# Local optical control of the resonant dipole-dipole interaction between Rydberg atoms

## TL;DR

This paper demonstrates local optical control over Rydberg atom interactions, enabling tuning of spin states, observation of superradiant and subradiant states, and dynamic freezing, advancing quantum simulation capabilities.

## Contribution

It introduces a method for local optical tuning of Rydberg atom interactions, allowing control over spin dynamics and state preparation for quantum simulation.

## Key findings

- Observation of bright and dark states in two-spin systems.
- Control of spin exchange dynamics with laser-induced shifts.
- Preservation of coherence during interaction freezing.

## Abstract

We report on the local control of the transition frequency of a spin-$1/2$ encoded in two Rydberg levels of an individual atom by applying a state-selective light shift using an addressing beam. With this tool, we first study the spectrum of an elementary system of two spins, tuning it from a non-resonant to a resonant regime, where "bright" (superradiant) and "dark" (subradiant) states emerge. We observe the collective enhancement of the microwave coupling to the bright state. We then show that after preparing an initial single spin excitation and letting it hop due to the spin-exchange interaction, we can freeze the dynamics at will with the addressing laser, while preserving the coherence of the system. In the context of quantum simulation, this scheme opens exciting prospects for engineering inhomogeneous XY spin Hamiltonians or preparing spin-imbalanced initial states.