Quantum Energy Diffusion in Polaritonic Wires Pubblico
Kairys, Kyle (Spring 2022)
Abstract
The worsening climate crisis has place d increased emphasis on the development of novel modes of sustainable energy generation and transport. A major inhibi tion to this process is the fast and efficient transport of energy. Quantum energetic phenomena of organic polariton s in op tical microcavities have demonstrated significant potential to revolutionize m odes of energy transfer. In this wo rk, the de finition of short-time, spat ial diff usion was investigated for these systems and their cohe rent energy transfer dynamics. This investigation implemented a microscopically detailed computational photonic wi re model that evaluates spacetime resolved ene rgy dif fusion . All simulation s conducted employ ed the use of an initial state described by a molecular excited-state Gaussian wavepacket . This study m odula ted al terat ions to the internal system parameters of light-matter coupling strength, total system size, and variance of molecular excited-state energy fluctuations . This was done to effectively elucidate their impact on the intermolecular energy transport of the polaritonic sys tem. In the absence of fluctuations in the molecular excited-state energies, ballistic intermolecular energy transport dynamics were observed within the femtosecond timescale; this observation however was not upheld for systems with energetic disorder. Diffusion constants were simulated for systems experiencing strong and weak energetic disorder. Within the strong disorder case, the introduction of disorder above a specific critical value of the light-matter interaction, resulted in the excited states of the system to become highly localized and trap the energy. This observation was upheld for a 20-picosecond time scale. In the case of weak disorder, relative to the light-matter interaction strength, diffusion constants increase as the disorder of the system is decreased. Through evaluation of molecular density, it was determined that a smaller system density results in increased transport properties because the single molecular dipole moments scale with intermolecular distances. It was also determined that for sufficiently small intermolecular distances, simulated diffusion constants were seemingly independent of system size, however with larger intermolecular distances there appeared to be a significant transport dependence on system size. This investigation has evaluated novel properties of quantum intermolecular energy transport in photonic wires, and it has determined that such behavior is relatively controllable through the characteristics of polaritonic devices. This demonstrates significant potential for the control of molecular material dynamics in optical cavities.
Table of Contents
Table of Contents
1. General Background
1.1. Energy Transport..................................................................................10
1.2. Polaritonic Systems................................................................................11
1.2.1. Optical Microcavities.....................................................................12
1.2.2. Light-Matter Coupling Strength.........................................................14
1.3. Energetic Diffusion................................................................................15
2. Computational Methods
2.1. Physical Model.....................................................................................16
2.1.1. Photonic Wire Model.....................................................................16
2.1.2. Molecular System.........................................................................18
2.2. Hamiltonian Definition...........................................................................20
2.3. Time Evolution....................................................................................22
2.4. Initial State..........................................................................................24
2.5. Energy Transport Observables..................................................................25
2.5.1. Short Time Propagation ..................................................................26
2.5.2. Diffusion Constant........................................................................27
3. Ideal Model
3.1. Introduction.........................................................................................30
3.2. Ballistic Motion....................................................................................31
3.3. Subsystem Energy Localization..................................................................33
4. Microscopic Models with Disorder
4.1. Introduction..........................................................................................35
4.2. Energy Transport Dependence on Light-Matter Coupling Strength........................37
4.3. Energy Transport Dependence on Number of Molecules....................................39
4.4. Diffusion Constants under Strong Disorder....................................................40
4.5. Diffusion Constants under Weak Disorder......................................................42
5. Density Dependence....................................................................................44
6. Summary and Conclusions.............................................................................46
7. References................................................................................................51
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