Speaker
Description
We propose a framework for employing two-dimensional (2D) spectroscopy to investigate the quantum sine-Gordon (QSG) model. Traditionally used to study the structure and dynamics of molecular systems, 2D spectroscopy is increasingly recognized as a powerful tool for exploring collective excitations in quantum many-body physics. By evaluating 2D maps within a Gaussian ansatz, we quantify the QSG system's response to consecutive (time-delayed) perturbations. This approach enables the identification of key features such as the emergence of quantum breather modes, their bound states, signatures of the theory's non-Gaussian nature, and the effects of disorder. Notably, these results are unattainable by means of the traditional linear response paradigm, since the consecutive perturbations bring the system to states with multiple excitations and thus reveal processes such as breather-breather interactions.
The computed maps provide detailed insights on the out-of-equilibrium dynamics of the QSG model, which can be experimentally investigated through platforms like ultracold atoms and superconducting qubits. As an example, we examine the implications of our spectroscopic protocol in a system of two one-dimensional tunnel-coupled superfluids within a double-well potential: a natural realization of the QSG model. Furthermore, our framework is generalizable to the study of collective excitations in other paradigmatic quantum many-body systems.
Reference: D. De Santis, A. Gómez Salvador, N. Bazhan, S. Erne, M. Prüfer, C. Guarcello, D. Valenti, J. Schmiedmayer, E. Demler, “Momentum-resolved two-dimensional spectroscopy as a probe of nonlinear quantum field dynamics”, arXiv:2509.25147 (2025)