Rydberg atoms have a long history of scientific research, but they have recently seen a resurgence in popularity due to their advantages when dealing with coupled internal Rydberg states, or externally-coupled Rydberg atoms. The use of convenient RF and/or microwave generation techniques allows for straightforward coupling of many nearby Rydberg states, enabling quantum simulation studies, such as the generation of a synthetic lattice. Strontium is particularly attractive for Rydberg atom studies due to its optically active core, which allows for two-electron excited states and its conveniently accessible transition frequencies that match those available using commercial diode lasers. Before these experiments and applications can be realized however, precise knowledge of Rydberg state energies and quantum defects is required. Therefore, this work undertakes an extensive study of the quantum defects of both singly and doubly-excited strontium Rydberg atoms for a wide range of n and l. Precision microwave spectroscopy between nearby Rydberg states produces an improved self-consistent set of quantum defects for singly-excited 1S0, 1P1, 1D2, and 1F3 states, described by their corresponding Rydberg-Ritz parameters. Quantum defects and lifetimes for autoionizing two-electron-states are also presented. These elucidate the effects of core penetration by the “outer” excited Rydberg electron on transitions within the core ion and on the Rydberg level itself.
The short Doppler-limited coherence time of the laser-excited Rydberg state, usually orders of magnitude shorter than the lifetime of the Rydberg state, hinders the Rydberg-mediated quantum technologies. Here, we show that a 649~nm~
−~658~nm two-photon excitation of the
6sng 1G4 Rydberg state from a long-lived d-orbital clock state of barium can be achieved with a two-photon wavevector that is tiny, which effectively removes the Doppler-limited decoherence. Moreover, the
6sng 1G4 Rydberg state has strong dipole-dipole interaction due to small Förster defect with nearby Rydberg states and possesses long radiative lifetime. These can benefit quantum computing based on individually trapped neutral atoms, and can enable long-lived Rydberg polaritons in atomic media, which brings fresh opportunities in all-optical quantum information.
Atoms in highly excited Rydberg states exhibit remarkable properties such as large polarizability and strong interactions. This makes them interesting for a manifold of applications ranging from electric field sensors to carriers and mediators of quantum information and renders them into a powerful tool for studying quantum phenomena in strongly interacting many-particle systems. In this article we illuminate perspectives for the study of the relaxation and thermalization dynamics of closed many-body quantum systems using alkali atoms that are held in a ring lattice and excited to Rydberg states. Moreover, we show that Rydberg atoms confined to lattices offer exciting possibilities for the creation of entangled many-body quantum states which can serve as a resource for the generation of non-classical light.
Quantum nonlinear optics by Rydberg polaritons can enable single-photon transistor and switch, single-photon source, and deterministic quantum information processing. A major hindrance in this study is the fast motional decoherence. Here, we devise a scheme to significantly enhance the coherence of Rydberg polariton by letting the atoms {\it remember} their velocities, or, alternatively, by {\it changing} the phase of Rydberg polariton according to its storage time. After the Rydberg polariton is prepared with a Rydberg state
∣r1⟩, i.e., during the storage time, two laser fields induce a transition between
∣r1⟩ and a nearby Rydberg state
∣r2⟩ via a low-lying intermediate state
∣f⟩ which is largely detuned. In particular, we find that either a
2πN protocol, a
π-wait-
π protocol, or a wait-
π protocol, along with an appropriate choice of
∣f⟩ can lead to a phase-coherent Rydberg polariton upon its retrieval. Importantly, the coherent transition between
∣r1⟩ and
∣r2⟩ ensures that the Rydberg polariton can block the Rydberg excitation of nearby atoms as in usual applications of Rydberg polaritons. Numerics show that the theory can nearly completely eliminate the motional dephasing, leaving Rydberg-state decay as the only fundamental channel of decoherence. This sheds light on a broad application of Rydberg-mediated quantum nonlinear optics.