Dynamic transients are a natural ingredient of out-of-equilibrium quantum systems. One paradigmatic example is Dicke superradiance, describing the collectively enhanced population inversion of an ensemble of two-level atoms coupled to a single mode of the electromagnetic field.
Here, we present a new approach exploiting superradiance to engineer dynamical tunneling in a synthetic lattice geometry. Our experimental implementation is based on a spinor Bose-Einstein condensate (BEC), which is coupled to a single mode of an ultrahigh-finesse optical cavity . Transverse laser fields induce cavity-assisted Raman transitions between discrete momentum modes of two spin levels, which we interpret as photon-assisted tunnelling in a momentum-space lattice. In particular, the tunnelling rate evolves dynamically with the emergent cavity field. By monitoring the cavity leakage, we gain real-time access to the lattice currents and benchmark their collective behaviour .
In a series of recent experiments, we engineer an atomic mode parametric amplifier induced by virtual cavity photons. The spinor BEC is initialized in the |F = 1, mF = 0⟩ Zeeman sublevel (pump mode), and correlated pairs of atoms in |mF = ±1⟩ (signal and idler modes) are created by four-photon processes, which involve scattering of virtual cavity photons in a far-detuned regime. The pair production is highly non-linear, as evidenced by its scaling with atom number. Moreover, the spin pairs are ejected out of the BEC with opposite relative momenta, in resemblance parametric four-wave mixing. While similar to collisional spin-mixing dynamics , the timescales of this process (~10 μs) are significantly faster, providing prospects rapid entanglement production in cold atom experiments.
 F. Ferri, R. Rosa-Medina, F. Finger, N. Dogra, M. Soriente, O. Zilberberg, T. Donner, T. Esslinger,
(2021). Emerging dissipative phases in a superradiant quantum gas with tunable decay. Physical Review X, 11(4), 041046.
 R. Rosa-Medina, F. Ferri, F. Finger, N. Dogra, K. Kroeger, R. Lin, R. Chitra, T. Donner,
T. Esslinger, (2022). Observing dynamical currents in a non-Hermitian momentum lattice. Physical Review Letters, 128(14), 143602.
 L. Pezze, A. Smerzi, M.K. Oberthaler, R. Schmied, P.Treutlein, (2018). Quantum metrology with nonclassical states of atomic ensembles. Reviews of Modern Physics, 90(3), 035005.
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|Presenter name||Rodrigo Rosa-Medina|