Image we create a superposition of states, say a|g> + b|e> with a relative phase between the coefficients (or amplitudes) a and b, at time 0, what will happen afterwards is that the superposition will be destroyed and one is left with a statistical mixture of states. This is the decoherence process originating from the inevitable interaction with the surrounding environment. That is to say, there is no closed system in Nature.

One possible strategy to control the decoherence process that we recently proposed is to vary the relative phase between a and b. Check the paper by Hu, Gu, and Franco for a comprehensive study of how this can be done in the context of electronic decoherence (g, e refer to electronic states) due to electron-nuclear couplings.

Rating: 10/10

The book “Photons and Atoms: Introduction to Quantum Electrodynamics” by Claude Cohen-Tannoudji, Gilbert Grynberg, and Jacques Dupont-Roc is beautiful and excellent, and a must-read for those who are interested in the fundamentals of light-matter interaction. While the focus is on atoms, I found most of the contents apply for molecules and ions as well. The discussion with gauge transformation is particularly clear, both perspectives from the Lagrangian and from the Hamiltonian formalism are presented.

Since it contains all the essential knowledge in the beginning of the book, it is rather self-contained. But a basic knowledge of quantum mechanics (first and second quantization for non-relativistic particles) and quantum optics (photons) are quite useful.

For those who are interested in studying cavity QED, the book “Cavity Quantum Electrodynamics: The Strange Theory of Light in a Box” by Sergio M. Dutra gives an introduction to the quantum theory of light confined in a cavity. It starts with a field quantization of electromagnetic field, discusses its interaction with atoms (i.e., Jaynes-Cummings model) and ends up with a discussion of the dissipation of the cavity mode.

I would recommend this to readers who wants to study light-matter interactions in a box. The prerequisite knowledge is a basic knowledge of quantum optics.

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.

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.

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.

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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.

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. 

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.

Our paper on the relationship between electronic interaction and electronic decoherence is published in J. Chem. Phys. In it, we showed that the electronic interactions do not affect electronic decoherence in the pure-dephasing limit, that is when the electronic transitions between the diabatic states are not significant.