Rydberg atoms, with their giant electronic orbitals, exhibit dipole-dipole interaction reaching the GHz range at a distance of a micron, making them a prominent contender for realizing ultrafast quantum operations. However, such strong interactions between single atoms have never been harnessed so far because of the stringent requirements on the fluctuation of the atom positions and the necessary excitation strength. Here, we introduce novel techniques to explore this regime . First, we trap and cool atoms to the motional quantum ground-state of holographic optical tweezers allowing to control the inter-atomic distance down to 1.5 µm with a quantum-limited precision of 30 nm. Then, we use ultrashort laser pulses to excite a pair of these close-by atoms to a Rydberg state simultaneously, far beyond the Rydberg blockade regime , and perform Ramsey interferometry with attosecond precision. This allows us to induce and track an ultrafast interaction-driven energy exchange completed on a timescale of nanoseconds, two orders of magnitude faster than in any other Rydberg experiments with individual atoms. This ultrafast coherent dynamic gives rise to a conditional phase which is the key resource for a quantum gate, opening the path for quantum simulation  and computation operating at the speed-limit set by dipole-dipole interactions with this ultrafast Rydberg platform.
 Y. Chew et al., arXiv: 2111.12314
 V. Bharti et al., arXiv : 2201.09590
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