Simon L.Cornish

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] to demonstrate robust storage qubits in the molecule [3] and will describe the development of magic-wavelength traps [4] that support second-scale rotational coherences giving access to controllable dipolar interactions [5].

I will also report on new experiments that produce single molecules in optical  tweezers starting from a single  Rb and a single Cs atom [6]. Using this platform, we prepare the molecules in the motional ground state of the trap and can perform addressing and detection of single molecules [7]. Using mid-sequence detection of formation errors, we demonstrate rearrangement to produce small defect-free arrays [8]. 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 [9].

Finally, as an outlook, I will describe on-going work to leverage the rich internal structure of molecules by coupling many states together simultaneously with microwave fields to realise synthetic dimensions. As an example, I will report the implementation of the Su-Schrieffer-Heeger (SSH) model using up to 8 rotational levels in the molecule.

D.K. Ruttley and T.R. Hepworth et al., “Long-lived entanglement of molecules in magic-wavelength optical tweezers”, Nature 637, 827 (2025).

P.K. Molony et al., “Creation of Ultracold RbCs Molecules in the Rovibrational Ground State”, Phys. Rev. Lett. 113, 255301 (2014).

P.D. Gregory et al., “ac Stark effect in ultracold polar RbCs molecules”, Phys. Rev. A 96, 021402(R) (2017).

P.D. Gregory et al., “Robust storage qubits in ultracold polar molecules”, Nature Physics 17, 1149-1153 (2021).

Q. Guan et al., “Magic conditions for multiple rotational states of bialkali molecules in optical  lattices”, Phys. Rev. A 103, 043311 (2021).

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).

R.V. Brooks et al., “Preparation of one Rb and one Cs atom in a single optical tweezer”, New J. Phys. 23, 065002 (2021).

D.K. Ruttley, A. Guttridge et al., “Formation of ultracold molecules by merging optical tweezers”, Phys. Rev. Lett. 130, 223401 (2023).

D.K. Ruttley et al., “Enhanced Quantum Control of Individual Molecules Using Optical Tweezer Arrays”, PRX Quantum 5, 020333 (2024).