼3-9 µm. These potential wells support hundreds of bound states [13] with maximum energy spacings of ∼100 kHz. The lifetimes of the molecules are limited by the radiative and blackbody decay of the atoms [13]. DETECTING MACRODIMERSMacrodimers are difficult to detect. P...
We observe ultralong-range blueshifted Cs(2) molecular states near ns(1/2) Rydberg states in an optical dipole trap, where 31≤n≤34. The accidental near degeneracy of (n-4)l and ns Rydberg states for l>2 in Cs, due to the small fractional ns quantum defect, leads to nonadiabatic coupling among these states, producing potential wells above the ns thresholds. Two important consequences of admixing high angular momentum states with ns states are the formation of large permanent dipole moments, ~15-100 Debye, and accessibility of these states via two-photon association. The observed states are in excellent agreement with theory.
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.
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