Two studies demonstrate on-demand quantum entanglement in ultracold molecules

The controlled creation of quantum entanglement with molecules has been a long-standing challenge in quantum science. Now, in two new studies, researchers report a method for tailoring the quantum states of individual molecules to achieve quantum entanglement on demand. Their strategy presents a promising new platform for the advancement of quantum technologies such as computation and sensing. Quantum entanglement is one of the key defining features of quantum mechanics. It is central to many quantum applications. Because of their rich internal structure and long-lived rotational states, ultracold molecules have been proposed as promising candidates for qubits in quantum computing and quantum simulations. However, while entanglement has been achieved in various atomic, photonic, and superconducting platforms, controlling and manipulating entanglement between molecules on demand experimentally has been difficult. Now, in two different studies, Yicheng Bao and colleagues and Conner Holland and colleagues report a method to achieve controlled quantum entanglement of calcium fluoride (CaF) molecules. Bao et al. and Holland et al. make use of the long-range dipolar interaction between pairs of laser-cooled CaF molecules trapped in a reconfigurable optical tweezer array and successfully demonstrate the creation of a Bell state – an important class of entangled quantum state characterized by maximal entanglement between two qubits. The Bell state is a foundational concept for many quantum technologies. Both studies show that two CaF molecules located in neighboring optical tweezers and placed close enough to sense their respective long-range electric dipolar interaction led to an interaction between tweezer pairs, which dynamically created a Bell state out of the two previously uncorrelated molecules. “The demonstrated manipulation and characterization of entanglement of individually tailored molecules by Bao et al. and Holland et al. paves the way for developing new versatile platforms for quantum technologies,” writes Augusto Smerzi in a related Perspective.