arXiv subjects

Wojciech Rudno-Rudziński

Publications and source records attributed to Wojciech Rudno-Rudziński.

8 recordsLinked to original sources

arXiv2026

Emission dynamics in zincblende InAsxP1-x quantum dots in InP nanowires: influence of quantum dot size, composition and nanowire geometry

Hereby, we present an experimental and theoretical investigation of emission dynamics in zincblende InAsxP1-x quantum dots (QDs) embedded in InP nanowires (NWs) grown via vapour-liquid-solid mechanism by chemical beam epitaxy, using Au nanoparticles as a nucleation catalyst. By measuring time-resolved photoluminescence from an ensemble of QD-NWs it was possible to determine the exciton lifetime dependence on QD composition and height. Changes in the InP shell thickness surrounding the InP NW stem with a QD, brought additional insight into the influence of photonic environment on the carrier dynamics. High-resolution transmission electron microscopy, combined with energy-dispersive X-ray spectroscopy, provided actual structural parameters. The experimentally obtained lifetimes were interpreted in the light of results of 8 band kp calculations combined with configuration-interaction model to take into account the Coulomb interactions and finite-difference time domain photonic simulations to include the effect of optical confinement. The full understanding of the experimental results required considering both, the changes in the QD potential and the Purcell effect, the latter leading to spontaneous emission inhibition in the case of NWs with thin InP shell.

cond-mat.mes-hall↗

arXiv2026

Two-photon interference from as-grown InAsP/InP quantum dots under detuned excitation

In this study, we investigate as-grown InAsP/InP quantum dots emitting in the third telecommunication window under detuned quasi-resonant excitation. A large excitation-emission detuning of 32 meV enables efficient suppression of scattered laser light while retaining several advantages of near-resonant excitation. The single-photon nature of the emission is confirmed by a Hanbury Brown and Twiss experiment, yielding a raw second-order autocorrelation value of $g_{\mathrm{raw}}^{(2)}(0)=0.076(6)$. Hong-Ou-Mandel measurement is used to determine the degree of indistinguishability of single photons and reveal as measured visibilities of $V=0.094(4)$ and $V=0.106(5)$ for excitation pulse separations of 13.1 ns and 5.3 ns, respectively. These results demonstrate the potential of as-grown InAsP/InP quantum dots grown via molecular beam epitaxy under not experimentally demanding detuned excitation for generating indistinguishable telecom single photons. Further improvements are to be achieved through Purcell enhancement in optical cavities.

quant-ph↗

arXiv2025

Probing electron spin dynamics in single telecom InAs(P)/InP quantum dots using the Hanle effect

Spins of carriers confined in quantum dots (QDs) are promising candidates for qubits due to their relatively long spin relaxation times. However, the electron spin dephasing, primarily driven by hyperfine interactions with nuclear spins, can limit their coherence. Here, we report the first Hanle effect demonstration in single InAs(P)/InP QDs emitting in the telecom C-band leading to experimental determination of electron spin dephasing time. Using polarization-resolved photoluminescence spectroscopy, we identified excitonic complexes and confirmed the presence of a negatively charged trion, exhibiting a degree of circular polarization (DOCP) of $-36\%$ under quasi--resonant excitation. From the analysis of Hanle linewidth and employing a previously reported value of the electron $g$-factor, we extracted an electron spin dephasing time of $T_2^{\ast} = 1.59 \pm 0.49~\mathrm{ns}$. Despite the large indium nuclear spin, the obtained $T_2^{\ast}$ is comparable to values reported for GaAs-based QDs, which we attribute to the larger volume of the InAs(P)/InP QDs. These findings confirm the potential of InP-based telecom QDs for use in spin-photon interfaces.

cond-mat.mes-hall↗

arXiv2025

Generation of C-band entangled photon pairs by biexciton-exciton cascade from symmetric InAs/InP quantum dots

Hereby, we study the generation of pairs of polarization-entangled photons at telecom C-band by biexciton-exciton cascade from non-resonantly excited epitaxial InAs/InP quantum dots (QDs). It is realized without external tuning of the fine structure splitting (FSS), which does not exceed 10 $μ$eV in as-grown nanostructures, due to their high in-plane symmetry. Excitonic complexes are identified by means of excitation power-dependent and polarization-resolved magneto)microphotoluminescence. Their origin from different carrier configurations confined in the same QD is confirmed by time correlations of emitted photons. Experimental results are supported by 8-band kp calculations, followed by the configuration interaction method to include excitonic effects. This comparison reveals the structure of higher energy states, allowing for the reconstruction of the QD structural parameters. To verify and quantify the entanglement, we perform quantum state tomography and reconstruct the two-photon density matrix. Its diagonalization allows a detailed analysis of the entangled state and reveals an unfavourable interplay between phase accumulation and decoherence, pointing to a clear route for boosting entanglement by using a XX resonant, pulsed excitation scheme and shortening the radiative lifetimes.

quant-ph↗

arXiv2024

Transfer Learning and the Early Estimation of Single-Photon Source Quality using Machine Learning Methods

The use of single-photon sources (SPSs) is central to numerous systems and devices proposed amidst a modern surge in quantum technology. However, manufacturing schemes remain imperfect, and single-photon emission purity must often be experimentally verified via interferometry. Such a process is typically slow and costly, which has motivated growing research into whether SPS quality can be more rapidly inferred from incomplete emission statistics. Hence, this study is a sequel to previous work that demonstrated significant uncertainty in the standard method of quality estimation, i.e. the least-squares fitting of a physically motivated function, and asks: can machine learning (ML) do better? The study leverages eight datasets obtained from measurements involving an exemplary quantum emitter, i.e. a single InGaAs/GaAs epitaxial quantum dot; these eight contexts predominantly vary in the intensity of the exciting laser. Specifically, via a form of `transfer learning', five ML models, three linear and two ensemble-based, are trained on data from seven of the contexts and tested on the eighth. Validation metrics quickly reveal that even a linear regressor can outperform standard fitting when it is tested on the same contexts it was trained on, but the success of transfer learning is less assured, even though statistical analysis, made possible by data augmentation, suggests its superiority as an early estimator. Accordingly, the study concludes by discussing future strategies for grappling with the problem of SPS context dissimilarity, e.g. feature engineering and model adaptation.

physics.optics↗

arXiv2024

Effects of dislocation filtering layers on optical properties of third telecom window emitting InAs/InGaAlAs quantum dots grown on silicon substrates

Integrating light emitters based on III-V materials with silicon-based electronics is crucial for further increase in data transfer rates in communication systems since the indirect bandgap of silicon prevents its direct use as a light source. We investigate here InAs/InGaAlAs quantum dot (QD) structures grown directly on 5° off-cut Si substrate and emitting light at 1.5 micrometers, compatible with established telecom platform. Using different dislocation defects filtering layers, exploiting strained superlattices and supplementary QD layers, we mitigate the effects of lattice constant and thermal expansion mismatches between III-V materials and Si during growth. Complementary optical spectroscopy techniques, i.e. photoreflectance and temperature-, time- and polarization- resolved photoluminescence, allow us to determine the optical quality and application potential of the obtained structures by comparing them to a reference sample -- state-of-the-art QDs grown on InP. Experimental findings are supported by calculations of excitonic states and optical transitions by combining multiband k.p and configuration-interaction methods. We show that our design of structures prevents the generation of a considerable density of defects, as intended. The emission of Si-based structures appears to be much broader than for the reference dots, due to the creation of different QD populations which might be a disadvantage in particular laser applications, however, could be favourable for others, e.g. in broadly tunable devices, sensors, or optical amplifiers. Eventually, we identify the overall most promising combination of defect filtering layers, discuss its advantages and limitations, and prospects for further improvements.

cond-mat.mes-hall↗

arXiv2024

Harnessing Data Augmentation to Quantify Uncertainty in the Early Estimation of Single-Photon Source Quality

Novel methods for rapidly estimating single-photon source (SPS) quality have been promoted in recent literature to address the expensive and time-consuming nature of experimental validation via intensity interferometry. However, the frequent lack of uncertainty discussions and reproducible details raises concerns about their reliability. This study investigates the use of data augmentation, a machine learning technique, to supplement experimental data with bootstrapped samples and quantify the uncertainty of such estimates. Eight datasets obtained from measurements involving a single InGaAs/GaAs epitaxial quantum dot serve as a proof-of-principle example. Analysis of one of the SPS quality metrics derived from efficient histogram fitting of the synthetic samples, i.e. the probability of multi-photon emission events, reveals significant uncertainty contributed by stochastic variability in the Poisson processes that describe detection rates. Ignoring this source of error risks severe overconfidence in both early quality estimates and claims for state-of-the-art SPS devices. Additionally, this study finds that standard least-squares fitting is comparable to using a Poisson likelihood, and expanding averages show some promise for early estimation. Also, reducing background counts improves fitting accuracy but does not address the Poisson-process variability. Ultimately, data augmentation demonstrates its value in supplementing physical experiments; its benefit here is to emphasise the need for a cautious assessment of SPS quality.

physics.optics↗

arXiv2021

Magneto-optical characterization of trions in symmetric InP-based quantum dots for quantum communication applications

Magneto-optical parameters of trions in novel large and symmetric InP-based quantum dots, uncommon for molecular beam epitaxy grown nanostructures, with emission in the third telecom window, are measured in Voigt and Faraday configurations of external magnetic field. The diamagnetic coefficients are found to be in the range of 1.5-4 μeV/{\T^2}, and 8-15 μeV/{\T^2}, respectively out of plane and in plane of the dots. The determined values of diamagnetic shifts are related to the anisotropy of dot sizes. Trion g-factors are measured to be relatively small, in the range of 0.3-0.7 and 0.5-1.3, in both configurations respectively. Analysis of single carrier g-factors, based on the formalism of spin-correlated orbital currents, leads to the similar values for hole and electron of {\sim} 0.25 for Voigt and {\g_e} {\approx} -5; {\g_h} {\approx} +6 for Faraday configuration of magnetic field. Values of g-factors close to zero measured in Voigt configuration make the investigated dots promising for electrical tuning of g-factor sign, required for schemes of single spin control in qubit applications.

cond-mat.mes-hall↗