Rydberg aggregates

Abstract

We review Rydberg aggregates, assemblies of a few Rydberg atoms exhibiting energy transport through collective eigenstates, considering isolated atoms or assemblies embedded within clouds of cold ground-state atoms. We classify Rydberg aggregates, and provide an overview of their possible applications as quantum simulators for phenomena from chemical or biological physics. Our main focus is on flexible Rydberg aggregates, in which atomic motion is an essential feature. In these, simultaneous control over Rydberg-Rydberg interactions, external trapping and electronic energies, allows Born-Oppenheimer surfaces for the motion of the entire aggregate to be taylored as desired. This is illustrated with theory proposals towards the demonstration of joint motion and excitation transport, conical intersections and non-adiabatic effects. Additional flexibility for quantum simulations is enabled by the use of dressed dipole-dipole interactions or the embedding of the aggregate in a cold gas or BEC environment. Finally we provide some guidance regarding the parameter regimes that are most suitable for the realization of either static or flexible Rydberg aggregates based on Li or Rb atoms. The current status of experimental progress towards enabling Rydberg aggregates is also reviewed.

Transport on flexible Rydberg aggregates using circular states

“…A setup as in FIG. 1(c) realizes a Rydberg aggregate [1]. Since the number of excitations is conserved, we can describe the aggregate in the basis | π n = | aa · · · b · · · aa , where only the n'th atom is in the nextto-circular state | b and all others are in | a .…”

“…To describe a flexible aggregate with mobile atoms we solveĤ eff (X)| ϕ n (X) = U n (X)| ϕ n (X) (6) and obtain the excitonic Born-Oppenheimer surfaces U n (X) that govern the atomic motion, see [1].…”

“…With interactions determined, we can follow the approach taken in [1], to delineate parameter regimes in which circular flexible or static Rydberg aggregates are viable, based on a variety of requirements that are listed in detail in appendix D. The results are shown in FIG. 4.…”

“…Flexible aggregates: For flexible aggregates, we assume an equidistant chain with spacing d, but the existence of a dislocation on the first two atoms with spacing of only d ini = a = d/2 to initiate directed motion, similar to section V. Hence, d ini > d min must be fullfilled, a tighter constraint than d > d min . We can then assess as in [1] whether an excitation transporting pulse can traverse the chain within the system lifetime.…”

“…We refer to flexible Rydberg aggregates as assemblies of Rydberg atoms that exhibit excitation transport or collective exciton states and are mobile in a possibly restricted geometry [1]. They exhibit links between motion, excitation transport and coherence [2][3][4][5] and spatially inflated Born-Oppenheimer surfaces for the simulation of characteristic phenomena from the nuclear dynamics of complex molecules [6][7][8][9][10].…”