Molecules arranged like eggs in a carton: a new route to large, ordered arrays for quantum technology
Research news item
Researchers demonstrate deterministic loading of individual molecules into optical tweezers, paving the way toward large, low-entropy arrays for quantum information processing. Molecules could provide powerful building blocks for quantum technologies, but arranging thousands of them into precisely controlled arrays is a major challenge.
Researchers from Radboud University, Columbia University (USA), and the University of Chicago (USA) demonstrate a new way to load individual molecules into arrays of optical tweezers. Their results, recently published in Physical Review Letters, show how microwave-shielded molecular gases can be used to prepare highly ordered arrays of molecules – an important step toward scalable molecular quantum information processing.
Ultracold molecules are promising systems for quantum information processing. Their rotational and nuclear-spin states can serve as exceptionally coherent quantum bits, or qubits. Molecules also interact with one another through their dipole moments, providing a way to implement quantum operations.
To control individual molecules, researchers use optical tweezers: tiny traps made from focused laser light that can hold a single molecule. For useful quantum information processing, however, thousands of these traps need to be filled. This is difficult because optical tweezers are typically loaded with a single molecule only about half of the time. Empty traps make it harder to build large, well-ordered arrays.
Using microwaves as a shield
The researchers address this challenge using microwave shielding. In experiments, microwaves create repulsive interactions between molecules, protecting them from collisions with one another. This allows the molecules to be cooled to extremely low temperatures – in the nano-Kelvin range - and provides a very cold molecular gas from which the optical tweezers can be loaded. For highly polar molecules (such as the sodium-cesium molecules) used in experiments, the microwave-induced repulsive “shield” can extend hundreds of nanometers to around a micrometer. Crucially, this can be larger than the size of an optical tweezer.
Figure: Tweezer traps (red) are loaded with single molecules due to the repulsive shields (blue) created using microwaves (horn). This results in deterministic loading with exactly one molecule per trap. Thermal contact with excess molecules in the surrounding gas cool trapped molecules to the motional ground state, resulting in a low-entropy array.
Like eggs in a carton
The result is similar to putting eggs into a carton: the available space is arranged so that only one egg can fit in each compartment. In the same way, the molecular shield prevents two molecules from occupying the same optical tweezer. Once a molecule is loaded into a trap, another molecule cannot join it. This makes the loading deterministic; each tweezer can be filled with exactly one molecule rather than having only a 50% chance of being occupied.
The surrounding ultra-cold molecular gas can then provide thermal contact that cools the trapped molecules toward the motional ground state of their traps. The result is a highly ordered, low-entropy array of molecules, potentially containing thousands of individually trapped molecules and ready for quantum information processing.
Looking ahead
The work demonstrates a new approach to preparing large arrays of molecules with both controlled occupancy and low motional energy. Such ordered molecular arrays could provide a foundation for scaling up experiments with molecules as quantum bits.
Literature reference
Low-Entropy Arrays of Microwave-Shielded Molecules Prepared by Interaction Blockade Tijs Karman, Sebastian Will, Zoe Z. Yan Physical Review Letters (2026) http://doi.org/10.1103/vprz-jqz5
Contact information
For further information, please contact the researcher involved or team Science communication via +31 24 361 6000 or media [at] ru.nl (media[at]ru[dot]nl).
