Quantum matter based on ultracold molecules

Carl J. Williams, Paul S. Julienne

Kang-Kuen Ni

M. L. Wall, K. R. A. Hazzard, A. M. Rey

This article gives an introduction to the realization of effective quantum magnetism with ultracold molecules in an optical lattice, reviews experimental and theoretical progress, and highlights future opportunities opened up by ongoing experiments. Ultracold molecules offer capabilities that are otherwise difficult or impossible to achieve in other effective spin systems, such as long-ranged spin-spin interactions with controllable degrees of spatial and spin anisotropy and favorable energy scales. Realizing quantum magnetism with ultracold molecules provides access to rich many-body behaviors, including many exotic phases of matter and interesting excitations and dynamics. Far-from-equilibrium dynamics plays a key role in our exposition, just as it did in recent ultracold molecule experiments realizing effective quantum magnetism. In particular, we show that dynamical probes allow the observation of correlated many-body spin physics, even in polar molecule gases that are not quantum degenerate. After describing how quantum magnetism arises in ultracold molecules and discussing recent observations of quantum magnetism with polar molecules, we survey prospects for the future, ranging from immediate goals to long-term visions.

Gael Reinaudi, K. Bega, Tanya Zelevinsky

Igor B. Mekhov

An optical nondestructive method for in situ detection of the bound states of ultracold polar molecules is developed. It promises a minimally destructive measurement scheme up to a physically exciting quantum non-demolition (QND) level. The detection of molecular complexes beyond simple pairs of quantum particles (dimers, known, e.g., from the BEC–BCS theory) is suggested, including three-body (trimer) and four-body (tertramer) complexes trapped by one-dimensional tubes. The intensity of the scattered light is sensitive to the molecule number fluctuations beyond the mean-density approximation. Such fluctuations are very different for different complexes, which leads to radically different light scattering. This type of research extends ‘quantum optics of quantum gases’ to the field of ultracold molecules. Merging the quantum optical and ultracold gas problems will advance experimental efforts towards the study of the light–matter interaction at its ultimate quantum level, where the quantizations of both light and matter are equally important.

Mara Meyer zum Alten Borgloh, Jule Heier, Fritz von Gierke +4 more

Ultracold molecules provide opportunities for exploring quantum matter, chemical dynamics and information processing thanks to their rich interactions, which can be controlled by external fields. Magnetic fields tune interactions through Feshbach resonances, enabling the formation of ultracold dimers and triatomic molecules from atom-dimer collisions. Here we demonstrate electric-field control of atom-molecule Feshbach resonances. In mixtures of ground-state sodium-potassium molecules and potassium atoms, electric fields shift resonance positions systematically, revealing specific trimer bound states and their electric-field dependent energies. The response differs markedly from isolated dimers, showing hindered rotation of the molecular constituent near an atom. Electric fields therefore add an independent knob for atom-molecule resonances, open spectroscopic access to triatomic quantum states, and advance controlled polyatomic quantum matter.