Nonadiabatic dynamics in Rydberg gases with random atom positions

Ritesh Pant, Rajat Agrawal, Sebastian Wüster, and Jan-Michael Rost

Phys. Rev. A 104, 063303 – Published 2 December 2021

Abstract

Assemblies of highly excited Rydberg atoms in an ultracold gas can be set into motion by a combination of van der Waals and resonant dipole-dipole interactions. Thereby, the collective electronic Rydberg state might change due to nonadiabatic transitions, in particular if the configuration encounters a conical intersection. For the experimentally most accessible scenario, in which the Rydberg atoms are initially randomly excited in a three-dimensional bulk gas under blockade conditions, we numerically show that nonadiabatic transitions can be common when starting from the most energetic repulsive Born-Oppenheimer surface. We outline how this state can be selectively excited using a microwave resonance, and demonstrate a regime where almost all collisional ionization of Rydberg atoms can be traced back to a prior nonadiabatic transition. Since Rydberg ionization is relatively straightforward to detect, the excitation and measurement scheme considered here renders nonadiabatic effects in Rydberg motion easier to demonstrate experimentally than in scenarios considered previously.

Received 27 June 2021
Accepted 3 November 2021

DOI:https://doi.org/10.1103/PhysRevA.104.063303

Physics Subject Headings (PhySH)

Cold atoms & matter waves

Rydberg atoms & molecules

Quantum correlations, foundations & formalism

Atomic, Molecular & Optical

Authors & Affiliations

Ritesh Pant ¹, Rajat Agrawal², Sebastian Wüster ¹, and Jan-Michael Rost ²

¹Department of Physics, Indian Institute of Science Education and Research, Bhopal, Madhya Pradesh 462 066, India
²Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Strasse 38, 01187 Dresden, Germany

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Issue

Vol. 104, Iss. 6 — December 2021

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Images

Figure 1
Sketch of a randomly distributed assembly of Rydberg atoms (spherical balls) in a 3D bulk gas (gray shade) at locations $r_{1}, \dots, r_{6}$ . $R_{b l}$ is the blockade radius shown by the smaller transparent sphere, representing the initial minimal distance. After passing through a conical intersection (double cones) or region of strong nonadiabatic coupling, atomic repulsion can be overcome and the collision of two Rydberg atoms (here, 4 and 5) results in ionization.
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Figure 2
Electronic and motional Rydberg dynamics for the system prepared in the highest-energy electronic state. (a),(b) Trajectory without nonadiabatic transition. (c),(d) Trajectory with nonadiabatic transition. (a) Initial configuration (colored balls) and trajectories (solid lines) of the atomic positions $r_{k} (t)$ . Colored circles and dashed lines show the projection of initial positions and trajectories onto the XY plane. (b) Time evolution of potential energies $U_{k} [R (t)]$ and the minimum distance $d_{min}$ between atoms (thick gray line, right axis) without nonadiabatic coupling. $d_{i o n}$ is the ionization distance defined in Eq. (14) (gray dotted line). (c) Adiabatic populations on the four highest-energy repulsive surfaces, showing nonadiabatic dynamics. (d) Time evolution of potential energies $U_{k} [R (t)]$ similar to (b). The presently propagated surface $s$ in Eq. (6) is shown as a red dashed line, and the three highest potential energies and $d_{i o n}$ are color coded as in (c).
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Figure 3
The same as Fig. 2, but starting from the the second most energetic electronic eigenstate $k = 17$ , instead of the highest energy one $k = 18$ .
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Figure 4
(a) Probability distribution $ρ_{k}$ of energies $U_{k}$ , $1 \leq k \leq 18$ , for 5000 random configurations ( $R)$ of atoms. We show a zoom on the high-energy flank in (b) and (c), together with a certain microwave line profile $P_{r}$ (thick red line) with detuning (b) $Δ = 120$ and (c) $Δ = 200$ MHz, respectively. The inset shows the resultant surface index distribution after excitation, according to Eq. (13).
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Figure 5
Mean time-resolved potential energy density on the (a) second, (b) third, and (c) fourth most energetic BO surface, starting with the microwave detuned to $Δ = 200$ MHz so that the system most likely begins on the first surface. To emphasize low-density features, we plot the square root of the energy densities and adjust the color bar range. The insets show (a) the relative initial excitation probability of each surface, (b) adiabatic populations, and (c) the mean number of ions per trajectory as a function of time.
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Figure 6
Mean time-resolved potential energy density similar to Fig. 5, but for the microwave detuning of $Δ = 120$ MHz, such that more surfaces are populated initially.
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