Seminars

Abstract. We discuss the question of how can one treat the laser-induced (or laser-assisted)high-order processes of electrons (bound or free) nonperturbatively, in such a way that boththe electron-atom interaction and the quantized nature of radiation be simultaneously takeninto account? An analytic method is proposed to answer this question in the generalframework of nonrelativistic quantum electrodynamics. As an application, a quantum opticalgeneralization of the strong-field Kramers-Heisenberg formula has been derived fordescribing high-harmonic generation (HHG). [more]

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Vibrational spectroscopies - and especially infrared spectroscopy - play an increasingly importantrole in modern biodiagnostics, environmental analysis, and food safety/quality scenarios. This hasled to the evolution of mid-infrared photonics from an emerging tool into an enabling technology.With applications ranging from non-invasive exhaled breath analysis to in-vivo assessment ofcartilage damage, mid-infrared (MIR; 3-20 μm) photonics ranges among the most flexible molecularsensing platforms nowadays available. In particular, with the emergence of quantum and interbandcascade laser technology, the on-chip hybridization and/or integration of entire MIR sensingdevices is on the horizon ultimately leading to IR-lab-on-chip systems. [more]

Precision measurements of the Rydberg spectra of H, He and H₂ will be presented, which aim at determining their ionization energies and, in the case of H₂, also the spin-rovibrational energy-level structure of H₂⁺. These measurements are carried out for comparison with the results of first-principles calculations that include the treatment of finite-nuclear-size effects and relativistic and quantum-electrodynamics corrections up to high order in the fine-structure constant. [more]

The field of quantum computation heavily relies on the belief that quantum computation violates the extended Church Turing thesis, namely, that quantum many-body systems cannot be simulated by classical ones with only polynomial overhead. Importantly, we must ask: what experimental evidence do we have for this bold assumption? A major effort towards providing such evidence had concentrated on random quantum circuit sampling (RCS) as in the famous supremacy experiment by Google from 2019. I will describe a recent work with Gao, Landau, Liu and Vazirani in which we give a polynomial time classical algorithm for simulating such RCS experiments. Our algorithm gives strong evidence that RCS cannot be the basis for near term experimental evidence for scalable exponential quantum advantage. [more]