arXiv subjects

Hendrik Utzat

Publications and source records attributed to Hendrik Utzat.

14 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

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

Heralded Emission Detection in InAs/ZnSe Quantum Dot Solids Using Time-Correlated Photons

Harnessing quantum correlations between photons is an emerging frontier in optical spectroscopy, yet experimental demonstrations have largely remained limited to molecular systems at room temperature. Here, we investigate heralded emission detection (HED) under continuous-wave entangled-photon excitation of near-infrared (NIR)-emitting colloidal III-V quantum dot (QD) solids at low temperatures. We demonstrate the advantages of superconducting nanowire single-photon detectors (SNSPDs) for high time resolution ($\sim$72 ps) and large-area NIR avalanche photodiodes (APDs) for high emission count rates ($\sim$2000 cps). Second-order photon-correlation analysis reveals exciton lifetimes and fine-structure energy splittings. These results establish NIR colloidal QDs as a bright, tunable model system for quantum-light spectroscopy and highlight their compatibility with optical cavities as a further experimental control parameter.

physics.optics↗

arXiv2025

Multi-Dimensional Photon-Correlations Reveal Triexciton Features in Single Perovskite Quantum Dots

Lead-halide perovskite quantum dots (PQDs) are established quantum emitters with potential for entangled photon-pair generation via multiexciton cascades. However, the energetics and dynamics of many-body excitations remain poorly understood. Here, we perform time- and frequency-resolved photon-correlation spectroscopy of single CsPbBr\textsubscript{3} PQDs at low temperatures using a single-photon avalanche diode (SPAD) array detector. We report biexciton binding energies and assign their charged states, which undergo fast ($μ$s) switching dynamics. Most notably, we identify a spectral feature blue-shifted from the exciton by $7.4 \pm 1.9$ meV as the bound triexciton and establish the order of its cascade emission. These results highlight the power of low-temperature, multidimensional photon-correlation spectroscopy for resolving complex many-body dynamics.

cond-mat.mtrl-sci↗

arXiv2025

Enhancing Spectroscopy and Microscopy with Emerging Methods in Photon-Correlation and Quantum Illumination

Quantum optics has driven major advances in our ability to generate and detect correlations between individual photons. Its principles are now increasingly translated into nanoscale characterization techniques, enhancing spectroscopy, microscopy, and metrology. In this Review, we highlight rapid progress in the field driven by advances in single-photon detectors and quantum light sources, including time-resolved single-photon counting cameras, superconducting nanowire detectors, and increasingly bright sources of entangled photons. We emphasize emerging applications in super-resolution microscopy, measurements below classical noise limits, and photon-number-resolved spectroscopy-a powerful paradigm for probing nanoscale electronic materials and molecular dynamics. We conclude by outlining key technological challenges and future opportunities across materials science and bio-nanophotonics.

physics.optics↗

arXiv2025

Stochastic Equilibrium Raman Spectroscopy (STERS)

We theoretically propose a new method in cavity- and surface-enhanced Raman spectroscopy (SERS) with improved temporal resolution in the measurement of stochastic Raman spectral fluctuations. Our approach combines Fourier spectroscopy and photon correlation to decouple the integration time from the temporal resolution. Using statistical optics simulations, we establish the relationship between time resolution and Raman signal strength, revealing that typical Raman spectral fluctuations, commensurate with molecular conformational dynamics, can theoretically be resolved on micro- to millisecond timescales. The method can further extract average single-molecule dynamics from small sub-ensembles, thereby potentially mitigating challenges in achieving strictly single-molecule isolation on SERS substrates.

physics.optics↗

arXiv2024

Stochastic Frequency Fluctuation Super-Resolution Imaging

The inherent non-linearity of intensity correlation functions can be used to spatially distinguish identical emitters beyond the diffraction limit, as achieved, for example, in Super-Resolution Optical Fluctuation Imaging (SOFI). Here, we propose a complementary concept based on spectral correlation functions, termed Spectral Fluctuation Super-Resolution (SFSR) imaging. Through theoretical and computational analysis, we show that spatially resolving time-frequency correlation functions in the image plane can improve the imaging resolution by a factor of $\sqrt2$ in most cases and up to twofold for strictly two emitters. This improvement is achieved by quantifying the degree of correlation in spectral fluctuations across the spatial domain. Experimentally, SFSR can be implemented using a combination of interferometry and photon-correlation measurements. The method works for non-blinking emitters and stochastic spectral fluctuations with arbitrary temporal statistics. This suggests its utility in super-resolution microscopy of quantum emitters at low temperatures, where spectral diffusion is often more pronounced than emitter blinking.

physics.optics↗

arXiv2022

Accelerating quantum materials development with advances in transmission electron microscopy

Quantum materials are driving a technology revolution in sensing, communication, and computing, while simultaneously testing many core theories of the past century. Materials such as topological insulators, complex oxides, quantum dots, color center hosting semiconductors, and other types of strongly correlated materials can exhibit exotic properties such as edge conductivity, multiferroicity, magnetoresistance, single photon emission, and optical-spin locking. These emergent properties arise and depend strongly on the materials detailed atomic scale structure, including atomic defects, dopants, and lattice stacking. In this review, after introduction of different classes of quantum materials and quantum excitations, we describe how progress in the field of electron microscopy, including in situ and in operando EM, can accelerate advances in quantum materials. Our review describes EM methods including: i) principles and operation modes of EM, ii) EM spectroscopies, such as electron energy loss spectroscopy, cathodoluminescence, and electron energy gain spectroscopy, iii) 4D scanning transmission electron microscopy, iv) dynamic and ultrafast EM, v) complimentary ultrafast spectroscopies, and vi) atomic electron tomography. We discuss how these methods inform structure function relations in quantum materials down to the picometer scale and femtosecond time resolution, and how they enable high resolution manipulation of quantum materials. Among numerous results, our review highlights how EM has enabled identification of the 3D structure of quantum defects, measuring reversible and metastable dynamics of quantum excitations, mapping exciton states and single photon emission, measuring nanoscale thermal transport and coupled excitation dynamics, and measuring the internal electric field of quantum heterointerfaces, all at the quantum materials intrinsic atomic and near atomic-length scale.

cond-mat.mtrl-sci↗

arXiv2022

Theory of photoluminescence spectral line shapes of semiconductor nanocrystals

Single-molecule photoluminescence (PL) spectroscopy of semiconductor nanocrystals (NCs) reveals the nature of exciton-phonon interactions in NCs. Understanding the narrow line shapes at low temperatures and the significant broadening as temperature increases remains an open problem. Here, we develop an atomistic model to describe the PL spectrum of NCs, accounting for excitonic effects, phonon dispersion relations, and exciton-phonon couplings. We use single-molecule PL measurements on CdSe/CdS core-shell NCs from T=4 to T=290K to validate our model and find that the slightly-asymmetric main peak at low temperatures is comprised of a narrow zero-phonon line (ZPL) and several acoustic phonon sidebands. Furthermore, we identify the distinct CdSe optical modes that give rise to the optical phonon sidebands. As the temperature increases, the spectral width shows a stronger dependence on temperature, which we demonstrated to be correlated with frequency shifts and mode-mixing, reflected as higher-order exciton-phonon couplings (Duschinsky rotations). We also model the PL dependence on core size and shell thickness and provide strategies for the design of NCs with narrow linewidths at elevated temperatures.

cond-mat.mes-hall↗

arXiv2022

Nanodiamond grain boundaries and lattice expansion drive Silicon vacancy emission heterogeneity

Silicon-vacancy (SiV$^-$) centers in diamond are promising candidates as sources of single-photons in quantum networks due to their minimal phonon coupling and narrow optical linewidths. Correlating SiV$^-$ emission with the defect's atomic-scale structure is important for controlling and optimizing quantum emission, but remains an outstanding challenge. Here, we use cathodoluminescence imaging in a scanning transmission electron microscope (STEM) to elucidate the structural sources of non-ideality in the SiV$^-$ emission from nanodiamonds with sub-nanometer-scale resolution. We show that different crystalline domains of a nanodiamond exhibit distinct zero-phonon line (ZPL) energies and differences in brightness, while near-surface SiV$^-$ emitters remain bright. We correlate these changes with local lattice expansion using 4D STEM and diffraction, and show that associated blue shifts from the ZPL are due to defect density heterogeneity, while red shifts are due to lattice distortions.

physics.app-ph↗

arXiv2021

Terahertz Field-Induced Reemergence of Quenched Photoluminescence in Quantum Dots

Continuous and concerted development of colloidal quantum-dot light-emitting diodes over the past two decades has established them as a bedrock technology for the next generation of displays. However, a fundamental issue that limits the performance of these devices is the quenching of photoluminescence due to excess charges from conductive charge transport layers. Although device designs have leveraged various workarounds, doing so often comes at the cost of limiting efficient charge injection. Here we demonstrate that high-field terahertz (THz) pulses can dramatically brighten quenched QDs on metallic surfaces, an effect which persists for minutes after THz irradiation. This phenomenon is attributed to the ability of the THz field to remove excess charges, thereby reducing trion and non-radiative Auger recombination. Our findings show that THz technologies can be used to suppress and control such undesired non-radiative decay, potentially in a variety of luminescent materials for future device applications.

cond-mat.mes-hall↗

arXiv2021

All-optical fluorescence blinking control in quantum dots with ultrafast mid-infrared pulses

Photoluminescence (PL) intermittency is a ubiquitous phenomenon detrimentally reducing the temporal emission intensity stability of single colloidal quantum dots (CQDs) and the emission quantum yield of their ensembles. Despite efforts for blinking reduction via chemical engineering of the QD architecture and its environment, blinking still poses barriers to the application of QDs, particularly in single-particle tracking in biology or in single-photon sources. Here, we demonstrate the first deterministic all-optical suppression of quantum dot blinking using a compound technique of visible and mid-infrared (MIR) excitation. We show that moderate-field ultrafast MIR pulses (5.5 $μ$m, 150 fs) can switch the emission from a charged, low quantum yield 'grey' trion state to the 'bright' exciton state in CdSe/CdS core-shell quantum dots resulting in a significant reduction of the QD intensity flicker. Quantum-tunneling simulations suggest that the MIR fields remove the excess charge from trions with reduced emission quantum yield to restore higher brightness exciton emission. Our approach can be integrated with existing single-particle tracking or super-resolution microscopy techniques without any modification to the sample and translates to other emitters presenting charging-induced PL intermittencies, such as single-photon emissive defects in diamond and two-dimensional materials.

cond-mat.mes-hall↗

arXiv2021

Lifetime-resolved Photon-Correlation Fourier Spectroscopy

The excited state population of single solid-state emitters is subjected to energy fluctuations around the equilibrium driven by the bath and relaxation through the emission of phonons or photons. Simultaneous measurement of the associated spectral dynamics requires a technique with a high spectral and temporal resolution with an additionally high temporal dynamic range. We propose a pulsed excitation-laser analog of Photon-Correlation Fourier Spectroscopy (PCFS), which extracts the lineshape and spectral diffusion dynamics along the emission lifetime trajectory of the emitter, effectively discriminating spectral dynamics from relaxation and bath fluctuations. This lifetime-resolved PCFS correlates photon-pairs at the output arm of a Michelson interferometer in both their time-delay between laser-excitation and photon-detection and the time-delay between two photons. We propose the utility of the technique for systems with changing relative contributions to the emission from multiple states, for example, quantum emitters exhibiting phonon-mediated exchange between different fine-structure states.

quant-ph↗

arXiv2018

Coherent Single Photon Emission from Colloidal Lead Halide Perovskite Quantum Dots

Chemically prepared colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single photon emission with optical coherence times as long as 80 ps, an appreciable fraction of their 210 ps radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Our results present a starting point for the rational design of lead halide perovskite-based quantum emitters with fast emission, wide spectral-tunability, scalable production, and which benefit from the hybrid-integration with nano-photonic components that has been demonstrated for colloidal materials.

cond-mat.mes-hall↗