arXiv subjects

Andrew M. Moran

Publications and source records attributed to Andrew M. Moran.

5 recordsLinked to original sources

arXiv2026

Nonlinear Optical Quantum Communication with a Two-Dimensional Perovskite Light Source

Two-dimensional organic-inorganic hybrid perovskite (2D-OIHP) quantum wells are emerging as promising light sources for quantum communication technologies, owing to their ability to generate polarization-encoded optical signals. In this work, we explore how nonlinear optical phenomena can be exploited for quantum information applications, demonstrating the versatility that arises from resonant coupling among excited states. By tracking changes in the ellipticities of signal photons on femtosecond timescales in four-wave-mixing experiments, we first establish a method for information encoding based on exciton spin dynamics and biexciton correlations. Using single-photon detection, we then implement a proof-of-principle quantum communication protocol by mapping these polarization states onto binary sequences. While the polarizations of weak coherent pulses are typically manipulated with optical elements in traditional quantum key distribution approaches, the intrinsic electronic structure and spin relaxation processes within the 2D-OIHP system determine the characteristics of the signal photons in our method. As a demonstration, an ASCII message consisting of 56 bits is transmitted through the polarization states of photons emitted by 2D-OIHP quantum wells. These results show that the information transmission efficiency depends strongly on contributions from biexciton states, highlighting the potential of spin-dependent nonlinear optical processes for quantum communication.

quant-ph↗

arXiv2026

Poincaré Sphere Representation of Spin-Driven Polarization Encoding in Two-Dimensional Perovskite Light Sources

Nonlinear optical light sources enable the generation of photons with polarization states that are intrinsically determined by underlying material dynamics, rather than imposed through external modulation. Here, we investigate the fundamental quantum communication performance achievable using four-wave-mixing signal fields emitted by a representative two-dimensional perovskite system. The experimentally reconstructed signal field is represented by Stokes-vector trajectories on the Poincaré sphere to establish a practical framework for visualizing spin-driven polarization encoding. An empirical nonlinear response model further connects the properties of the signal field to microscopic exciton and biexciton electronic structure, revealing that interference between resonantly enhanced optical transitions governs the accessible polarization states. The model additionally predicts that modest stabilization of the lowest-energy biexciton could substantially improve the polarization-encoding performance and provide a route toward materials optimization. More broadly, these results motivate closer integration of nonlinear spectroscopy, semiconductor materials, and quantum information science in the development of novel light sources for quantum communication.

quant-ph↗

arXiv2026

Quantitative Analysis of Exciton Composition and Dynamics in Y6 Films for Single-Component Solar Cells

Non-fullerene acceptors such as Y6 have enabled high-efficiency organic photovoltaic devices and motivated the development of single-component architectures; however, the microscopic mechanisms governing exciton transport and charge dissociation remain under active investigation. In particular, the interplay between Frenkel-charge-transfer excitations and their coupling to environmental fluctuations complicates the description of light absorption and subsequent exciton dynamics. Here, ultrafast transient absorption spectroscopy is used to probe exciton quenching dynamics in Y6 films interfaced with hole-transport layers. To interpret these measurements, we develop an analytical model based on hybrid Frenkel-charge-transfer states that enables direct extraction of intermolecular electronic couplings, charge-transfer character, and system-bath interaction strengths from experimental data. The analysis reveals a substantial charge-transfer admixture of 20-40% in the exciton states and identifies a transport regime characterized by delocalization-mediated exciton motion rather than purely diffusive hopping. Consistent with this interpretation, the corresponding quenching dynamics occur on a ~1 ps timescale within ~4 nm of the interface, suggesting a short-range injection mechanism facilitated by exciton delocalization. In addition to providing physical parameters for Y6, these results establish a quantitative framework that connects spectroscopic observables to microscopic transport mechanisms and can be generalized to other non-fullerene acceptors.

physics.chem-ph↗

arXiv2026

Visualization-Based Approach to Condensed-Phase Line Broadening Using Polyene Chains

Condensed-phase spectral line shapes encode the strength and timescale of interactions between molecules and their environments, yet these ideas are often difficult to introduce at the undergraduate level due to their reliance on formal theoretical treatments. We present a visualization-based approach that combines analytic results with numerical simulations to illustrate the physical origins of spectral line broadening in conjugated molecular systems. Using a time-dependent Hückel Hamiltonian, we derive closed-form expressions for coherent electronic motion in finite polyene chains and show how these results provide direct insight into the role of molecular orbital structure in light absorption. Environmental effects are introduced through stochastic fluctuations of the Hamiltonian matrix elements, allowing students to observe how system--environment interactions disrupt coherent motion and produce scattering-like features in electronic trajectories. Real-space animations and simulated absorption spectra provide an intuitive link between microscopic dynamics and measured line shapes. The MATLAB code provided with this work offers an accessible platform for integrating computation and visualization into undergraduate instruction while introducing key concepts in condensed-phase spectroscopy.

physics.chem-ph↗

arXiv2022

A Quantitative Model of Charge Injection by Ruthenium Chromophores Connecting Femtosecond to Continuous Irradiance Conditions

A kinetic framework for the ultrafast photophysics of tris(2,2-bipyridine)ruthenium(II) phosphonated and methyl-phosphonated derivatives is used as a basis for modeling charge injection by ruthenium dyes into a semiconductor substrate. By including the effects of light scattering, dye diffusion and adsorption kinetics during sample preparation, and the optical response of oxidized dyes, quantitative agreement with multiple transient absorption datasets is achieved on timescales spanning femtoseconds to nanoseconds. In particular, quantitative agreement with important spectroscopic handles, decay of an excited state absorption signal component associated with charge injection in the UV region of the spectrum and the dynamical redshift of an approximately 500 nm isosbestic point, validates our kinetic model. Pseudo-first-order rate coefficients for charge injection are estimated in this work, with an order of magnitude ranging 1011 s-1 to 1012 s-1. The model makes the minimalist assumption that all excited states of a particular dye have the same charge injection coefficient, an assumption that would benefit from additional theoretical and experimental exploration. We have adapted this kinetic model to predict charge injection under continuous solar irradiation, and find that as many as 68 electron transfer events per dye per second take place, significantly more than prior estimates in the literature.

physics.chem-ph↗