arXiv subjects

Eric R. Bittner

Publications and source records attributed to Eric R. Bittner.

At least 55 records · Page 3Linked to original sources

arXiv2021

Freezing molecules with light: How long can one maintain a non-equilibrium molecular geometry by strong light-matter coupling?

In molecular photochemistry, the non-equilibrium character and subsequent ultrafast relaxation dynamics of photoexcitations near the Franck-Condon region limit the control of their chemical reactivity. We address how to harness strong light-matter coupling in optical microcavities to isolate and preferentially select specific reaction pathways out of the myriad of possibilities present in large-scale complex systems. Using Fermi's Golden Rule and realistic molecular parameters, we estimate the extent to which molecular configurations can be "locked" into non-equilibrium excited state configurations for timescales well beyond their natural relaxation times. For upper polaritons--which are largely excitonic in character, molecular systems can be locked into their ground state geometries for tens to thousands of picoseconds and varies with the strength of the exciton/phonon coupling (Huang-Rhys parameter). On the other hand, relaxed LP lifetimes are nearly uniformly distributed between 2.1-2.4\,ps and are nearly independent of the Huang-Rhys parameter.

physics.chem-ph↗

arXiv2020

Stochastic scattering theory for excitation induced dephasing: Time-dependent nonlinear coherent exciton lineshapes

We develop a stochastic theory that treats time-dependent exciton-exciton s-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model excitation-induced dephasing effects on time-resolved two-dimensional coherent optical lineshapes and we identify a number of features that can be attributed to the many-body dynamics occurring in the background of the exciton, including dynamic line narrowing, mixing of real and imaginary spectral components, and multi-quantum states. We test the model by means of multidimensional coherent spectroscopy on a two-dimensional metal-halide semiconductor that hosts tightly bound excitons and biexcitons that feature strong polaronic character. We find that the exciton nonlinear coherent lineshape reflects many-body correlations that give rise to excitation-induced dephasing. Furthermore, we observe that the exciton lineshape evolves with population time over time windows in which the population itself is static, in a manner that reveals the evolution of the multi-exciton many-body couplings. Specifically, the dephasing dynamics slow down with time, at a rate that is governed by the strength of exciton many-body interactions and on the dynamic Coulomb screening potential. The real part of the coherent optical lineshape displays strong dispersive character at zero time, which transforms to an absorptive lineshape on the dissipation timescale of excitation-induced dephasing effects, while the imaginary part displays converse behavior. Our microscopic theoretical approach is sufficiently flexible to allow for a wide exploration of how system-bath dynamics contribute to linear and non-linear time-resolved spectral behavior.

physics.chem-ph↗

arXiv2020

Stochastic scattering theory for excitation induced dephasing: Comparison to the Anderson-Kubo lineshape

In this paper we present a quantum stochastic model for spectroscopic line-shapes in the presence of a co-evolving and non-stationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scattering as mediated by their screened Coulomb coupling. The Heisenberg equations of motion for the optical excitons are then driven by an auxiliary stochastic population variable, which we take to be the solution of an Ornstein-Uhlenbeck process. Itô's Lemma then allows us to easily construct and evaluate correlation functions and response functions. Focusing on the linear response, we compare our model to the classic Anderson-Kubo model. While similar in motivation, there are profound differences in the predicted lineshapes, notably in terms of asymmetry, and variation with increasing background population.

physics.chem-ph↗

arXiv2020

Probing exciton/exciton interactions with entangled photons: theory

Quantum entangled photons provide a sensitive probe of many-body interactions and offer an unique experimental portal for quantifying many-body correlations in a material system. In this paper, we present a theoretical demonstration of how photon-photon entanglement can be generated via interactions between coupled qubits. Here we develop a model for the scattering of an entangled pair of photons from a molecular dimer. We develop a diagrammatic theory for the scattering matrix and show that one can correlate the von Neumann entropy of the outgoing bi-photon wave function to exciton exchange and repulsion interactions. We conclude by discussing possible experimental scenarios for realizing these ideas.

quant-ph↗

arXiv2020

Non-equilibrium states of a plasmonic Dicke model with coherent and dissipative surface plasmon-quantum emitter interactions

Hybrid photonic-plasmonic nanostructures allow one to engineer coupling of quantum emitters and cavity modes accounting for the direct coherent and environment mediated dissipative pathways. Using generalized plasmonic Dicke model, we explore the non-equilibrium phase diagram with respect to these interactions. The analysis shows that their interplay results in the extension of the superradiant and regular lasing states to the dissipative coupling regime and an emergent lasing phase without population inversion having boundary with the superradiant and normal states. Calculated photon emission spectra are demonstrated to carry distinct signatures of these phases.

cond-mat.mes-hall↗

arXiv2019

Quantum process tomography of entangled photons as a probe of intermediates of singlet fission in a tetracene derivative

Spin-entaglement has been proposed and extensively used in the case of correlated triplet pairs which are intermediate states in singlet fission process in select organic semiconductors. Here, we employ quantum process tomography of polarization entangled photon-pairs resonant with the excited state absorption of these states to investigate the nature of the inherent quantum correlations and to explore for an unambiguous proof for the existence of exciton entanglement.

physics.chem-ph↗

arXiv2019

Electron-phonon couplings inherent in polarons drive exciton dynamics in two-dimensional metal-halide perovskites

We report on the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite. We probe the time evolution of four distinct exciton resonances by means of time-resolved photoluminescence and transient absorption spectroscopies, and find that at 5\,K a subset of excitons form on a $\lesssim$ 1-ps timescale, and that these relax subsequently to lower-energy excitons on $\sim$ 5--10\,ps with a marked temperature dependence over $<$ 100\,K. We implement a mode projection analysis that determines the relative contribution of all observed phonons with frequency $\leq$50\,cm$^{-1}$ to inter-exciton nonadiabatic coupling, which in turn determines the rate of exciton relaxation. This analysis ranks the relative contribution of the phonons that participate in polaronic lattice distortions to the exciton inter-conversion dynamics and thus establishes their role in the nonadiabatic mixing of exciton states, and this in the exciton relaxation rate.

cond-mat.mtrl-sci↗

arXiv2018

Photon entanglement entropy as a probe of many-body correlations and fluctuations

Recent theoretical and experiments have explored the use of entangled photons as a spectroscopic probe of material systems. We develop here a theoretical description for entropy production in the scattering of an entangled biphoton state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matrix in terms of single-photon terms in which we introduce the photon-photon interaction via a complex coupling constant, $ξ$. We show that the von Neumann entropy provides a succinct measure of this interaction. We then develop a microscopic model and show that in the limit of fast fluctuations, the entanglement entropy vanishes whereas in the limit the coupling is homogeneous broadened, the entanglement entropy depends upon the magnitude of the fluctuations and reaches a maximum.

quant-ph↗

arXiv2017

Probing dynamical symmetry breaking using quantum-entangled photons

We present an input/output analysis of photon-correlation experiments whereby a quantum mechanically entangled bi-photon state interacts with a material sample placed in one arm of a Hong-Ou-Mandel (HOM) apparatus. We show that the output signal contains detailed information about subsequent entanglement with the microscopic quantum states in the sample. In particular, we apply the method to an ensemble of emitters interacting with a common photon mode within the open-system Dicke Model. Our results indicate considerable dynamical information concerning spontaneous symmetry breaking can be revealed with such an experimental system.

quant-ph↗

arXiv2017

Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors

We measure the homogeneous excitation linewidth of regioregular poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by means of two-dimensional coherent photoluminescence excitation spectroscopy. At a temperature of 8\,K, we find a linewidth that is always $\gtrsim 110$\,meV full-width-at-half-maximum, which is a significant fraction of the total linewidth. It displays a spectral dependence and is minimum near the 0--0 origin peak. We interpret this spectral dependence of the homogeneous excitation linewidth within the context of a weakly coupled aggregate model.

cond-mat.mtrl-sci↗

arXiv2016

Quantum simulations of charge-separation at a model donor-acceptor interface: role of delocalization and local packing

We investigate the electronic dynamics of a model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and a [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide and estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We show that the electronic dynamics of the OPV are dramatically altered by varying the positions of the molecules simulated at the interface. The lowest few excited states of the model interface rapidly mix allowing low frequency C-C out of plain torsions to modulate the potential energy surface such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on sub 100 fs time scales. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.

cond-mat.mtrl-sci↗

arXiv2016

Inelastic Charge Transfer Dynamics in Donor-Bridge-Acceptor Systems Using Optimal Modes

We present a novel {\em ab initio} approach for computing intramolecular charge and energy transfer rates based upon a projection operator scheme that parses out specific internal nuclear motions that accompany the electronic transition. Our approach concentrates the coupling between the electronic and nuclear degrees of freedom into a small number of reduced harmonic modes that can be written as linear combinations of the vibrational normal modes of the molecular system about a given electronic minima. Using a time-convolutionless master-equation approach, parameterized by accurate quantum-chemical methods, we benchmark the approach against experimental results and predictions from Marcus theory for triplet energy transfer for a series of donor-bridge-acceptor systems. We find that using only a single reduced mode--termed the "primary" mode, one obtains an accurate evaluation of the golden-rule rate constant and insight into the nuclear motions responsible for coupling the initial and final electronic states. We demonstrate the utility of the approach by computing the inelastic electronic transition rates in a model donor-bridge-acceptor complex that has been experimentally shown that its exciton transfer pathway can be radically modified by mode-specific infrared excitation of its vibrational mode.

cond-mat.mtrl-sci↗

arXiv2015

Quantum symmetry breaking of exciton/polaritons in metal-nanorod plasmonic array

We study the collective, superradiant behavior in the system of emitter-dressed Ag nanorods. Starting from the Drude model for the plasmon oscillations, we arrive at a semi-empirical Hamiltonian describing the coupling between quantized surface plasmon modes and the quantum emitters that can be controlled by manipulating their geometry, spacing, and orientation. Further, identifying the lowest polariton mode as SP-states dressed by excitons in the vicinity of $k=0$, we examine conditions allowing for the polariton quantum phase transition. While the system is formally a 1D array, we show that the polariton states of interest can undergo a quantum phase transition to form a Bose condensate at finite temperatures for physically accessible parameter ranges.

cond-mat.mes-hall↗

arXiv2015

Role of structural fluctuations and environmental noise in the electron/hole separation kinetics at organic polymer bulk-heterojunction interfaces

We investigate the electronic dynamics of model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed by C=C bond fluctuations such that the system can sample both intermolecular charge-transfer and charge-separated electronic configurations on a time scale of 20fs. Our simulations support an emerging picture of carrier generation in OPV systems in which interfacial electronic states can rapidly decay into charge-separated and current producing states via coupling to vibronic degrees of freedom.

cond-mat.mtrl-sci↗

arXiv2015

Two-dimensional coherent photocurrent excitation spectroscopy in a polymer solar cell

In high-performance solar cells based on polymeric semiconductors, the mechanism of photocarrier generation on $<100$-fs timescales is yet to be unravelled. In particular the dynamics of early-time electronic coupling between excitons on polymer chains and charge-transfer states need to be investigated in order to develop a detailed picture of ultrafast processes involved in photocurrent production. In this proceeding, we report preliminary measurements using a novel spectroscopy that can measure such correlations: two-dimensional coherent photocurrent excitation spectroscopy. This nonlinear technique measures off-diagonal spectral correlations in a two-dimensional photocurrent excitation spectrum. We interpret these sectroscopic measurements in light of recent theoretical predictions.

cond-mat.mtrl-sci↗

arXiv2013

Noise-induced quantum coherence drives photocarrier generation dynamics at polymeric semiconductor heterojunctions

We present a fully quantum-mechanical model of the electronic dynamics of primary photoexcitations in a polymeric semiconductor heterojunction, which includes both polymer stacking and phonon relaxation. By examining the phonon-induced fluctuations in the state-to-state energy gaps and the exact golden-rule rate constants, we conclude that resonant tunnelling between the primary exciton to delocalized interchain charge-transfer states may be the initial step in the formation of charge-carriers in polymer-based bulk-heterojunction photovoltaic diodes.

cond-mat.mtrl-sci↗

arXiv2013

Exciton fission via ultrafast long-range resonant tunnelling in organic photovoltaic diodes

We present an exciton/lattice model of the electronic dynamics of primary photoexcitations in a polymeric semiconductor heterojunction which includes both polymer pi-stacking, energetic disorder, and phonon relaxation. Results from our model are consistent with a wide range of recent experimental evidence that excitons decay directly to well-defined polarons on a sub-100 fs timescale, which is substantially faster than exciton relaxation processes. Averaging over multiple samples, we find that as the interfacial offset is increased, a substantial fraction of the density of electronic states in the energy region about the initial exciton carries significant charge-transfer character with two charges separated in the outer regions of the model lattice. The results indicate a slight increase in the density of such current-producing states if the region close to the interface is more disordered. However, since their density of states overlaps the excitation line-shape of the primary exciton, we show that it is possible that the exciton can decay directly into current-producing states via tunneling on an ultrafast time-scale. We find this process to be independent of the location of energetic disorder in the system, and hence we expect exciton fission via resonant tunnelling to be a ubiquitous feature of these systems.

cond-mat.mtrl-sci↗

arXiv2012

Quantum Origins of Molecular Recognition and Olfaction in Drosophila

The standard model for molecular recognition of an odorant is that receptor sites discriminate by molecular geometry as evidenced that two chiral molecules may smell very differently. However, recent studies of isotopically labeled olfactants indicate that there may be a molecular vibration-sensing component to olfactory reception, specifically in the spectral region around 2300 cm$^{-1}$. Here we present a donor-bridge-acceptor model for olfaction which attempts to explain this effect. Our model, based upon accurate quantum chemical calculations of the olfactant (bridge) in its neutral and ionized states, posits that internal modes of the olfactant are excited impulsively during hole transfer from a donor to acceptor site on the receptor, specifically those modes that are resonant with the tunneling gap. By projecting the impulsive force onto the internal modes, we can determine which modes are excited at a given value of the donor-acceptor tunneling gap. Only those modes resonant with the tunneling gap and are impulsively excited will give a significant contribution to the inelastic transfer rate. Using acetophenone as a test case, our model and experiments on D. melanogaster suggest that isotopomers of a given olfactant give rise to different odorant qualities. These results support the notion that inelastic scattering effects play a role in discriminating between isotopomers, but that this is not a general spectroscopic effect

physics.bio-ph↗