Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 23: Ultra-fast phenomena
HL 23.9: Talk
Tuesday, March 17, 2020, 12:00–12:15, POT 112
Non-perturbative subcycle nonlinearities of ultrastrong light-matter coupling — •Joshua Mornhinweg1, Maike Halbhuber1, Cristiano Ciuti2, Dominique Bougeard1, Rupert Huber1, and Christoph Lange1 — 1University of Regensburg, Germany — 2Université de Paris, France
In the ultrastrong-coupling regime, the rate of energy exchange between the light field of an optical resonator and an electronic excitation - the vacuum Rabi frequency, ΩR - is comparable to the carrier frequency of light, ωc, and anti-resonant interaction terms govern the dynamics. In this setting, novel quantum effects including the vacuum Bloch-Siegert shift, modified electronic transport, or light-induced superconductivity have been explored. Yet, little is known about the nonlinearities of this extreme regime of light-matter interaction. Here, we investigate extreme subcycle nonlinearities of Landau cavity polaritons with a coupling strength of ΩR/ωc=0.6. Two-dimensional terahertz (THz) spectroscopy probes the response with amplitude and phase resolution, on a subcycle scale. In a strong-field setting of multiple THz photons per Landau electron, the dynamics include pump-probe as well as four and six-wave mixing processing observed for each of the polaritons. Most importantly, we observe off-diagonal contributions, which our Liouville path analysis links to nonlinear interactions between the individual polariton states and to a collapse of the normal-mode approximation. Our quantitative microscopic theory links the nonlinearities to coherent Coulomb correlations resulting from non-perturbative excitation of the Landau system.