Long-lived entanglement of molecules

Achieving precise quantum control of particles is key to advancing quantum technology and deepening our understanding of fundamental science. In the strange world of quantum mechanics, particles can behave in ways that defy our everyday intuition. For instance, they can exist in "superpositions," where they effectively occupy two states at once, or become "entangled," forming a connection that allows them to influence each other even when far apart. These phenomena, if controlled, could lead to huge advances in computation and understanding the nature of complex materials.
Foundational work in quantum science has been performed using systems like trapped atoms and superconducting circuits. Expanding this level of control to more complex systems, such as molecules, could lead to exciting possibilities. For example, it could allow us to study fundamental physics in greater detail or develop compact memories for quantum computers. However, the very complexity that makes these systems so appealing also makes them highly sensitive to their surroundings. This sensitivity can disrupt their fragile quantum states, leading to the loss of any information stored within them.
We set out to solve this challenge by trapping individual molecules in tightly focused laser beams. By using a carefully selected colour of laser light, we isolate the molecules' internal states from their surroundings. In this setup, we achieved long coherence times between the molecules' rotational states. By bringing two molecules close together, we detected tiny interactions between them and used these to create long-lived quantum entanglement. Looking ahead, we expect our work to open the door to using molecules as dense quantum memories and for highly precise measurements in quantum-enhanced technologies.

An illustration of two entangled molecules which are individually trapped in tightly focussed laser beams.
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