Benchmarking Atomic Ionization Driven by Strong Quantum Light

Abstract

The recently available high-intensity quantum light pulses provide novel tools for controlling light-matter interactions. However, the rigor of the theoretical frameworks currently used to describe the interaction of strong quantum light with atoms and molecules remains unverified. Here, we establish a rigorous benchmark by solving the fully quantized time-dependent Schrödinger equation for an atom exposed to bright squeezed vacuum light. Our \textit{ab initio} simulations reveal a critical limitation of the widely used $Q$-representation: although it accurately reproduces the total photoelectron spectrum after tracing over photon states, it completely fails to capture the electron-photon joint energy spectrum. To overcome this limitation, we develop a general theoretical framework based on the Feynman path integral that properly incorporates the electron-photon quantum entanglement. Our results provide both quantitative benchmarks and fundamental theoretical insights for the emerging field of strong-field quantum optics.

Figures (2)

• Figure 1: (a) Joint photon-photoelectron energy spectrum obtained from the full quantum TDSE simulation. (b) Magnified view of the joint energy spectrum for photon numbers in the range $25000-25010$. The upper panel shows the results from the full quantum TDSE simulation, while the lower panel shows the corresponding results from the $Q$-representation method. (c) Photoelectron energy spectra correlated with specific Fock states. The upper and middle panels show the spectra for $n=25000$ and $n=25001$, respectively, while the lower panel shows their averaged result. Solid and dashed curves denote the results from the full quantum TDSE and the $Q$-representation methods, respectively. (d) Total photoelectron energy spectra calculated using the full quantum TDSE simulation (black solid curve) and the $Q$-representation method (red dashed curve).
• Figure 2: (a) Comparison of the photon-number distributions of $400$ nm BSV light after interaction with a 1D hydrogen atom, calculated using the full quantum TDSE (black solid line), the $Q$-representation (red dashed line), and the path integral method (blue dotted line). The photon-number distribution of the incident BSV light is shown by the gray dash-dotted line. The upper and lower panels show the distributions for even and odd photon-number states, respectively. (b) Magnified photon-number distribution from the full quantum TDSE simulation in the range $12000-12010$. The red dashed line shows the result obtained using the $Q$-representation. (c) Same as (b), but in the range $20000-20010$.