arXiv subjects

Eran Rabani

Publications and source records attributed to Eran Rabani.

At least 19 recordsLinked to original sources

arXiv2026

Selective Biexciton Generation Under Energy-Time Entangled Quantum Light in Quantum Dots

Energy-time entangled photons provide new opportunities for controlling multiphoton absorption beyond classical limits. Here, we investigate biexciton generation in nanocrystal quantum dots driven by energy-time-entangled quantum light generated via a spontaneous parametric down-conversion process. We show that quantum correlations can enhance biexciton production while suppressing excitonic populations. By employing a three-level model, we demonstrate that biexciton generation depends nontrivially on the photon arrival-time entanglement and the pump bandwidth. Consequently, we find that maximizing efficiency requires an optimally shaped entangled photon field rather than simply scaling parameters for a monotonic improvement. Extending to a realistic CdSe/CdS core-shell quantum dots containing many excitonic states coupled to the quantum field, we demonstrate that increasing the bi-photon arrival time entanglement (closer arrival time) enhances constructive pathway interference and expands accessible excitation channels while preserving a better energy conservation excitation than classical light when generating biexciton. Furthermore, tuning the time correlation properties enables selective excitation of closely spaced biexciton states. These results establish entangled quantum light as a powerful tool for selective excitation and control of nonlinear optical processes in quantum-confined systems.

physics.chem-ph↗

arXiv2026

Full Quantum and Mixed Quantum--Classical Dynamics of Hot Exciton Cooling in Semiconductor Nanocrystals

Hot-exciton relaxation in semiconductor nanocrystals (NCs) is often described using perturbative theories, but their accuracy is difficult to assess for realistic exciton--phonon Hamiltonians. Here, we benchmark the perturbative quantum master equation (QME) and several mixed quantum--classical (MQC) methods against fully quantum mechanical dynamics. Using atomistically parameterized models for CdSe core and CdSe/CdS core--shell NCs, we find that bare CdSe exhibits an ultrafast initial decay followed by slower cooling, whereas the core--shell system is dominated by the slower component. Analysis of reduced models shows that the ultrafast component arises from rapid diabatic state mixing driven by thermal fluctuations of low-frequency phonons, rather than from nuclear-assisted energy relaxation. The QME captures the initial fast decay but can fail for the slower relaxation in the diabatic representation, while the mapping approach to surface hopping (MASH) gives the most consistent agreement with both benchmark dynamics and equilibrium populations. These results establish a benchmark for exciton-cooling dynamics in NCs and clarify the physical regimes in which widely used approximate methods are reliable.

physics.chem-ph↗

arXiv2026

Photoluminescence Line Shapes of Nanocrystals: Contributions from First- and Second-Order Vibronic Couplings

We present a microscopic, parameter-free approach for computing the photoluminescence spectra of a single semiconductor nanocrystal. The method derives exciton-phonon coupling directly from the semi-empirical pseudopotential framework and systematically incorporates both diagonal and off-diagonal interactions, expanded to second-order in the phonon modes. The dipole-dipole correlation function was calculated using a Dyson expansion within the Kubo-Toyozawa formalism, enabling a consistent description of the role of pure dephasing and population-transfer on the photoluminescence spectral features. Applied to CdSe/CdS core-shell nanocrystals, the approach quantitatively reproduces experimental photoluminescence spectra over a wide temperature range, revealing that quadratic phonon couplings account for nearly half of the homogeneous linewidth above 100-150 K, while off-diagonal couplings leading to exciton thermalization play only a minor role and only as T approaches 300K.

physics.chem-ph↗

arXiv2025

Deep-learning atomistic semi-empirical pseudopotential model for nanomaterials

The semi-empirical pseudopotential method (SEPM) has been widely applied to provide computational insights into the electronic structure, photophysics, and charge carrier dynamics of nanoscale materials. We present "DeepPseudopot", a machine-learned atomistic pseudopotential model that extends the SEPM framework by combining a flexible neural network representation of the local pseudopotential with parameterized non-local and spin-orbit coupling terms. Trained on bulk quasiparticle band structures and deformation potentials from GW calculations, the model captures many-body and relativistic effects with very high accuracy across diverse semiconducting materials, as illustrated for silicon and group III-V semiconductors. DeepPseudopot's accuracy, efficiency, and transferability make it well-suited for data-driven in silico design and discovery of novel optoelectronic nanomaterials.

cond-mat.mtrl-sci↗

arXiv2025

Unraveling Exciton Trap Dynamics and Nonradiative Loss Pathways in Quantum Dots via Atomistic Simulations

Surface defects in colloidal quantum dots are a major source of nonradiative losses, yet the microscopic mechanisms underlying exciton trapping and recombination remain elusive. Here, we develop a model Hamiltonian based on atomistic electronic calculations to investigate exciton dynamics in CdSe/CdS core/shell QDs containing a single hole trap introduced by an unpassivated sulfur atom. By systematically varying the defect depth and reorganization energy, we uncover how defect-induced excitonic states mediate energy relaxation pathways. Our simulations reveal that a single localized defect can induce a rich spectrum of excitonic states, leading to multiple dynamical regimes, from slow, energetically off-resonant trapping to fast, cascaded relaxation through in-gap defect states. Crucially, we quantify how defect-induced polaron shifts and exciton-phonon couplings govern the balance between efficient radiative emission and rapid nonradiative decay. These insights clarify the microscopic origin of defect-assisted loss channels and suggest pathways for tailoring QD optoelectronic properties via surface and defect engineering.

physics.chem-ph↗

arXiv2025

Compact Gaussian basis sets for stochastic DFT calculations

This work presents new Gaussian single- and double-zeta basis sets optimized for stochastic density functional theory (sDFT) using real-space auxiliary grids. Previous studies showed standard basis sets like STO-3G and 6-31G are sub-optimal for this approach. Our basis-set's Gaussian-type orbitals (GTOs) resemble norm-conserving pseudo-orbitals for H, C, N, O, F, and Si, but minimize real-space and momentum-space support. These basis sets achieve accuracy comparable to established sets while offering improved efficiency for sDFT calculations with auxiliary grids.

physics.chem-ph↗

arXiv2025

Frequency-dependent specific heat in quantum supercooled liquids: A mode-coupling study

Frequency-dependence of specific heat in supercooled hard sphere liquid is computed using quantum mode-coupling theory (QMCT). Mode-coupling equations are solved using recently proposed perturbative method that allows to study relaxation in the moderate quantum regime where quantum effects assist liquid to glass transition. Zwanzig's formulation is used to compute the frequency-dependent specific heat in supercooled state using dynamical information from QMCT. Specific heat shows strong variation as the quantumness of the liquid is changed, which becomes more significant as density is increased. It is found that, near the transition point, different dynamical modes contribute to the specific heat in the classical and the quantum liquids.

cond-mat.stat-mech↗

arXiv2025

Tagged particle dynamics in supercooled quantum liquid

We analyze dynamics of quantum supercooled liquids in terms of tagged particle dynamics. Unlike the classical case, uncertainty in the position of a particle in quantum liquid leads to qualitative changes. We demonstrate these effects in the dynamics of the first two moments of displacements, namely, the mean-squared displacement, $\langle \Delta r^2(t)\rangle$, and $\langle \Delta r^4(t)\rangle$. Results are presented for a hard sphere liquid using mode-coupling theory (MCT) formulation and simulation on a binary Lennard-Jones liquid. As the quantumness (controlled by the de-Broglie thermal wavelength) is increased, a non-zero value of the moments at zero time leads to significant deviations from the classical behavior in the initial dynamics. Initial displacement shows ballistic behavior $\langle \Delta r^2(t)\rangle\sim t^2$, but, as a result of large uncertainty in the position, the dynamical effects become weaker with increasing quantumness over this time scale.

cond-mat.stat-mech↗

arXiv2024

Revealing the phonon bottleneck limit in negatively charged CdS quantum dots

The capture of photoexcited hot electrons in semiconductors before they lose their excess energy to cooling is a long-standing goal in photon energy conversion. Semiconductor nanocrystals have large electron energy spacings that are expected to slow down electron relaxation by phonon emission, but hot electrons in photoexcited nanocrystals nevertheless cool rapidly by energy transfer to holes. This makes the intrinsic phonon-bottleneck limited electron lifetime in nanocrystals elusive. We used a combination of theory and experiments to probe the hot electron dynamics of negatively charged Cadmium Sulfide (CdS) colloidal quantum dots (QDs) in the absence of holes. Experiments found that these hot electrons cooled on a 100 ps timescale. Theoretical simulations predicted that pure phonon-bottleneck limited electron cooling occurs on a similar timescale. This similarity suggests that the experimental measurements reflect the upper limit on hot electron lifetimes in these CdS QDs and the lower limit on the rates of processes that can harvest those hot electrons.

cond-mat.mtrl-sci↗

arXiv2024

Theoretical insights into the role of lattice fluctuations on the excited behavior of lead halide perovskites

Lead halide perovskites have been extensively studied as a class of materials with unique optoelectronic properties. A fundamental aspect that governs optical and electronic behaviors within these materials is the intricate coupling between charges and their surrounding lattice. Unravelling the role of charge-lattice interactions on the optoelectronic properties in lead halide perovskites is necessary to understand their photophysics. Unlike traditional semiconductors where a harmonic approximation often suffices to capture lattice fluctuations, lead halide perovskites have a significant anharmonicity attributed from the rocking and tilting motions of inorganic framework. Thus, while there is broad consensus on the importance of the structural deformations and polar fluctuations on the behavior of charge carriers and quasiparticles, the strongly anharmonic nature of these fluctuations and their strong interactions render theoretical descriptions of lead halides perovskites challenging. In this Account, we review our recent efforts to understand how the soft, polar lattice of this class of materials alter their quasiparticle binding energies and fine structure, charge mobilities, and lifetimes of phonons and excess charges. Throughout, these are aimed at characterizing the interplay between lattice fluctuations and optoelectronic properties of lead halide perovskites and are reviewed in the context of the effective models we have built, and the novel theoretical methods we have developed to understand bulk crystalline materials, as well as nanostructures, and lower dimensionality lattices. By integrating theoretical advances with experimental observations, the perspective we detail in this account provides a comprehensive picture that serves as both design principles for optoelectronic materials and a set of theoretical tools to study them when charge-lattice interactions are important.

cond-mat.mtrl-sci↗

arXiv2024

Intrinsically slow cooling of hot electrons in CdSe nanocrystals compared to CdS

The utilization of excited charge carriers in semiconductor nanocrystals (NCs) for optoelectronic technologies has been a long-standing goal in the field of nanoscience. Experimental efforts to extend the lifetime of excited carriers have therefore been a principal focus. To understand the limits of these lifetimes, in this work, we theoretically study the timescales of pure electron relaxation in negatively charged NCs composed of two prototypical materials: CdSe and CdS. We find that hot electrons in CdSe have lifetimes that are five to six orders of magnitude longer than in CdS when the relaxation is governed only by the intrinsic properties of the materials. Although these two materials are known to have somewhat different electronic structure, we elucidate how this enormous difference in lifetimes arises from relatively small quantitative differences in electronic energy gaps, phonon frequencies, and their couplings. We also highlight that the effect of the phonons on electron relaxation is dominated by a Fr\"ohlich-type mechanism in these charged systems with no holes.

physics.chem-ph↗

arXiv2024

Non-Monotonic Size-Dependent Exciton Radiative Lifetime in CsPbBr3 Nanocrystals

Lead-halide perovskite nanocrystals have recently emerged as desirable optical materials for applications such as coherent quantum light emitters and solid-state laser cooling due to their short radiative lifetime and near-unity photoluminescence quantum yield. Here, we investigate the effect of CsPbBr3 nanocrystal size on the radiative lifetime under ambient conditions. High-quality nanocrystals, with monoexponential time-resolved photoluminescence decay behaviors, unveil a non-monotonic trend in radiative lifetime. This non-monotonicity appears to reflect a behavior common among II-VI (CdSe) and perovskites semiconducting nanocrystals. We find that large nanocrystals in the weak quantum confinement regime exhibit long radiative lifetimes due to a thermally accessible population of dim states. Small nanocrystals within the strong quantum confinement regime, surprisingly, also show long radiative lifetimes, due however to a substantial reduction in oscillator strength. Nanocrystals in the intermediate quantum confinement regime displays the shortest radiative lifetime, as their oscillator strength is enhanced relative to particles in the strong confinement regime, but do not have sufficient low-lying dim states like the large particles to counteract this affect. These findings shed light on the impact of nanocrystal size on radiative lifetime and pave the way for tailored optical materials in various optical applications.

cond-mat.mtrl-sci↗

arXiv2024

The Role of Superlattice Phonons in Charge Localization Across Quantum Dot Arrays

Understanding charge transport in semiconductor quantum dot (QD) assemblies is important for developing the next generation of solar cells and light-harvesting devices based on QD technology. One of the key factors that governs the transport in such systems is related to the hybridization between the QDs. Recent experiments have successfully synthesized QD molecules, arrays, and assemblies by directly fusing the QDs, with enhanced hybridization leading to high carrier mobilities and coherent band-like electronic transport. In this work, we theoretically investigate the electron transfer dynamics across a finite CdSe-CdS core-shell QD array, considering up to seven interconnected QDs in one dimension. We find that, even in the absence of structural and size disorder, electron transfer can become localized by the emergent low-frequency superlattice vibrational modes when the connecting neck between QDs is narrow. On the other hand, we also identify a regime where the same vibrational modes facilitate coherent electron transport when the connecting necks are wide. Overall, we elucidate the crucial effects of electronic and superlattice symmetries and their couplings when designing high-mobility devices based on QD superlattices.

physics.chem-ph↗

arXiv2024

Polariton assisted incoherent to coherent excitation energy transfer between colloidal nanocrystal quantum dots

We explore the dynamics of energy transfer between two nanocrystal quantum dots placed within an optical microcavity. By adjusting the coupling strength between the cavity photon mode and the quantum dots, we have the capacity to fine-tune the effective coupling between the donor and acceptor. Introducing a nonadiabatic parameter, $\gamma$, governed by the coupling to the cavity mode, we demonstrate the system's capability to shift from the overdamped Forster regime ($\gamma \ll 1$) to an underdamped coherent regime ($\gamma \gg 1$). In the latter regime, characterized by swift energy transfer rates, the dynamics are influenced by decoherence times. To illustrate this, we study the exciton energy transfer dynamics between two closely positioned CdSe/CdS core/shell quantum dots with sizes and separations relevant to experimental conditions. Employing an atomistic approach, we calculate the excitonic level arrangement, exciton-phonon interactions, and transition dipole moments of the quantum dots within the microcavity. These parameters are then utilized to define a model Hamiltonian. Subsequently, we apply a generalized non-Markovian quantum Redfield equation to delineate the dynamics within the polaritonic framework.

cond-mat.mes-hall↗

arXiv2024

Convergence Analysis of the Stochastic Resolution of Identity: Comparing Hutchinson to Hutch++ for the Second-Order Green's Function

Stochastic orbital techniques offer reduced computational scaling and memory requirements to describe ground and excited states at the cost of introducing controlled statistical errors. Such techniques often rely on two basic operations, stochastic trace estimation and stochastic resolution of identity, both of which lead to statistical errors that scale with the number of stochastic realizations ($N_{\xi}$) as $\sqrt{N_{\xi}^{-1}}$. Reducing the statistical errors without significantly increasing $N_{\xi}$ has been challenging and is central to the development of efficient and accurate stochastic algorithms. In this work, we build upon recent progress made to improve stochastic trace estimation based on the ubiquitous Hutchinson's algorithm and propose a two-step approach for the stochastic resolution of identity, in the spirit of the Hutch++ method. Our approach is based on employing a randomized low-rank approximation followed by a residual calculation, resulting in statistical errors that scale much better than $\sqrt{N_{\xi}^{-1}}$. We implement the approach within the second-order Born approximation for the self-energy in the computation of neutral excitations and discuss three different low-rank approximations for the two-body Coulomb integrals. Tests on a series of hydrogen dimer chains with varying lengths demonstrate that the Hutch++-like approximations are computationally more efficient than both deterministic and purely stochastic (Hutchinson) approaches for low error thresholds and intermediate system sizes. Notably, for arbitrarily large systems, the Hutchinson-like approximation outperforms both deterministic and Hutch++-like methods.

physics.chem-ph↗

arXiv2024

Ligand Induced Size-Dependent Circular Dichroism in Quantum Dots

Recent experiments have probed the chiral properties of semiconductor nanocrystal (NC) quantum dots (QDs), but understanding the circular dichroism lineshape, excitonic features, and ligand induction mechanism remains a challenge. We propose an atomistic pseudopotential method to model chiral ligand passivated QDs, computing circular dichroism (CD) spectra for CdSe QDs (2.6 - 3.8 nm). We find strong agreement between calculated and measured spectra, predicting consistent bisignate lineshapes with decreasing CD magnitude as size increases. Our analysis reveals the origin of bisignate lineshapes, arising from nondegenerate excitons with opposing angular momenta. We also explore the impact of chiral ligand orientation on QD surfaces, observing changes in optical activity magnitude and sign. This orientation sensitivity offers means to distinguish ordered from disordered ligand configurations, facilitating the study of order-disorder transitions at ligand-QD interfaces.

cond-mat.mtrl-sci↗

arXiv2024

Stochastic density functional theory combined with Langevin dynamics for warm dense matter

This study overviews and extends a recently developed stochastic finite-temperature Kohn-Sham density functional theory to study warm dense matter using Langevin dynamics, specifically under periodic boundary conditions. The method's algorithmic complexity exhibits nearly linear scaling with system size and is inversely proportional to the temperature. Additionally, a novel linear-scaling stochastic approach is introduced to assess the Kubo-Greenwood conductivity, demonstrating exceptional stability for DC conductivity. Utilizing the developed tools, we investigate the equation of state, radial distribution, and electronic conductivity of Hydrogen at a temperature of 30,000K. As for the radial distribution functions, we reveal a transition of Hydrogen from gas-like to liquid-like behavior as its density exceeds $4 g/cm^3$. As for the electronic conductivity as a function of the density, we identified a remarkable isosbestic point at frequencies around 7eV, which may be an additional signature of a gas-liquid transition in Hydrogen at 30,000K.

cond-mat.mtrl-sci↗

arXiv2024

Simple Diagonal State Designs with Reconfigurable Real-Time Circuits

Unitary designs are widely used in quantum computation, but in many practical settings it suffices to construct a diagonal state design generated with unitary gates diagonal in the computational basis. In this work, we introduce a simple and efficient diagonal state 3-design based on real-time evolutions under 2-local Hamiltonians. Our construction is inspired by the classical Girard-Hutchinson trace estimator in that it involves the stochastic preparation of many random-phase states. Though the exact Girard-Hutchinson states are not tractably implementable on a quantum computer, we can construct states that match the statistical moments of the Girard-Hutchinson states with real-time evolution. Importantly, our random states are all generated using the same Hamiltonians for real-time evolution, with the randomness arising solely from stochastic variations in the durations of the evolutions. In this sense, the circuit is fully reconfigurable and thus suited for near-term realizations on both digital and analog platforms. Moreover, we show how to extend our construction to achieve diagonal state designs of arbitrarily high order.

quant-ph↗