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.A Rydberg atom excited in a dense background gas of atoms provides a testbed of Rydberg electron-neutral atom collisions. Spectroscopy has always been a sensitive technique for studying these collisions and in particular spectroscopy performed in a cold, dense atom sample eliminates most other line broadening mechanisms, thereby isolating the effects of elastic and inelastic electron-neutral atom collisions on the line shape. The realization of ultralong-range Rydberg molecules via elastic electronneutral collisions [2] relies on cold, dense atom samples. Since the first observation [3], Rydberg molecules continue to be realized with increasing experimental control in various potential energy landscapes and atomic species [3][4][5][6][7][8][9][10], where the neutral atom ground state wavefunction is typically bound in the outer one or two potential wells of the electron-atom potential energy curves (PECs). By applying an electric field [11] or by exciting nS states with nearly integer quantum defects, as in Cs [12], more deeply bound trilobite Rydberg molecules [2] are realized. With higher densities of cold atom samples, many neutral atoms overlap with the Rydberg orbit and the bound states become unresolvable [13,14]. By utilizing the high densities of a Bose-Einstein condensate (BEC), the neutral atoms within the Rydberg orbit provide a probe of elastic and inelastic electron-neutral collisions for a large range of ion-neutral separations. We show in this paper that Rydberg spectroscopy in a BEC allows us to probe, with high resolution, the scattering resonance directly for the first time in this temperature regime.In a completely different temperature regime (> 400 K) than the work presented here (< 1 µK), Rydberg spectroscopy done during the 1980s in unpolarized thermal vapors investigated the line shift and line broadening of Rydberg atoms excited in a background gas of the same species atoms at similar densities [15,16]. Subsequent theory work [17][18][19][20] modeled the line shapes b...

Within a dense environment (ρ ≈ 10 14 atoms=cm 3 ) at ultracold temperatures (T < 1 μK), a single atom excited to a Rydberg state acts as a reaction center for surrounding neutral atoms. At these temperatures, almost all neutral atoms within the Rydberg orbit are bound to the Rydberg core and interact with the Rydberg atom. We have studied the reaction rate and products for nS 87 Rb Rydberg states, and we mainly observe a state change of the Rydberg electron to a high orbital angular momentum l, with the released energy being converted into kinetic energy of the Rydberg atom. Unexpectedly, the measurements show a threshold behavior at n ≈ 100 for the inelastic collision time leading to increased lifetimes of the Rydberg state independent of the densities investigated. Even at very high densities (ρ ≈ 4.8 × 10 14 cm −3 ), the lifetime of a Rydberg atom exceeds 10 μs at n > 140 compared to 1 μs at n ¼ 90. In addition, a second observed reaction mechanism, namely, Rb þ 2 molecule formation, was studied. Both reaction products are equally probable for n ¼ 40, but the fraction of Rb þ 2 created drops to below 10% for n ≥ 90.

A light, compact optical isolator using an atomic vapor in the hyperfine Paschen-Back regime is presented. Absolute transmission spectra for experiment and theory through an isotopically pure 87 Rb vapor cell show excellent agreement for fields of 0.6 T. We show π/4 rotation for a linearly polarized beam in the vicinity of the D 2 line and achieve an isolation of 30 dB with a transmission > 95 %.

The exceptionally large polarizability of highly excited Rydberg atoms—six orders of magnitude higher than ground-state atoms—makes them of great interest in fields such as quantum optics, quantum computing, quantum simulation and metrology. However, if they are to be used routinely in applications, a major requirement is their integration into technically feasible, miniaturized devices. Here we show that a Rydberg medium based on room temperature caesium vapour can be confined in broadband-guiding kagome-style hollow-core photonic crystal fibres. Three-photon spectroscopy performed on a caesium-filled fibre detects Rydberg states up to a principal quantum number of n=40. Besides small energy-level shifts we observe narrow lines confirming the coherence of the Rydberg excitation. Using different Rydberg states and core diameters we study the influence of confinement within the fibre core after different exposure times. Understanding these effects is essential for the successful future development of novel applications based on integrated room temperature Rydberg systems.