## Principal Investigator

# Jianshu Cao

jianshu [at] mit.edu

Our group develops theoretical models for understanding the structure and dynamics of complex molecular systems. Establishing relationships between these models and experimental observables allows us to explore new ways of describing chemical and biological processes on multiple time and length scales.

## Postdoctoral Associates

# Aurelia Chenu

achenu [at] mit.edu

My research interests span over a wide range of domains targeting non-equilibrium quantum physics, and include quantum optics, quantum dynamics, quantum statistical mechanics as well as quantum biology. On the one hand, I am interested in the quantum properties of thermal states. While thermal states are fundamental in many areas of physics, their standard quantum description differs drastically from their classical description. I developed new, non-traditional representations of thermal states in terms of quasi-classical wave packets. Such representations can be expected to provide insight into the quantum features of the thermal equilibrium as well as into the quantum-to-classical transition. This formalism is likely to provide a rare bridge between different communities, namely quantum optics, quantum statistical mechanics as well as quantum thermodynamics. On the other hand, I study quantum transport in open systems, such as excitonic energy transport in light-harvesting photosynthetic complexes. For example, through the simulation of third-order response functions, my research provided rationales for the origin of the long-lived oscillations observed in 2D spectra of photosynthetic complexes. More generally, I am interested in developing models from QED and study the approximations yielding the classical regime.

# Chang-Yu Hsieh

changyuh [at] mit.edu

My current research focuses on the following topics: 1) open quantum dynamics of simple systems embedded in a highly Non-Markovian spin bath. This effort helps to understand and design control protocol to suppress decoherence of solid state qubits in the low temperature regime where qubit-phonon interactions can be safely ignored. We also consider the energy transport through a molecular junction (or quantum dot) with spin baths as effective heat sources. 2) Quantum-classical Mapping. Through the framework of Lie algebra and geometry, we attempt to approximate a finite-level quantum system with an effective classical system. Such a mapping allows us to efficiently calculate the nonlinear response properties of a finite-level quantum system (say, electronic degrees of freedom in a molecular system) for an optical experiment.

# Dazhi Xu

dazhixu [at] mit.edu

Recently my interests focus on the quantum thermodynamics, especially the microsystem which is embed in a non-equilibrium or fluctuation dominated environment. For example, via the polaron transform technic, we solved the efficiency of a three-level quantum heat engine which is subject to a strongly coupled non-equilibrium environment. Currently, I am studying the thermodynamics of a quantum open system which is subjected to time-dependent control. I also interested in applying the concepts of small system thermodynamics into the realistic quantum systems, such as cavity-QED, circuit-QED and optomechanics.

## Postgraduates

# Chern Chuang

chernc [at] mit.edu

Recent advances in experimental characterization of natural (chlorosome in green sulfur bacteria) and artificial tubular aggregates had shed light on the optical and dynamical energy transfer properties of these systems. My current work is focusing on the calculation these physical properties based on exciton models. In specific, we apply the theory of multichromophoric Foerster resonance energy transfer to these gigantic light-harvesting systems.

# Evan Piephoff

depiepho [at] mit.edu

Recent advances in condensed-phase spectroscopy have afforded single-molecule analysis, which lends itself to unique insights into dynamic molecular behavior. On the theoretical front, single-molecule kinetic processes can be described by several equivalent stochastic formalisms. Initially developed for renewal processes (those with a single type of monitored transition), the self-consistent pathway framework is one such formalism of particular interest because it can describe generic kinetic schemes in terms of measurable waiting-time distribution functions of arbitrary form (i.e., constituent transitions need not be Poissonian). The focus of my current research is on extending this formalism to non-renewal processes, such as enzymatic turnovers with conformational fluctuations and fluorescence with multiple emission states, and characterizing the information content, including the non-Markovian memory effects, of such signals in terms of measurable parameters.