Ultrafast Spectroscopy & Quantum Optics

Research Overview

Our group studies the interaction of light with matter by using cutting-edge optical tools. We are interested in many-body quantum systems consisting of interacting atoms, molecules or electrons. Examples include dense atomic vapors, layered 2D semiconductors and supramolecular structures. We develop and utilize techniques and ideas in ultrafast spectroscopy and quantum optics, such as multidimensional coherent spectroscopy and quantum entanglement, to probe and manipulate quantum dynamics of such systems. The group explores fundamental physics associated with these problems and facilitates unique applications in fields such as quantum information processing, solar energy conversion, optoelectronics, metrology, imaging, sensing and biomedical science.

Optical Multidimensional Coherent Spectroscopy

The concept of Multidimensional Coherent Spectroscopy originated in nuclear magnetic resonance (NMR) and revolutionized NMR studies of the structure and dynamics of bio-molecules. By using state-of-the-art femtosecond lasers, the same concept can be implemented in the optical region. Optical Multidimensional Coherent Spectroscopy has been proved to be a powerful tool for studying couplings and dynamics in complex systems. We use this technique to study many-body interactions and dynamics in atoms/molecules, semiconductor nanostructures and other solid state systems.

Many-body physics in atomic/molecular vapors

Interatomic and intermolecular interactions are among the most fundamental processes in atomic, molecular and optical physics. The nature of many-body interactions in even a dilute atomic vapor is still not completely understood. We are interested in understanding the nature of interactions and collision processes in various media under different conditions to answer open questions including: What is the range of interaction? How many atoms should be accounted for? What is the role of the local field? What happens during the collisions? What is the effect of the non-Markovian behaviors? We are also exploring correlation and collective effects in atomic vapor such as supperradiance, single-photon superradiance, collective N-atom Lamb-shift and other emerging behaviors.

Valley dynamics in atomically thin 2D semiconductors

Atomically thin two-dimensional (2D) crystals such as grapheme posses remarkable physical properties, providing opportunities to study new physics and develop novel applications. A new class of 2D materials is layered transition metal dichalcogenides (TMDs). Monolayer TMDs have direct band gap in the visible region and display strong photoluminescence at the K and -K points in the Brillouin zone. The valley-dependent optical selection rules allow selective carrier excitation in on of the two nonequivalent K valleys and manipulation of valley polarization and coherence. This property can be used for valleytronics, which aims to use valley indices as carrier to process information. We use ultrafast optical pulses to probe and control valley dynamics in layered TMDs.