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arXiv:2501.14303

Anomalies in the rotational spectra of $^{86}$Sr ULRRM dimers

C. Wang, Lu, Y., Li, A., S. K. Kanungo, T. C. Killian, F. B. Dunning, S. Yoshida

Published Jan 24, 2025• 0 citations
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Abstract

Anomalies in the rotational structure of $^{86}$Sr $^3S_1$ dimer ultralong-range Rydberg molecules (ULRRMs) created in a cold strontium gas by two-photon excitation via the intermediate $5s5p~^3P_1$ state are reported. Measurements reveal that the distribution of product rotational states is sensitive to intermediate state detuning. Comparative studies using $^{84}$Sr $^1S_0$ and $^3S_1$, and $^{86}$Sr $^1S_0$ dimers display no similar behavior, indicating that the observed behavior is peculiar to $^{86}$Sr triplet dimers. While we have no definitive hypothesis as to the physical mechanism responsible for this behavior, possible explanations might involve the very different scattering lengths for $^{84}$Sr and $^{86}$Sr, or the interchange of spin and rotational angular momentum.

DOI
10.48550/arxiv.2501.14303

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Anomalies in the rotational spectra of 86^{86}86Sr ULRRM dimers
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Anomalies in the rotational structure of 86Sr^{86}\mathrm{Sr}86Sr 3S1^{3}S_{1}3S1​ dimer ultralong-range Rydberg molecules created in a cold strontium gas by two-photon excitation via the intermediate 5s5p5s5p5s5p 3P1^{3}P_{1}3P1​ state are reported. Measurements reveal that the distribution of product rotational states is sensitive to intermediate state detuning. Comparative studies using 84Sr^{84}\mathrm{Sr}84Sr 1S0^{1}S_{0}1S0​ and 3S1^{3}S_{1}3S1​, and 86Sr^{86}\mathrm{Sr}86Sr 1S0^{1}S_{0}1S0​ dimers display no similar behavior, indicating that the observed behavior is peculiar to 86Sr^{86}\mathrm{Sr}86Sr triplet dimers. While we have no definitive hypothesis as to the physical mechanism responsible for this behavior, possible explanations might involve the very different scattering lengths for 84Sr^{84}\mathrm{Sr}84Sr and 86Sr^{86}\mathrm{Sr}86Sr, or the interchange of spin and rotational angular momentum.
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Spectroscopy of ⁸⁷Sr Rydberg Atoms and Molecules This dissertation describes the development of an apparatus to undertake spectroscopic studies of ⁸⁷Sr Rydberg states and their application in the production of ultra-long-range Rydberg molecules (ULRRMs). Most previous spectroscopic studies of strontium have been performed with the bosonic isotope ⁸⁸Sr which has no nuclear spin (I=0), resulting in a relatively simple and well-understood Rydberg excitation spectrum. In contrast, fermionic ⁸⁷Sr has a large nuclear spin (I=9/2) that leads to strong hyperfine interactions which greatly complicate the Rydberg excitation spectrum. In order to understand the Rydberg states in ⁸⁷Sr, two-photon spectroscopy was performed to measure and identify the (5sns)³S and (5snd)³D hyperfine Rydberg states for 30≲n≲99. Working with theory collaborators, a detailed understanding of how the hyperfine interaction affects the Rydberg levels is developed and used to extract revised quantum defects. The detailed understanding of the ⁸⁷Sr hyperfine Rydberg structure was exploited to produce the first ULRRMs in a fermionic gas. Unlike traditional molecular binding mechanisms, ULRRMs comprise of one or more ground-state atoms embedded in the electron cloud of a Rydberg atom with the entire system bound together through the weak Rydberg electron-neutral atom scattering. Therefore, production of ULRRMs is dependent on both the principal quantum number (n) of the parent Rydberg atom and the initial spatial distribution of atoms. At low temperatures, the effects of quantum statistics becomes important and result in bunching (bosons) and antibunching (fermions). These differences in spatial distributions can influence the excitation rates of ULRRMs. Current progress in exploring the role of quantum statistics in the excitation of ULRRMs using cold, dense strontium gases is described, with an emphasis on ⁸⁷Sr, and how such measurements can be used to extract the pair correlation function g⁽²⁾(R).
Abstract Photoexcitation rates for creation of ultralong-range Rydberg molecules with 31 ≲ n ≲ 41 in both ground and excited vibrational levels in cold ( T ∼ 900 nK) gases of polarized and unpolarized 87 Sr are presented. The measured production rates of the ν = 0, 1 and 2 vibrational levels reveal rather different n dependences which are analyzed by evaluating the Franck–Condon factors associated with excitation of the different vibrational levels and molecular rotational states. In particular, for gases of spin-polarized fermions, only Rydberg dimers with odd rotational quantum numbers are excited due to the requirement that their wave functions be anti-symmetric with respect to exchange. The data also demonstrate that measurements of the formation of vibrationally-excited ν = 1 molecules can furnish a probe of pair correlations over intermediate length scales.