Can we manipulate a photochemical process of molecules by simply engineering their photonic environment? In this Chem Sci, we demonstrated that this is indeed possible. Explicitly, through exact real-time quantum dynamics, we show that the nonadiabatic dynamics of a pyrazine molecule can change significantly when it strongly couples to the vacuum fluctuations of the electromagnetic field confined inside an optical resonator.

# My paper "Diagrammatic time-local master equation for open quantum systems" is accepted by Phys Rev A.

We all know that an isolated quantum system is governed by the Schodinger equation. However, in real world, a quantum system is always interacting with the surrounding (possibly macroscopic) environment. Such unavoidable interactions are an essential ingredient that contributes to the fact that we are living in a classical world.

Unfortunately, we typically are not able to follow the dynamics for the full system+environment considering the environment may consist of hundreds of degrees of freedom. In many cases, we are only interested in the primary system instead of the environment, we can focus on the reduced density matrix of the system only. The important question is then: How do we describe the evolution of the reduced density matrices?

In this manuscript, I introduce single Feynman diagrams and rules to directly write down the exact time-local master equation for a general open quantum system interacting with an arbitrary environment.

# Launching Project LIME

My dream is to create a simple-to-use and universal package for light-matter interaction covering a wide variety of areas in Theoretical/Computational Chemistry and Physics including nonlinear molecular spectroscopy, polaritonic chemistry, cavity quantum electrodynamics, quantum optics, Floquet engineering, etc.

The name, suggested by my colleague Daniel, stands for LIght-Matter Everything.

The main motivation is Science can be advanced much faster without reinventing the wheel over and over again.

Current modules can be found in GitHub.

Welcome to JOIN!

# Our paper on contrasting quantum decoherence and classical noise model is out!

Our paper on contrasting quantum decoherence and classical noise model is published in J. Chem. Phys. Quantum decoherence can be understood in several pictures. The most rigorous one being the system-bath model. In it, the bath is treated quantum mechanically and decoherence arises due to the system-bath entanglement generated by their interaction. A much simpler picture is the classical noise model whereby the effects of bath is to introduce a time-dependent stochastic term into the system. As such, decoherence appears from a statistical average of the stochastic but unitary dynamics. The intriguing question is whether the simple intuitive classical noise picture can reproduce the decoherence dynamics in a full quantum model. In this paper, we develop general criteria for the classical model to mimic quantum decoherence.

# Our paper on the optical properties of laser-driven matter is out.

Our paper on the optical properties of laser-driven matter is published in Phys. Rev. A. In this work, we develop a theory of optical absorption that is valid for non-equilibrium systems, in particular, laser-driven systems. We applied this theory to investigate the emergent optical absorption properties of a nanoscale semiconductor driven by a intense non-resonant light. It turns out that the optical absorption properties of a laser-driven matter is qualitatively different from the pristine material. Depending on the strength of the dressing light, it can generates replicas of absorption bands that are separated by integer number of photon energies, and generates absorption/emission signals at THz regime.

# Book Recommendation 7 – quantum theory of light

Theoretical chemists think light as semiclassical in the sense that the quantum nature of light is not affecting chemistry. Technically speaking, the light field comes into play in the basic equation to describe chemistry, time-dependent Schodinger equation, as an external time-dependent parameters. However, light is quantum mechanical in nature. And with the advent of nonclassical light realized in labrarotory, it is essential to go beyond the semiclassical view and take a full quantum mechanical treatment of light.

If you are interested in a deep understanding of light, the book “Quantum Optics” by Scully and Zubairy is an excellent book that gives a comprehensive introduction to the quantum mechanical properties of light. The prerequisite, in my opinion, is familiarity with basic quantum mechanics.

# Moving to Irvine, CA

I officially start my postdoc position at the University of California, Irvine working with Prof. Shaul Mukamel. I will work on manipulating and controlling chemistry by optical cavities.