Interactions between atoms and light rule the behavior of our physical world, but at the same time, can be extremely complex. Understanding and harnessing them is one of the major challenges for the development of quantum technologies.
To understand light-mediated interactions between atoms, it is common to isolate only two atomic levels, a ground level and an excited level, and view the atoms as tiny antennas with two poles that talk to each other. So, when an atom in a crystal lattice array is prepared in the excited state, it relaxes back to the ground state after some time by emitting a photon.
The emitted photon does not necessarily escape from the array, but instead, it can become absorbed by another ground-state atom, which then gets excited. Such an exchange of excitations, also referred to as dipole-dipole interaction, is key for making atoms interact, even when they cannot bump into each other.
"While the underlying idea is very simple, as many photons are exchanged between many atoms, the state of the system can become correlated, or highly entangled, quickly," explains JILA and NIST Fellow and University of Colorado Boulder physics professor Ana Maria Rey.
"I cannot think of a single atom as an independent object. Instead, I need to keep track of how its state depends on the state of many other atoms in the array. This is intractable with current computational methods. In the absence of an external drive, the generated entanglement typically disappears since all atoms relax to the ground state."
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