Seminare

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). [mehr]

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. [mehr]

Development of quantum hardware and software is progressing rapidly. With the availability of first generally-accessible quantum computers, their potential use for applications can increasingly be explored. One prospective field of application is data science in the medical sector, which faces challenges difficult to address with currently available methods. An example is medical imaging, where frequently only limited training data is available – making the use of classical AI methods difficult. However, presently available quantum computers are still limited in the number of qubits, the connectivity and are affected by noise. [mehr]

I will review my recent progresses in high harmonic generation in semiconductors, stepping from its classical nature to the recent evidence of its non-classical properties. [mehr]

The pseudogap is mysterious metallic state of electrons which appears above the critical temperature of correlated electron superconductors, most prominently in the lightly-hole-doped cuprates. I argue that the pseudogap is best understood as the finite temperature realization of a metallic ground state with a spin liquid character, andpresent a theory using a bi-layer of ancilla qubits. This theory leads to a variational wavefunction for the pseudogap state, to gauge theories for transitions and crossovers out of the pseudogap, and to a unifying perspective on the cuprate phase diagram. [mehr]