Durham University Team Advances Quantum Science with Control of Individual Molecules

Researchers from Durham University and the Joint Quantum Centre DurhamNewcastle have developed a set of techniques for controlling and reading the quantum states of individual molecules. The team used arrays of up to eight Rb and eight Cs atoms to assemble arrays of RbCs molecules, demonstrating global microwave control of multiple rotational states. They also implemented site-resolved addressing and state control using an auxiliary tweezer array. The ability to control and readout individual molecules in a single internal and external quantum state could have significant implications for quantum simulation, quantum information processing, ultracold chemistry, and precision measurement.

What is the Significance of Quantum Control of Individual Molecules?

The control over the quantum states of individual molecules is a crucial aspect in the quest to harness their rich internal structure and dipolar interactions for applications in quantum science. This paper, authored by Daniel K Ruttley, Alexander Guttridge, Tom R Hepworth, and Simon L Cornish from the Department of Physics at Durham University and the Joint Quantum Centre DurhamNewcastle, develops a toolbox of techniques for the control and readout of individually trapped polar molecules in an array of optical tweezers.

The researchers started with arrays of up to eight Rb and eight Cs atoms, assembling arrays of RbCs molecules in their rovibrational and hyperfine ground state with an overall efficiency of 48.2%. They demonstrated global microwave control of multiple rotational states of the molecules and used an auxiliary tweezer array to implement site-resolved addressing and state control.

The rotational state of the molecule can be mapped onto the position of Rb atoms, and this capability was used to readout multiple rotational states in a single experimental run. Furthermore, using a scheme for the mid-sequence detection of molecule formation errors, the researchers performed rearrangement of assembled molecules to prepare small defect-free arrays. They also discussed a feasible route to scaling to larger arrays of molecules.

How Does Ultracold Molecules Contribute to Quantum Science?

Ultracold molecules offer a versatile platform for quantum science, with applications spanning quantum simulation and quantum information processing to ultracold chemistry and precision measurement. Molecules feature a rich internal structure constituting a ladder of rotational states with long radiative lifetimes. Preparing molecules in a superposition of rotational states engineers dipole-dipole interactions that can be controlled using microwave fields.

These properties make rotational states well suited for applications as qubits or pseudospins in a quantum simulator. Moreover, the abundance of long-lived rotational states unlocks possibilities such as synthetic dimensions in the rotational degree of freedom, realization of qudits, or the implementation of quantum error-correcting codes in the molecules’ internal states.

Realization of many of these theoretical proposals demands a high level of control of the quantum states of individual molecules. Attaining such control is pivotal to exploit the wide array of tools offered by ultracold molecules for quantum science. Significant progress has been made in preparing and manipulating internal and external states of molecules, but control and detection of individual molecules in a single internal and external quantum state is an ongoing challenge.

What Role Do Optical Tweezer Arrays Play in Quantum Science?

Optical tweezer arrays are a powerful platform for the trapping, control, and readout of single ultracold particles. Arrays of tweezers are dynamically reconfigurable, allowing flexible connectivity and enabling the preparation of states with low configurational entropy through rearrangement of particles. In this tweezer array platform, long-range interactions between trapped particles have been utilized to simulate complex quantum systems.

The platform’s inherent scalability provides a promising avenue for constructing arrays with an even greater number of particles. The extension of tweezer arrays to ultracold molecules has been realized recently for both laser-cooled and assembled molecules. For neutral atom tweezer arrays, a range of experimental techniques have been demonstrated, including rearrangement, erasure conversion, and mid-circuit operations.

In this work, the researchers developed a similar toolbox of techniques for the control and readout of ultracold bialkali molecules trapped in arrays of optical tweezers. Specifically, they globally and locally controlled multiple rotational states of individually trapped ultracold molecules.

How Can Multiple Rotational States Be Detected in a Single Experiment?

The researchers introduced a technique for the readout of multiple rotational states in a single iteration of the experiment, achieved by mapping onto atomic states and demonstrating rearrangement of molecules using mid-sequence detection of formation errors.

The structure of the paper includes an overview of the experimental platform, a description of the procedure for the assembly of molecules in optical tweezers, and reports the efficiency of this process. It also demonstrates global control of the rotational states of molecules in the optical tweezer array using microwave fields to perform coherent multiphoton excitation.

The paper describes the detection of multiple rotational states of molecules in a single experimental run, demonstrates local control of rotational states using an addressing tweezer in combination with microwave fields to selectively excite specific molecules in the array, and describes the detection of molecule formation errors and rearrangement of molecules to prepare a defect-free array.

What is the Future of Scaling Techniques in Quantum Science?

The researchers examined the prospects for scaling the techniques described in this paper to larger arrays. The experimental apparatus used to produce ultracold RbCs molecules trapped in one-dimensional arrays of optical tweezers was a key aspect of the experimental setup.

The use of two distinct wavelengths of optical tweezers enabled species-specific trapping and independent control of the atoms and molecules. Tweezers at a wavelength of 1066 nm were attractive to all species.

The research conducted by the team at Durham University and the Joint Quantum Centre DurhamNewcastle is a significant step forward in the field of quantum science. The ability to control and readout individual molecules in a single internal and external quantum state opens up new possibilities for quantum simulation, quantum information processing, ultracold chemistry, and precision measurement.