"Spectroscopy of Molecular Aggregates & Many-body Decoherence" Aurelia Chenu

Speaker: Dr. Aurelia Chenu, Postdoc Research Fellow, Massachusetts Institute of Technology, USA

Title: Spectroscopy of Molecular Aggregates & Many-body Decoherence

Abstract:
Nature has mastered the art of molecular self-assembly, evolving from a very limited number of building blocks an impressive diversity of photosynthetic light-harvesting complexes, which are highly versatile and efficient. Understanding the sensitive interplay between the self-assembled superstructures and their functional properties is highly desirable for the synthesis of new materials, the design and operation of organic-based devices. I will present a systematic method that establishes such a link, and present a relationship between molecular superstructures and their optical and transport properties [1]. This model allows one to predict the physical properties of complex structures and, conversely, infer the structure from its measured properties. In addition, it provides a practical method to compute spectra and transfer rates in multichromophoric systems from experimentally accessible monomer data.

I shall then focus on dynamical properties of the photosyntetic aggregates, modeled as open quantum systems and [2] propose a theory explaining the origins of long-lived coherences observed in their 2D electronic spectra, [3] show the influence of excitation conditions on the open dynamics and [4-5] present how to mimic natural excitation in the lab, i.e. how incoherent sunlight relates to coherent laser pulses. This relies on a new formalism, based on thermally excited wave packets, that provides the missing link for a continuous connection between classical and quantum representations of a thermal gas [6].

In a last part, I will introduce a scheme for the quantum simulation of many-body decoherence, which is based on the unitary evolution of a stochastic Hamiltonian [7]. I will show how to simulate an effectively open dynamics governed by k-body Lindblad operator, following Markovian or non-Markovian dynamics, and provide the time scale governing the fidelity decay. Such scheme exhibits a strong signature of many-body decoherence, and can be readily implemented in current quantum platforms.

References:
[1] A. Chenu and J. Cao, Phys. Rev. Lett. 118:013001  (2017)
[2] A. Chenu, N. Christensson, H. Kauffmann and T. Mancal, Sci. Rep. 3:2029 (2013)
[3] A. Chenu, P. Maly and T. Mancal, Chem. Phys. 439:100 (2014)
[4] A. Chenu, A. Branczyk, G. Scholes and J. Sipe, Phys. Rev. Lett. 114:213601 (2015)
[5] A. Chenu and P. Brumer, J. Chem. Phys. 144:044103 (2016)
[6] A. Chenu and M. Combescot, Phys. Rev. A, arXiv:1703.03828 (2017)
[7] A. Chenu, M. Beau, J. Cao and A. del Campo, Phys. Rev. Lett. 118:140403 (2017)