Photoassociation of Long-RangenDRydberg Molecules

Abstract

We observe long-range homonuclear diatomic nD Rydberg molecules photoassociated out of an ultracold gas of 87 Rb atoms for 34≤ n ≤40. The measured ground-state binding energies of 87 Rb(nD − 5S 1/2 ) molecular states are larger than those of their 87 Rb(nS − 5S 1/2 ) counterparts, showing the dependence of the molecular bond on the angular momentum of the Rydberg atom. We exhibit the transition of 87 Rb(nD − 5S 1/2 ) molecules from a molecular-binding-dominant regime at low n to a fine-structure-dominant regime at high n [akin to Hund's cases (a) and (c), respectively]. In the analysis the fine structure of the nD Rydberg atom and the hyperfine structure of the 5S 1/2 atom are included.PACS numbers: 34.50. Cx,34.20.Cf,33.80.Rv,31.10.+z, Cold atomic systems have opened new frontiers at the interface of atomic and molecular physics. Of particular interest are a recently discovered class of long-range, homonuclear Rydberg molecules [1,2]. Formed via an attractive interaction between a Rydberg electron and a ground-state atom [1], these molecules are among the largest ever observed with internuclear separations of several thousand Bohr radii. Their distinctive binding mechanism, which is unlike conventional covalent, ionic, and van der Waals bonds between ground-state atoms, results in loosely bound molecules whose properties closely mimic those of their constituent Rydberg atoms. The discovery of these molecular bonds has been likened to a new ultracold chemistry [3], and has spurred a significant amount of theoretical [4,5] and experimental interest [6][7][8][9]. Non-degenerate, low angular momentum Rydberg states (orbital angular momentum ℓ ≤ 2 in rubidium) produce molecules with a few tens of MHz binding energies and permanent electric dipole moments of a few Debye. The ℓ = 0 molecules were first observed by photoassociation [10] The relevant interaction was first described by Fermi [11] to help explain pressure-induced energy shifts of Rydberg absorption lines in a gas [12]. The deBroglie wavelength of the Rydberg electron (position r) is much larger than that of a heavy ground-state atom (position R) that lies within the Rydberg atom's volume, and their interaction can be approximated as a low-energy s-wave scattering process (scattering length a s ). The interaction is described with a Fermi-type pseudopotential [1,13], V pseudo (r) = 2πa s δ 3 (r − R), where p-wave and higherorder scattering [4] are neglected. For negative a s the interaction can lead to bound molecular states [1,13].In the present work we focus on long-range 87 Rb 2 molecules formed by an nD Rydberg and a 5S 1/2 ground state atom. The binding energies generally increase with ℓ, due to the √ 2ℓ + 1-scaling of the Y m=0 l (θ = 0). Among the low-ℓ variety of these molecules the nD ones have the highest binding energies. The angular-momentum coupling spans three Hund's cases when varying ℓ from 0 to 2. The nS 1/2 − 5S 1/2 molecules are akin to Hund's case (b), because they have L = 0 and total electron spin S = 1. The nP j − 5S 1/2 molecules a...

Experimental Characterization of Singlet Scattering Channels in Long-Range Rydberg Molecules

“…(2) mix the neighboring np and (n−1)d Rydberg states and induce an electric dipole moment in the molecular frame [9,11,29]. For the 32p 3/2 ,6s 1/2 (F =4 for |Ω tot | between 1/2 and 7/2.…”

Ultra-long-range Rydberg molecules in a divalent atomic system

“…Ultralong-range molecules were originally predicted theoretically [1] and were subsequently observed in Rb [2] and Cs [4]. The original observations were of dimers involving spherically symmetric S Rydberg states [2], but now measurements have been extended to anisotropic P [5,6] and D [7,8] Rydberg states and to molecules comprising one Rydberg atom and as many as four ground state atoms [9]. Excitation of Rb(nD) [9] and Cs(nP ) [6] Rydberg molecules has revealed considerable spectral complexity due to the Rydberg electron spin-orbit and ground-state hyperfine interactions, which results in mixing of singlet and triplet electronic symmetries.…”

Adiabatic potential-energy curves of long-range Rydberg molecules: Two-electronR-matrix approach

“…Later, Hamilton et al [8] in their theoretical work predicted that another class of long-range Rydberg molecular states arises when the electron interaction with the perturber exhibits a shape resonance (butterfly states). These theoretical findings were experimentally verified [9,10] and they have been the focus of numerous theoretical [11][12][13][14] and experimental [15][16][17][18][19] investigations.…”

“…It is necessary to mention that more recent experimental works [16,18,19] focus on the energies corresponding to n ≈ 35 . .…”