Shaping the Hamiltonian Ultracold atoms have proven to be a versatile setting for simulating more complicated quantum systems. However, the type of the simulated Hamiltonian usually cannot be changed once the system has been engineered, although the parameters can be tuned. Geier et al . used rubidium-87 atoms in two excited Rydberg states to create a system in which the type of the Hamiltonian could be modified by periodic driving. The researchers started with a system that was initially described by the so-called Heisenberg XX Hamiltonian. By using a periodic series of pulses, the Hamiltonian was transformed into a different target Hamiltonian, which was corroborated by monitoring the system’s dynamics. —JS

We predict a resonant enhancement of the nonlinear optical response of an interacting Rydberg gas under conditions of electromagnetically induced transparency. The enhancement originates from a two-photon process which resonantly couples electronic states of a pair of atoms dressed by a strong control field. We calculate the optical response for the three-level system by explicitly including the dynamics of the intermediate state. We find an analytical expression for the third order susceptibility for a weak classical probe field. The nonlinear absorption displays the strongest resonant behavior on two-photon resonance where the detuning of the probe field equals the Rabi frequency of the control field. The nonlinear dispersion of the medium exhibits various spatial shapes depending on the interaction strength. Based on the developed model, we propose a realistic experimental scenario to observe the resonance by performing transmission measurements. arXiv:1909.06802v1 [physics.atom-ph]

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