Multidisciplinary Research Meeting

Doing research independently, thinking outside the box, and becoming an original thinker are key traits of good scientists. However, due to the complexity and rapid growth in modern science, efficient communication, idea exchanges, and collaborations become ever more important. To improve the interaction between our group and other groups at Princeton, Liang (Liang-Yan Hsu) and I will organize a multidisciplinary research meeting program with the aim that our group members exchange ideas with a select constructive broad audience at Princeton, as well as learn new science from each other.

This meeting program is briefly summarized as follows:

(1) Purpose and Goal: The purpose of this meeting program is to improve the interaction between our group and other groups at Princeton. The aim is for young scientists at Princeton to exchange ideas and collaborate with each other.

(2) Topics and Speakers: In this program, Liang will organize this meeting program and invite speakers from the Princeton center for theoretical science and other groups including experimental activities. If anyone would like to invite speakers, please contact Liang (lianghsu@princeton.edu). The members in our group are encouraged to give a presentation.

(3) Time and Location: The meeting program is currently scheduled to be held in 281 at 3:00 pm each Thursday (in principle).

Speakers and Topics:

9/10 Herschel Rabitz (Professor, theoretical, Chemistry)
Topic: Control in the Sciences over Vast Length and Time Scales
The control of physical, chemical, and biological phenomena are pervasive in the sciences. The dynamics involved span vast length and time scales with the associated controls ranging from shaped laser pulses out to the application of special chemical reagents and processing conditions. Despite all of these differences, there is clear common behavior found upon seeking optimal control in these various domains. Evidence of this common behavior will be presented from the control of quantum, chemical, and biological processes. The most evident finding is that control efforts can easily beat the so-called “curse of dimensionality” upon satisfaction of assumptions that are expected to widely hold. Quantum phenomena provide a setting to quantitatively test the control principles. The potential consequences of the observations will be discussed.
 9/17 Shahnawaz R. Rather (Postdoctoral Associate, experimental, Schole’s group, Chemistry)
Topic: Observing Vibrational Wavepackets during an Ultrafast Electron Transfer Reaction
Abstract: Recent work has proposed that coherent effects impact ultrafast electron transfer reactions. Here we report studies using broadband pump probe and two-dimensional electronic spectroscopy of intramolecular nuclear motion on the time scale of the electron transfer between oxazine 1 (Ox1) and dimethylaniline (DMA) solvent that acts as the electron donor. We performed time-frequency analysis on the time domain data to assign signal amplitude modulations to ground or excited electronic states in the reactive system (Ox1 in DMA) relative to the control system (Ox1 in chloronaphthalene). It was found that our ability to detect vibrational coherence via the excited electronic state of Ox1 diminishes on the timescale that population is lost by electron transfer. However, the vibrational wavepacket is not damped by the electron transfer process and has been observed previously by detecting the Ox1 radical transient absorption. The vibrational coherence is therefore essentially a spectator during the electron transfer process, consistent with a Born-Oppenheimer separation of electronic and nuclear degrees of freedom, but nevertheless intramolecular vibrations (not coherence per se) can influence the rate of electron transfer.
 9/24 Jacob Dean (Postdoctoral Associate, experimental, Schole’s group, Chemistry)
Topic: Have your cake and eat it too: Applications of coherent spectroscopy to photo-induced dynamics and molecular structure
Abstract: Since the advent of tabletop ultrafast laser sources, the events that follow photon absorption have been investigated at ever-increasing time resolution. The result of this development has been the “real-time” observation of molecular processes (radiative and non-radiative) outlined in the Jablonski diagram, which can occur on the picosecond to sub-picosecond timescale. Such studies are typically done in the pump-probe format where a pump pulse induces a specific excitation in the system and a probe pulse interrogates the state of the system at each time delay. As the pulse duration is decreased well below 100 femtoseconds however, the spectrum of the employed pulses increasingly broadens and the excitation can span multiple quantum states (electronic, vibrational, etc.) leading to a coherent superposition of excited eigenstates, or a wavepacket. The resulting signals from such excitation conditions evolve in time either as populations (incoherent dynamics) or coherences, which appear as oscillatory signal amplitude. Vibrational coherences generated by excitation with pulses shorter than a vibrational period, yield time-domain oscillations characteristic of the frequency and amplitude of the corresponding modes activated, which inherently report on the chromophores’ potential energy surfaces. Nonlinear techniques such as broadband pump-probe and two-dimensional electronic spectroscopy are highly sensitive to both population and oscillatory dynamics, and their utility will be discussed toward applications in molecular photophysics/photochemistry, as well as chromophore structure and vibronic spectroscopy in the condensed phase. Namely, work relating to photosynthetic protein complexes and model dyes will be discussed.

Carlee Joe-Wong (PhD Candidate, theoretical, Applied and Computational Mathematics)
Topic: Optimal Control Landscapes for Molecules Described by Classical Mechanics
Abstract: We consider laser-driven optimal control of a molecule whose dynamics can be described by classical (Hamiltonian) mechanics. The molecule’s state evolves under control for a fixed time interval. We define an objective function of the final molecular state (e.g., steering the final state to a given target) and take the control landscape to be the objective as a functional of the control field. We then assess two characteristics of the landscape: first, does it contain any traps, and second, how smooth is it? The first question can be answered by examining the landscape gradient and Hessian with respect to the control. Under particular assumptions, the control landscape is found to be free of traps that could hinder reaching the objective. The Hessian associated with an optimal control field is shown to have finite rank, indicating an inherent degree of robustness to control noise. The second question can be studied through examining the path of the control field from its initial to optimal value. We find that the path length is generally quite short, comparable to that of a straight-shot linear path from the initial to optimal fields. This result indicates that the landscape is smooth: instead of taking a long, circuitous path to climb the landscape, the control field can efficiently follow a close-to-linear path towards an optimal field. Numerical simulations are presented to illustrate the theoretical landscape principles.

 10/01 Denys I. Bondar (Postdoctoral Associate, theoretical, Rabitz’s group, Chemistry)
Topic: Measurement driven modeling of quantum and classical dynamical systems
Abstract: In this talk, we will provide an answer to the question: “What kind of observations and assumptions are minimally needed to formulate a physical theory?” Our answer to this question leads to the new systematic approach of Operational Dynamical Modeling (ODM), which allows to deduce equations of motions from time evolution of observables. Using ODM, we are not only able to re-derive well-known physical theories (such as the Schrodinger and classical Liouville equations), but also infer novel physical dynamics in the realm of non-equilibrium quantum statistical mechanics, shedding light on controversial and open questions.
 10/08 Renan Cabrera (Postdoctoral Associate, theoretical, Rabitz’s group, Chemistry)
Topic: Efficient simulation of open quantum systems
Abstract: The simulation of realistic quantum systems may require the introduction of open systems interactions, where the use of the traditional wave function is not sufficient. This talk illustrates some of our recent developments to simulate open quantum systems in terms of the Wigner function and the density matrix in general. These techniques are employed to simulate non-relativistic quantum systems but are also applied to non-linear and open relativistic quantum systems for single and two-particle systems. Current developments are very promising to extend the applicability to higher dimensions and even more diverse systems.
 10/15  Yanbing Liu (PhD Candidate, experimental, Houck’s group, Electrical Engineering)
Topic: Reservoir Engineering in Circuit Quantum Electrodynamics
Abstract: Quantum electrodynamics(QED) studies the fundamental interaction between electrons/atoms and light. In circuit QED experiments, ‘atoms’ and ‘light’ are quantized excitations of superconducting electrical circuits, constructed in a modular manner with modern lithographic techniques. This field receives a lot of attention in recent years (IBM, Google, Intel, …) due to the promise of building a universal quantum computer. However, in this talk, I will show that circuit QED provides an ideal platform for novel physics in quantum optics, as the lithographic nature of circuit design enables a powerful range of experiments otherwise unreachable in conventional optical systems. Specifically, I will show how basic QED processes such as spontaneous emission and resonance fluorescence will change when an ‘atom’ is strongly coupled to band-gap medium or a multimode cavity.
 10/22 Timothy Berkelbach (Postdoctoral Fellow, theoretical, Princeton Center for Theoretical Science)
 10/29  Joshua Kretchmer (Postdoctoral Associate, theoretical, Chan’s group, Chemistry)
 11/05 fall break
 11/12 Fausto Martelli (Postdoctoral Associate, theoretical, Car’s group, Chemistry)
11/19 Zachary Quine (PhD candidate, experimental, Rabitz’s group, Chemistry)
Wei-Hsiang Lin (Postdoctoral Associate, experiment + theory, Biology, NYU)
11/26 Yinyu Liu (PhD Candidate, experimental, Petta’s group, Physics)
12/03 Margherita Maiuri (Postdoctoral Fellow, experimental, Schole’s group, Chemistry)
12/10 David Limmer (Postdoctoral Fellow, theoretical, Princeton Center for Theoretical Science),BR>
Liang-Yan Hsu (Postdoctoral Associate, theoretical, Rabitz’s group, Chemistry)