Geoffrey Iwata

Precise study of asymptotic physics with subradiant ultracold molecules

An experimental study characterizes subradiance—inhibited emission due to destructive interference—in ultracold molecules close to the dissociation limit and shows that it could be used for precision molecular spectroscopy. 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.

Thermometry via Light Shifts in Optical Lattices

For atoms or molecules in optical lattices, conventional thermometry methods are often unsuitable due to low particle numbers or a lack of cycling transitions. However, a differential spectroscopic light shift can map temperature onto the line shape with a low sensitivity to trap anharmonicity. We study narrow molecular transitions to demonstrate precise frequency-based lattice thermometry, as well as carrier cooling. This approach should be applicable down to nanokelvin temperatures. We also discuss how the thermal light shift can affect the accuracy of optical lattice clocks.

Control of Optical Transitions with Magnetic Fields in Weakly Bound Molecules.

In weakly bound diatomic molecules, energy levels are closely spaced and thus more susceptible to mixing by magnetic fields than in the constituent atoms. We use this effect to control the strengths of forbidden optical transitions in (88)Sr2 over 5 orders of magnitude with modest fields by taking advantage of the intercombination-line threshold. The physics behind this remarkable tunability is accurately explained with both a simple model and quantum chemistry calculations, and suggests new possibilities for molecular clocks. We show how mixed quantization in an optical lattice can simplify molecular spectroscopy. Furthermore, our observation of formerly inaccessible f-parity excited states offers an avenue for improving theoretical models of divalent-atom dimers.

High-precision spectroscopy of ultracold molecules in an optical lattice

The study of ultracold molecules tightly trapped in an optical lattice can expand the frontier of precision measurement and spectroscopy, and provide a deeper insight into molecular and fundamental physics. Here we create, probe, and image microkelvin

BaH molecular spectroscopy with relevance to laser cooling

^{88}

High-resolution optical spectroscopy with a buffer-gas-cooled beam of BaH molecules

Sr

Towards laser cooling and trapping of barium monohydride

_2

A buffer gas cooled beam of barium monohydride

molecules in a lattice, and demonstrate precise measurements of molecular parameters as well as coherent control of molecular quantum states using optical fields. We discuss the sensitivity of the system to dimensional effects, a new bound-to-continuum spectroscopy technique for highly accurate binding energy measurements, and prospects for new physics with this rich experimental system.