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arXiv:1812.07533 · Science

Quantum gas microscopy of Rydberg macrodimers

Simon Hollerith, Johannes Zeiher, Jun Rui, Antonio Rubio-Abadal, Valentin Walther, Thomas Pohl, Dan Stamper-Kurn, Immanuel Bloch, Christian Groß

Published May 16, 2019• 68 citations
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Abstract

The subnanoscale size of typical diatomic molecules hinders direct optical access to their constituents. Rydberg macrodimers-bound states of two highly excited Rydberg atoms-feature interatomic distances easily exceeding optical wavelengths. We report the direct microscopic observation and detailed characterization of such molecules in a gas of ultracold rubidium atoms in an optical lattice. The bond length of about 0.7 micrometers, comparable to the size of small bacteria, matches the diagonal distance of the lattice. By exciting pairs in the initial two-dimensional atom array, we resolved more than 50 vibrational resonances. Using our spatially resolved detection, we observed the macrodimers by correlated atom loss and demonstrated control of the molecular alignment by the choice of the vibrational state. Our results allow for rigorous testing of Rydberg interaction potentials and highlight the potential of quantum gas microscopy for molecular physics.

DOI
10.1126/science.aaw4150

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Chemical Physics In a Rydberg state, an atom has been very nearly, but not quite, ionized. This puts the electron relatively far from the nucleus, and two atoms in such a state can thus form a rather long-range bond. Hollerith et al. observed this phenomenon in fine detail by exciting pairs of ultracold rubidium atoms along the diagonal of an optical lattice. The authors resolved the vibrational state structure spectroscopically and showed that the Rydberg dimers manifested bond lengths exceeding 700 nanometers. Science , this issue p. [664][1] [1]: /lookup/doi/10.1126/science.aaw4150

Science•May 16, 2019•0 citations
The subnanoscale size of typical diatomic molecules hinders direct optical access to their constituents. Rydberg macrodimers-bound states of two highly excited Rydberg atoms-feature interatomic distances easily exceeding optical wavelengths. We report the direct microscopic observation and detailed characterization of such molecules in a gas of ultracold rubidium atoms in an optical lattice. The bond length of about 0.7 micrometers, comparable to the size of small bacteria, matches the diagonal distance of the lattice. By exciting pairs in the initial two-dimensional atom array, we resolved more than 50 vibrational resonances. Using our spatially resolved detection, we observed the macrodimers by correlated atom loss and demonstrated control of the molecular alignment by the choice of the vibrational state. Our results allow for rigorous testing of Rydberg interaction potentials and highlight the potential of quantum gas microscopy for molecular physics.
Controlling molecular binding at the level of single atoms is one of the holy grails of quantum chemistry. Rydberg macrodimers─bound states between highly excited Rydberg atoms─provide a novel perspective in this direction. Resulting from binding potentials formed by the strong, long-range interactions of Rydberg states, Rydberg macrodimers feature bond lengths in the micrometer regime, exceeding those of conventional molecules by orders of magnitude. Using single-atom control in quantum gas microscopes, the unique properties of these exotic states can be studied with unprecedented control, including the response to magnetic fields or the polarization of light in their photoassociation. The high accuracy achieved in spectroscopic studies of macrodimers makes them an ideal testbed to benchmark Rydberg interactions, with direct relevance to quantum computing and information protocols where these are employed. This review provides a historic overview and summarizes the recent findings in the field of Rydberg macrodimers. Furthermore, it presents new data on interactions between macrodimers, leading to a phenomenon analogous to Rydberg blockade at the level of molecules, opening the path toward studying many-body systems of ultralong-range Rydberg molecules.
Long-range metastable molecules consisting of two cesium atoms in high Rydberg states have been observed in an ultracold gas. A sequential three-photon two-color photoassociation scheme is employed to form these molecules in states, which correlate to np(n+1)s dissociation asymptotes. Spectral signatures of bound molecular states are clearly resolved at the positions of avoided crossings between long-range van der Waals potential curves. The experimental results are in agreement with simulations based on a detailed model of the long-range multipole-multipole interactions of Rydberg-atom pair states. We show that a full model is required to accurately predict the occurrence of bound Rydberg macrodimers. The macrodimers are distinguished from repulsive molecular states by their behavior with respect to spontaneous ionization and possible decay channels are discussed.
Precise control and study of molecules is challenging due to the variety of internal degrees of freedom and local coordinates that are typically not controlled in an experiment.Employing quantum gas microscopy to position and resolve the atoms in Rydberg macrodimer states solves most of these challenges and enables unique access to the molecular frame.Here, we demonstrate this approach and present photoassociation studies in which the molecular orientation relative to an applied magnetic field, the polarization of the excitation light, and the initial atomic state are fully controlled.The observed dependencies allow for an electronic structure tomography of the molecular state.We additionally observe an orientation-dependent Zeeman shift, and we reveal a significant influence on it caused by the hyperfine interaction of the macrodimer state.Finally, we demonstrate control over the electrostatic binding potential by engineering a gap between two crossing pair potentials.Our results establish macrodimers as the most sensitive tool to benchmark Rydberg interaction potentials, and they open new perspectives for improving Rydberg dressing schemes.
The coupling of an isolated quantum state to a continuum is typically associated with decoherence and decreased lifetime. For coupling rates larger than the bandwidth of the associated continuum, decoherence can be mitigated, and new stable eigenstates emerge. Here, we laser-couple diatomic molecules of highly excited Rydberg atoms, so-called Rydberg macrodimers, to a continuum of free motional states. Enabled by their small vibrational eigenfrequencies, we achieve the regime of strong continuum couplings and observe the appearance of new resonances. We explain the observed spectroscopic features as molecular states emerging in the presence of the light field using a Fano model. For atoms arranged on a lattice, we predict the strong continuum coupling to even stabilize triatomic molecules and find the first signatures of these by observing three-atom loss correlations using quantum gas microscopy. Our results present a mechanism to control decoherence and bind polyatomic molecules using strong light-matter interactions. Published by the American Physical Society 2024
We study long range interactions between two Rydberg atoms and predict the existence of ultralong range Rydberg dimers with equilibrium distances of many thousands of Bohr radii. We calculate the dispersion coefficients C5, C6, and C8 for two rubidium atoms in the same excited level np and find that they scale like n(8), n(11), and n(15), respectively. We show that for certain molecular symmetries these coefficients lead to long range potential wells that can support molecular bound levels. Such macrodimers would be very sensitive to their environment and could probe weak interactions. We suggest experiments to detect these macrodimers.
Chemical Physics In a Rydberg state, an atom has been very nearly, but not quite, ionized. This puts the electron relatively far from the nucleus, and two atoms in such a state can thus form a rather long-range bond. Hollerith et al. observed this phenomenon in fine detail by exciting pairs of ultracold rubidium atoms along the diagonal of an optical lattice. The authors resolved the vibrational state structure spectroscopically and showed that the Rydberg dimers manifested bond lengths exceeding 700 nanometers. Science , this issue p. [664][1] [1]: /lookup/doi/10.1126/science.aaw4150