Quantum Dynamics Research Group


The Quantum Dynamics Research Group focuses on developing novel computational approaches to simulating non-equilibrium dynamics of quantum systems in the condensed phase, overcoming the curse of dimensionality.



Quantum Dynamics Research Group

Announcements

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  • Postdoctoral, PhD and project positions are available in our group. Join Us.

  • October 2024: Devansh’s exploration of the effect of loss mechanisms on linear spectra using our Path Integral Lindblad Dynamics method published in the Journal of Chemical Theory and Computation. Congratulations! Check it out…

  • March 2024: A novel and efficient approach to incorporating empirical gain / loss mechanisms into numerically exact, non-perturbative path integral simulations of open quantum systems published in the Journal of Physical Chemistry Letters. Check it out…

  • December 2023: A new tensor network approach to simulating quantum correlation functions published in the Journal of Chemical Physics. Check it out…

  • September 2023: Study of excitonic dynamics and pathways in the Fenna-Matthews-Olson complex published in the Journal of Physical Chemistry B. Check it out…

  • August 2023: Work on identifying pathways of quantum transport in molecular aggregates published in the Journal of Chemical Theory and Computation. Check it out…

  • May 2023: Package for simulating quantum dynamics in complex open systems package with support for a number of state-of-the-art methods published in the Journal of Chemical Physics. Check it out…

Research Areas

The cost of simulations of time-evolution of quantum systems grows exponentially with the number of dimensions involved. Various approaches, both approximate and numerically exact, are required to make such simulations feasible. Explore the ideas that are being developed in the group.

Recent Publications

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Quickly explore the developments by searching through the publications.
Impact of Loss Mechanisms on Linear Spectra of Excitonic and Polaritonic Aggregates
Impact of Loss Mechanisms on Linear Spectra of Excitonic and Polaritonic Aggregates

The presence of loss mechanisms governed by empirical timescales can profoundly affect the dynamics in molecular systems, leading to changes in their spectra. However, incorporation of these effects along with the system’s interaction with the thermal dissipative environments proves to be challenging. In this work, we demonstrate the possibility of utilizing the recently developed path integral Lindblad dynamics (PILD) method to study the linear spectra of molecular aggregates. PILD presents a uniquely powerful simulation technique for retaining the effects of the vibrations in a numerically exact manner through the Feynman–Vernon influence functional while incorporating the effects of losses in an empirical manner using the Lindbald master equation. As illustrations of this technique, we provide examples taken from chiral excitonic and polaritonic aggregates for which we simulate both the absorption spectra and circular dichroism (CD) spectra. We demonstrate that the effect of loss on particular states can differ not just on the basis of the symmetries of the state but also on the basis of complicated “interactions” of the structured dissipative environments with the system and its loss mechanisms. Due to the different selection rules between the absorption and CD spectra and the relative intensities and broadening of the peaks, the two linear spectra together give an interesting insight into the contributions of the various eigenstates to the correlation functions. While the focus here is on linear spectroscopy, it should be possible in the future to use PILD to study multidimensional spectra under loss mechanisms as well.

Impact of Spatial Inhomogeneity on Excitation Energy Transport in the Fenna–Matthews–Olson Complex
Impact of Spatial Inhomogeneity on Excitation Energy Transport in the Fenna–Matthews–Olson Complex

The dynamics of the excitation energy transfer (EET) in photosynthetic complexes is an interesting question both from the perspective of fundamental understanding and the research in artificial photosynthesis. Over the past decade, very accurate spectral densities have been developed to capture spatial inhomogeneities in the Fenna–Matthews–Olson (FMO) complex. However, challenges persist in numerically simulating these systems, both in terms of parameterizing them and following their dynamics over long periods of time because of long non-Markovian memories. We investigate the dynamics of FMO with the exact treatment of various theoretical spectral densities using the new tensor network path integral-based methods, which are uniquely capable of addressing the difficulty of long memory length and incoherent Förster theory. It is also important to be able to analyze the pathway of EET flow, which can be difficult to identify given the non-trivial structure of connections between bacteriochlorophyll molecules in FMO. We use the recently introduced ideas of relating coherence to population derivatives to analyze the transport process and reveal some new routes of transport. The combination of exact and approximate methods sheds light on the role of coherences in affecting the fine details of the transport and promises to be a powerful toolbox for future exploration of other open systems with quantum transport.

Impact of Solvent on State-to-State Population Transport in Multistate Systems Using Coherences
Impact of Solvent on State-to-State Population Transport in Multistate Systems Using Coherences

Understanding the pathways taken by a quantum particle during a transport process is an enormous challenge. There are broadly two different aspects of the problem that affect the route taken. First is obviously the couplings between the various sites, which translates into the intrinsic “strength” of a state-to-state channel. Apart from these inter-state couplings, the relative coupling strengths and timescales of the solvent modes form the second factor. This impact of the dissipative environment is significantly more difficult to analyze. Building on the recently derived relations between coherences and population derivatives, we present an analysis of the transport that allows us to account for both the effects in a rigorous manner. We demonstrate the richness hidden behind the transport even for a relatively simple system, a 4-site coarse-grained model of the Fenna–Matthews–Olson complex. The effect of the local dissipative media is highly nontrivial. We show that while the impact on the total site population may be small, there are noticeable changes to the pathway taken by the transport process. We also demonstrate how an analysis in a similar spirit can be done using the Förster approximation. The ability to untangle the dynamics at a greater granularity opens up possibilities in terms of design of novel systems with an eye toward quantum control.