An efficient framework for quantum dynamics driven by nonclassical light

TL;DR

This paper introduces an efficient framework using a pulse-shaped P-representation to analyze quantum system dynamics driven by nonclassical light, enabling scalable and analytical solutions for complex states.

Contribution

The authors develop a scalable, quasi-classical decomposition method that simplifies the analysis of quantum dynamics under nonclassical light with large photon numbers.

Findings

Exact analytical solutions for two-level systems with exponential pulses.

Method accurately reproduces known results for one- and two-photon states.

Scales efficiently to complex states like Fock, thermal, and squeezed vacuum with large photon numbers.

Abstract

Understanding quantum system dynamics driven by nonclassical light pulses is challenging, particularly for general light states with large photon numbers. Here we introduce an efficient framework that makes this task tractable. By introducing a pulse-shaped P-representation, the exact quantum evolution is decomposed into a mixture of many independent quasi-classical branches, each governed by a standard master equation with a classical pulse which can be solved efficiently. As an illustration, for a two-level system interacting with an exponential pulse, we first find out the exact analytical solutions to the Bloch equations in each quasi-classical branch, and then by taking proper P-function average over all branches, the full system dynamics driven by nonclassical light pulses is analytically obtained. For the one-photon and two-photon cases, our method well reproduces the previous exact results either analytically or numerically. Crucially, our approach scales efficiently to more complex light states (Fock, thermal, squeezed vacuum states) with large photon numbers ($N\sim 100$). We further provide a clear physical interpretation how the system dynamics is influenced through the high-order optical coherence of the nonclassical pulses. This work provides a unified and computationally efficient route and a useful starting point to explore more complex quantum dynamics driven by nonclassical light in quantum optics and quantum information processing.