Excitation of Weakly Bound Molecules to Trilobitelike Rydberg States

Abstract

We observe "trilobite-like" states of ultracold 85 Rb2 molecules, in which a ground-state atom is bound by the electronic wavefunction of its Rydberg-atom partner. We populate these states through the ultraviolet excitation of weakly-bound molecules, and access a regime of trilobite-like states at low principal quantum numbers and with vibrational turning points around 35 Bohr radii. This demonstrates that, unlike previous studies that used free-to-bound transitions, trilobite-like states can also be excited through bound-to-bound transitions. This approach provides high excitation probabilities without requiring high-density samples, and affords the ability to control the excitation radius by selection of the initial-state vibrational level.PACS numbers: 33.80. Rv, 33.20.Lg, 31.10.+z A class of long-range Rydberg molecules, sometimes called "trilobite molecules," occurs when a ground-state atom is embedded within the electronic wavefunction of a Rydberg atom [1]. The bond between the Rydberg atom and the ground-state atom originates from the attractive interaction between the Rydberg electron and the ground-state atom [1]. This bond has been described as a new type of chemical bond, distinct from the wellknown covalent, ionic, and van der Waals bonds [2]. The name "trilobite molecule" was coined because in certain states, the perturbed Rydberg-electron wavefunction resembles a trilobite fossil [1]. Trilobite states are characterized by large, and degenerate, values of orbital angular momentum (l ≥ 3) and large permanent electric dipole moments (EDMs ∼ 1 kDebye). Although pure trilobite states have yet to be observed, trilobite-like states, bound by the same novel chemical bond but characterized primarily by lower values of l and smaller EDMs, have been observed at ultracold temperature in photoassociation to bound vibrational levels [3][4][5][6][7][8], and at high temperatures in the form of satellite structures in the wings of atomic transitions [9,10].We adopt the name "trilobite-like" molecules for the low-l states to distinguish them from other types of longrange Rydberg molecules, such as macrodimers [11][12][13] or heavy Rydberg atoms [14,15].The bond length of a trilobite-like molecule can vary greatly depending on the principal quantum number, due to the n 2 dependence of the radius of the outermost lobe of the Rydberg wavefunction. For instance, the vibrational outer turning points of trilobite-like molecules have ranged from below 150 Bohr radii (a 0 ) in Refs. [9, 10] to above 10 3 a 0 in Refs. [3][4][5][6][7][8].Here we report the observation of trilobite-like states of 85 Rb 2 by a new method. We start by producing ultracold Rb 2 molecules in a high vibrational level of the metastable a 3 Σ + u state via photoassociation of atoms in a magneto-optical trap (MOT), then excite them directly to trilobite-like states, detecting them via their autoionization into Rb + 2 molecular ions. We observe these states in some of the lowest principal quantum numbers for which they can exist, n = 7 and 9-12, and...

Photoassociation of Long-RangenDRydberg Molecules

“…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.…”

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

“…corresponding to experiments [9,15,17]. This work aims to complement previous studies [9,17] and test the approximation of the contact potential at smaller internuclear distances utilized there to explain the experimental spectra.…”

“…This work aims to complement previous studies [9,17] and test the approximation of the contact potential at smaller internuclear distances utilized there to explain the experimental spectra. In order to test the basic mechanisms of the method we decided to test it on the simplest of molecules, H 2 .…”

“…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.…”

Lifetimes of ultralong-range strontium Rydberg molecules in a dense Bose-Einstein condensate

“…Initial experiments focused on creation of dimer molecules comprising a ground-state rubidium atom bound to a spherically-symmetric Rb(ns) Rydberg atom [2]. Measurements have since been extended to include other Rydberg species, anisotropic P and D Rydberg states and, using Cs(ns) Rydberg atoms, to the creation of so-called trilobite states with very large permanent electric dipole moments [3][4][5][6][7][8][9][10][11][12]. Detailed spectroscopic studies have revealed the formation of molecules comprising one Rydberg atom and up to four bound ground-state atoms [13].…”