Ultracold polar molecules are an exciting platform for quantum science and technology. The combination of
rich internal structure of vibration and rotation, controllable long-range dipolar interactions and strong coupling
to applied electric and microwave fields has inspired many applications. These include quantum simulation of
strongly interacting many-body systems, the study of quantum magnetism, quantum metrology and molecular
clocks, quantum computation, precision tests of fundamental physics and the exploration of ultracold chemistry.
Many of these applications require full quantum control of both the internal and motional degrees of freedom of
the molecule at the single particle level.
In Durham, we study ultracold ground-state RbCs molecules formed by associating Rb and Cs atoms using a
combination of magnetoassociation and stimulated Raman adiabatic passage [1]. This talk will report our work
on the development of full quantum control of the molecules. Specifically, I will explain how we have mastered
the ac Stark shift due to the trapping light [2] by the development of magic-wavelength traps [3] that support
second-scale rotational coherences giving access to controllable dipolar interactions [4].
I will explain how we are able to produce single molecules in optical tweezers starting from a single Rb and a
single Cs atom [5]. Using this platform, we prepare the molecules mostly in the motional ground state of the
trap and can perform addressing and detection of single molecules [6]. By transferring the molecules into magic-wavelength tweezers, we can prepare long-lived rotational coherences that support spin-exchange interactions
between molecules, enabling the preparation of maximally entangled Bell states with high fidelity [7].
Finally, as an outlook, I will describe several current research directions, including the extension to optical
lattices [8], the realisation of synthetic dimensions within the molecules and the study of resonant interactions
between molecules and Rydberg atoms.
[1] P.K. Molony et al., “Creation of Ultracold RbCs Molecules in the Rovibrational Ground State”,
Phys. Rev. Lett. 113, 255301 (2014).
[2] P.D. Gregory et al., “ac Stark effect in ultracold polar RbCs molecules”,
Phys. Rev. A 96, 021402(R) (2017).
[3] Q. Guan et al., “Magic conditions for multiple rotational states of bialkali molecules in optical
lattices”, Phys. Rev. A 103, 043311 (2021).
[4] P.D. Gregory et al., “Second-scale rotational coherence and dipolar interactions in a gas of ultracold
polar Molecules”, Nature Physics 20, 415–421 (2024).
[5] R.V. Brooks et al., “Preparation of one Rb and one Cs atom in a single optical tweezer”,
New J. Phys. 23, 065002 (2021).
[6] D.K. Ruttley et al., “Enhanced Quantum Control of Individual Molecules Using Optical Tweezer
Arrays”, PRX Quantum 5, 020333 (2024).
[7] D.K. Ruttley and T.R. Hepworth et al., “Long-lived entanglement of molecules in magic-wavelength
optical tweezers”, Nature 637, 827 (2025).
[8] J.M. Mortlock et al., “Multi-state detection and spatial addressing in a microscope for ultracold
molecules”, Nat. Commun. 17, 518 (2026).