Dipolar spin-exchange and entanglement between molecules in an optical tweezer array

Abstract

Ultracold polar molecules are promising candidate qubits for quantum computing and quantum simulations. Their long-lived molecular rotational states form robust qubits, and the long-range dipolar interaction between molecules provides quantum entanglement. In this work, we demonstrate dipolar spin-exchange interactions between single calcium monofluoride (CaF) molecules trapped in an optical tweezer array. We realized the spin-12 quantum XY model by encoding an effective spin-12 system into the rotational states of the molecules and used it to generate a Bell state through an iSWAP operation. Conditioned on the verified existence of molecules in both tweezers at the end of the measurement, we obtained a Bell state fidelity of 0.89(6). Using interleaved tweezer arrays, we demonstrate single-site molecular addressability. Editor’s summary Ultracold atoms have long been candidates to be the building blocks of quantum information. Even more appealing are cold molecules, which have a richer energy-level structure and offer possibilities that atoms do not. However, achieving entanglement, one of the essential ingredients of a quantum information platform, has been difficult in a molecular system. Now, two groups, Holland et al. and Bao et al., have reached this goal using the dipolar interactions between calcium fluoride molecules placed in optical tweezers (see the Perspective by Smerzi). —Jelena Stajic Dipolar interactions between calcium fluoride molecules are used to create Bell states of molecules.