In situ observation of Rydberg chemistry in a coherent solvent

We experimentally demonstrate the use of a Bose-Einstein condensate (BEC) as a “tracking device” [1] for Rydberg chemistry, akin to a bubble chamber. A single ultra-long range Rydberg molecule embedded in the BEC can coherently excite waves, carrying tell-tale signatures of its dynamics. Bond lengths exceeding a micrometer allow us to observe the fingerprint of these molecules on the BEC via optical microscopy. Simulations of expected in-situ condensate images evidence that the molecular electronic state rapidly transforms from an initially excited S- or D- orbital to a complex trilobite molecular state, marked by a strongly localized electron wave function [2]. The state change liberates energy, which should cause final state particles to move rapidly through the medium, which is however ruled out by comparing experiment and simulations. The molecule thus must strongly decelerate in the medium, for which we propose a plausible mechanism. Our experiment features an ambient coherent medium that facilitates and records an electronic state change of exotic molecules in ultra-cold chemistry, with sufficient sensitivity to constrain velocities of final state products. The same platform can also provide controllable decoherence of superposition states and permit a glimpse of the environmental component of decohering entangled states [3].

[1] S. Tiwari and S. Wüster, Phys. Rev. A 99, 043616 (2019).

[2] S. Tiwari, F. Engel, M. Wagner, R. Schmidt, F. Meinert and S. Wüster, New J. Phys. 24, 073005 (2022).

F. Engel, S. Tiwari, T. Pfau, S. Wüster and F. Meinert, https://arxiv.org/abs/2308.13762 (2023).

[3] S. Rammohan et al., Phys. Rev. A (Letters) 104, L060202 (2021), Phys. Rev. A 103, 063307 (2021).