Collective Atom Interaction with Photons

Small, cold objects behave in ways that are incredibly bizarre compared to larger, familiar objects of our normal experience. This strange behavior can become more emphatic when many objects interact with each other. Recent advances in our control of small objects have led to prospects of quantum computers and quantum simulators, which could lead to astounding advances in our computational abilities.

Studies of this type in Europe, Asia, and the Americas are leading to rapid advances in the complexity of systems under our control. This project will use theoretical and computational methods to study the interaction between many atoms using light, which has been proposed as a platform for quantum computation and quantum simulation. In particular, this group will focus on cases where the atoms are position into a regular array.

There are many groups around the world that have demonstrated the ability to hold the atoms, for example, on the corners of a repeating square and this group will investigate realistic situations to predict and understand their collective evolution. These systems are hard to understand because changes to one atom affect those on a second atom, which affect those on a third atom …, but their study is eminently worthwhile because it leads to a richness in outcome which is intrinsically interesting and might also serve as the basis of quantum sensors, computers, or simulators.

A key feature of these studies will be the development of theoretical and computational techniques to include all aspects of light-atom interactions, including the recoil of atoms, the polarization of the photon, and many-body coherences.

The focus of this project is the collective interaction of atoms with light where the presence of many atoms changes how they individually interact with the photons. The group will mainly treat atom arrays where the lattice spacing is smaller than the wavelength. For this condition, the retarded dipole-dipole interaction between atoms leads to collective photon-atom interaction: the interaction is qualitatively different from that of a photon with a single atom.

In one group of projects, the group will explore the effect where single photons interacting with an array of atoms leads to momentum and energy transferred to the atoms' center-of-mass motion. This will be investigated at two levels: the approximation where a sudden interaction is assumed and a more accurate treatment including the center of mass quantized motion.

The group will investigate several cases, including how specific collective states lead to kicks for particular atoms in the array and how array pairs could be used to entangle distant qubits and to study fundamental optomechanical studies. The cavity configuration could lead to especially large center-of-mass recoil, which would affect their applications and could lead to interesting fundamental physics as well.

The other group of projects will study how several photons interact with the atom array. New phenomena are expected because when one photon is incident on the array, any atom in the array can be excited, but, with more photons, already excited atoms cannot absorb a second photon. This constraint leads to different correlations and entanglement in the atom array compared to the one photon cases.

One possibility for entanglement is in the spatial wave function of the different atoms because the photon recoil will depend on the presence of excitations of atoms in the array. The group will also study correlation in the photons; correlation can occur when photons are emitted through correlated spontaneous decay during superradiance or could occur when the array transmits photons in pairs or more.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.