Ab-initio Quantum Electrodynamics – a Theoretical Playground for New Quantum Information Devices

Norah M. Hoffmann¹ ²¹ Simons Centre for Computational Physical Chemistry, Department of Chemistry, New York University, New York, NY 10003, USA² Department of Physics, New York University, New York, NY 10003, USA Corresponding author: [email protected] Abstract: For quantum computing, quantum optical effects such as bound states, spontaneous emission, and superradiance are crucial. However, these effects are typically observed under extreme conditions, such as ultracold temperatures, which limit their scalability. There is a growing effort to reproduce these effects under milder conditions, closer to room temperature, with the aim of achieving scalable quantum information devices. To address the limitations posed by these extreme conditions, novel theoretical and experimental approaches are required. In this talk, I will introduce a new theoretical framework called ab-initio quantum electrodynamics, its computational challenges, and potential solutions, focusing on mixed quantum-classical methods for photons. I will present a Wigner sampling scheme for photons, traditionally applied to electron-nuclear problems, to simulate large-scale light-matter interactions. By accurately accounting for vacuum field statistics and employing mixed quantum-classical trajectories for the evolution, I will demonstrate how this cavity Multi-Trajectory Ehrenfest method (cMTE) provides an efficient means to describe quantum effects such as spontaneous emission and correlation. Additionally, by integrating this approach with real-time Time-Dependent Density Functional Theory, we can scale this method to realistic light-matter systems and investigate these ubiquitous quantum optical effects in real molecules under ambient conditions. Keywords: Quantum information, Ehrenfest dynamics, Wigner sampling, Mixed quantum-classical methods, Spontaneous emission, Quantum electrodynamics, Polaritonics Suggested Reading: Wigner, Eugene. "On the quantum correction for thermodynamic equilibrium." Physical review 40.5 (1932): 749. Hoffmann, Norah M., et al. "Capturing vacuum fluctuations and photon correlations in cavity quantum electrodynamics with multitrajectory Ehrenfest dynamics." Physical Review A 99.6 (2019): 063819. Hoffmann, Norah M., et al. "Benchmarking semiclassical and perturbative methods for real-time simulations of cavity-bound emission and interference." The Journal of Chemical Physics 151.24 (2019). Scully, Marlan O., and M. Suhail Zubairy. Quantum optics. Cambridge university press, 1997. Ullrich, Carsten A. "Time-dependent density-functional theory: concepts and applications." (2011).