"The aim of the Extryg project was to address fundamental scientific questions concerning mechanisms of energy transfer between molecules that rely on so-cllaed dipole-dipole interactions. It has long been known that molecules can exchange lumps or quanta of energy if they are sufficiently close. Each molecule acts like a tiny antenna or dipole, exchanging information with others nearby. The open question is to what extent quantum effects like superposition (""being in two places at once"") and entanglement play a role in these processes. There is some evidence that key biological processes such as photosynthesis might exploit these quantum properties to improve their efficiency. A related question is how we might replicate this behaviour in engineered systems.
To study this we proposed to create a model system in the laboratory consisting of chains of laser-cooled rubidium and strontium atoms. By putting the atoms in high-lying energy states known as Rydberg states, their dipole-dipole interactions can be blown up many orders of magnitude in both space and time. The aim was to deterministically place a single excitation in the chain and observe how it was transferred to its neighbours.
During the project we put in place all the key aspects of the model system, and observed the long-range interactions between the atoms. Several new and highly profitable research directions emerged at an early stage. The main conclusions were:
-using rubidium atoms, we showed that optical photons can be coupled in novel ways to the microwave excitation that propagate in the chain. As well as new readout methods for quantum effects, this provides a resource for microwave detection at the quantum level, and for the microwave control of quantum light.
-for Sr atoms, a new direction emerged whereby rather than exciting atoms to the Rydberg state, a laser is instead used to ""mix in"" the properties of the Rydberg state to lower-lying states that are long-lived. We showed that in this way Rydberg properties can be combined with laser cooling to millionths of a degree above absolute zero, opening a route to new types of transport experiment.
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