krB

KRb is the diatomic molecule formed from potassium (K) and rubidium (Rb). As a heteronuclear diatomic, KRb in its electronic ground state is a polar molecule with a permanent electric dipole moment, enabling long-range, anisotropic interactions between molecules in ultracold ensembles.

In ultracold-atom experiments, KRb is typically created from mixtures of ultracold K and Rb atoms. A common two-step route uses magnetoassociation across a Feshbach resonance to form weakly bound molecules, followed by coherent optical transfer, such as stimulated Raman adiabatic passage (STIRAP), to the rovibrational ground state. This approach has produced ground-state KRb molecules and enabled studies of dipolar interactions in quantum gases. The first demonstrations involved mixtures including the fermionic 40K and bosonic 87Rb, illustrating control over internal and external degrees of freedom and paving the way for dipolar many-body physics.

Ground-state KRb molecules have a sizable dipole moment, on the order of half a Debye, which can be oriented and tuned with electric fields. This makes KRb a central platform for quantum simulation and quantum information experiments, as well as for exploring ultracold chemical reactions and state-controlled chemistry.

A major experimental challenge is chemical reactivity: two KRb molecules can react to form K2 and Rb2, leading to trap loss. Reaction rates depend on quantum statistics, confinement, and internal state. Ongoing work seeks to extend lifetimes and enable more complex quantum simulations with KRb.