Precise study of asymptotic physics with subradiant ultracold molecules

Weakly bound molecules have physical properties without atomic analogues, even as the bond length approaches dissociation. For instance, the internal symmetries of homonuclear diatomic

molecules result in the formation of two-body superradiant and subradiant excited states. Whereas superradiance1,2,3 has been demonstrated in a variety of systems, subradiance4,5,6 is more

elusive owing to the inherently weak interaction with the environment. Here we characterize the properties of deeply subradiant molecular states with intrinsic quality factors exceeding 1013

via precise optical spectroscopy with the longest molecule–light coherent interaction times to date. We find that two competing effects limit the lifetimes of the subradiant molecules, with

different asymptotic behaviours. The first is radiative decay via weak magnetic-dipole and electric-quadrupole interactions. We prove that its rate increases quadratically with the bond

length, confirming quantum mechanical predictions. The second is non-radiative decay through weak gyroscopic predissociation, with a rate proportional to the vibrational mode spacing and

sensitive to short-range physics. This work bridges the gap between atomic and molecular metrology based on lattice-clock techniques7, enhancing our understanding of long-range interatomic

interactions.

We gratefully acknowledge NIST award 60NANB13D163 and ARO grant W911NF-09-1-0504 for partial support of this work. M.M. acknowledges NSF IGERT DGE-1069260, and R.M. the Polish Ministry of

Science and Higher Education for grant NN204-215539. R.M. also thanks the Foundation for Polish Science for support within the MISTRZ program.

Present address: Present address: Institute of Physics, University of Kassel, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany.,

Department of Physics, Columbia University, 538 West 120th Street New York, New York 10027-5255, USA,

B. H. McGuyer, M. McDonald, G. Z. Iwata, M. G. Tarallo & T. Zelevinsky

Department of Chemistry, Quantum Chemistry Laboratory, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

B.H.M., M.M., G.Z.I. and T.Z. designed the experiments. B.H.M., M.M., G.Z.I., M.G.T. and T.Z. carried out the measurements and interpreted the data. B.H.M. and M.M. co-led the experimental

efforts. W.S. and R.M. carried out the theoretical calculations and interpreted the data. All authors contributed to the manuscript.

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