arXiv subjects

Anna Musiał

Publications and source records attributed to Anna Musiał.

At least 19 recordsLinked to original sources

arXiv2026

Temperature Dependence of the Refractive Index for AlAsGaSb

Accurate design and optimization of photonic multilayer structures like distributed Bragg reflectors (DBRs) require precise knowledge of material optical constants, particularly the temperature dependence of the refractive index. While these parameters are well established for widely used semiconductors, for emerging materials such as antimonides they are often limited to room-temperature data, especially for new spectral ranges of interest. Antimonide compounds, in particular GaSb-based alloys, are promising for quantum photonics applications. In this work, we investigated DBRs lattice-matched to GaSb and designed for operation in the third telecommunication window. Reflectivity spectra were measured in the temperature range from 11.5 K to 300 K, and then fitted using the transfer matrix method (TMM), combined with a dedicated recursive numerical fitting algorithm. Initial parameters included layer thicknesses determined by scanning electron microscopy (SEM) and literature values of refractive indices at room temperature. This approach enabled extraction of the temperature-dependent refractive indices of two AlGaAsSb alloys suitable for forming DBR mirrors for 1.5 um wavelengths. The obtained results provide essential input for reliable DBR design, ensuring proper stopband positioning and high reflectivity under cryogenic operating conditions required for efficient quantum emitter performance.

cond-mat.other↗

arXiv2026

Predictive wavelength tailoring of uniform GaSb-based quantum dots for emission at 1.55 um

A detailed study of emission wavelength tailoring of GaSb-based QDs formed by InGaSb-filling of droplet-etched nanoholes in AlGaSb is presented. The study shows that the emission wavelength can be modified from 1.48 um to the center of the telecom C-band at 1.55 mm by independently varying the QD composition and size. More specifically, the optical transition energy shifts linearly as a function of In-content of the QD material at a rate of -4.4 meV/In-percentage, and with the number of monolayers (ML) of material used for filling the nanoholes, at -2.0 meV/ML. These experimentally observed energy shifts are well predicted by simulations yielding rates of -4.3 meV/In-percentage and -2.1 meV/ML, respectively. For the simulation, a uniform In composition, low intermixing, and microscopically measured QD geometry is considered. Additionally, excellent ensemble QD uniformity, with unprecedented inhomogeneous broadening well-below 7 meV across all samples is demonstrated. Finally, photoluminescence of single-QDs reveals narrow excitonic emission lines of 13.8+/-6.7 ueV and low fine-structure splitting values reaching <10 ueV. These results identify GaSb-based LDE QDs as a tunable telecom platform for scaling quantum-photonic applications over long-haul optical fiber networks.

cond-mat.mes-hall↗

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↗

arXiv2026

A Fiber-pigtailed Quantum Dot Device Generating Indistinguishable Photons at GHz Clock-rates

Solid-state quantum light sources based on semiconductor quantum dots (QDs) are increasingly employed in photonic quantum information applications. Especially when moving towards real-world scenarios outside shielded lab environments, the efficient and robust coupling of nanophotonic devices to single-mode optical fibers offers substantial advantage by enabling "plug-and-play" operation. In this work we present a fiber-pigtailed cavity-enhanced source of flying qubits emitting single indistinguishable photons at clock-rates exceeding $1\,$GHz. This is achieved by employing a fully deterministic technique for fiber-pigtailing optimized QD-devices based on hybrid circular Bragg grating (hCBG) micro-cavities. The fabricated fiber-pigtailed hCBGs feature radiative emission lifetimes of $<80\,$ps, corresponding to a Purcell factor of $\sim$9, a suppression of multi-photon emission events with $g^{(2)}(0)<1\%$, a photon-indistinguishability $>80\%$ and a measured single-photon coupling efficiency of 53$\%$ in a high numerical aperture single-mode fiber, corresponding to 1.2 Megaclicks per second at the single-photon detectors under $80\,$MHz excitation clock-rates. Furthermore, we show that high multi-photon suppression and indistinguishability prevail for excitation clock-rates exceeding $1\,$GHz. Our results show that Purcell-enhanced fiber-pigtailed quantum light sources based on hCBG cavities are a prime candidate for applications of quantum information science.

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↗

arXiv2025

High-reflectivity homoepitaxial distributed Bragg reflectors for photonic applications

Distributed Bragg reflectors (DBRs) are one of the basic photonic structures used to define microcavities for fundamental light-matter coupling studies, as well as to optimize performance of optoelectronic and photonic devices, e.g., lasers or non-classical light sources. The reflectivity of these structures depends critically on the refractive index contrast between the two quarter-wavelength thick layers constituting the DBR. At the same time, epitaxial fabrication process limits the choice of materials to those with the same, or very similar lattice constant to avoid strain accumulation in the relatively thick multilayer structure. This becomes very often a bottleneck for the DBR designs at certain wavelengths or for some of the material systems. Therefore, we explore theoretically DBR designs employing the reflective index contrast between undoped and doped layers of the same material, making the entire growth process homoepitaxial. The refractive index for a doped layer is calculated taking into account the free carrier absorption, carrier-carrier interaction, the Burnstein-Moss and plasma effects. The reflectivity spectrum of a DBR is further calculated using transfer matrix method. Exemplary results for three application relevant materials - hBN, InP and Si suitable for different spectral ranges, i.e. ultraviolet, telecommunication and mid-infrared, respectively, are presented. We report reflectivities on the level of 90\% for technologically achievable doping concentrations and moderate number of layer pairs.

cond-mat.other↗

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

High-throughput quantum photonic devices emitting indistinguishable photons in the telecom C-band

Single indistinguishable photons at telecom C-band wavelengths are essential for quantum networks and the future quantum internet. However, high-throughput technology for single-photon generation at 1550 nm remained a missing building block to overcome present limitations in quantum communication and information technologies. Here, we demonstrate the high-throughput fabrication of quantum-photonic integrated devices operating at C-band wavelengths based on epitaxial semiconductor quantum dots. Our technique enables the deterministic integration of single pre-selected quantum emitters into microcavities based on circular Bragg gratings. Respective devices feature the triggered generation of single photons with ultra-high purity and record-high photon indistinguishability. Further improvements in yield and coherence properties will pave the way for implementing single-photon non-linear devices and advanced quantum networks at telecom wavelengths.

quant-ph↗

arXiv2024

On-Demand Generation of Indistinguishable Photons in the Telecom C-Band using Quantum Dot Devices

Semiconductor quantum dots (QDs) enable the generation of single and entangled photons, useful for various applications in photonic quantum technologies. Specifically for quantum communication via fiber-optical networks, operation in the telecom C-band centered around 1550$\,$nm is ideal. The direct generation of QD-photons in this spectral range and with high quantum-optical quality, however, remained challenging. Here, we demonstrate the coherent on-demand generation of indistinguishable photons in the telecom C-band from single QD devices consisting of InAs/InP QD-mesa structures heterogeneously integrated with a metallic reflector on a silicon wafer. Using pulsed two-photon resonant excitation of the biexciton-exciton radiative cascade, we observe Rabi rotations up to pulse areas of $4π$ and a high single-photon purity in terms of $g^{(2)}(0)=0.005(1)$ and $0.015(1)$ for exciton and biexciton photons, respectively. Applying two independent experimental methods, based on fitting Rabi rotations in the emission intensity and performing photon cross-correlation measurements, we consistently obtain preparation fidelities at the $π$-pulse exceeding 80$\%$. Finally, performing Hong-Ou-Mandel-type two-photon interference experiments we obtain a photon-indistinguishability of the full photon wave packet of up to $35(3)\%$, representing a significant advancement in the photon-indistinguishability of single photons emitted directly in the telecom C-band.

quant-ph↗

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↗

arXiv2023

Heterogeneous integration of single InAs/InP quantum dots with the SOI chip using direct bonding

Quantum information processing with photons in small-footprint and highly integrated silicon-based photonic chips requires incorporating non-classical light sources. In this respect, self-assembled III-V semiconductor quantum dots (QDs) are an attractive solution, however, they must be combined with the silicon platform. Here, by utilizing the large-area direct bonding technique, we demonstrate the hybridization of InP and SOI chips, which allows for coupling single photons to the SOI chip interior, offering cost-effective scalability in setting up a multi-source environment for quantum photonic chips. We fabricate devices consisting of self-assembled InAs QDs embedded in the tapered InP waveguide (WG) positioned over the SOI-defined Si WG. Focusing on devices generating light in the telecom C-band compatible with the low-loss optical fiber networks, we demonstrate the light coupling between InP and SOI platforms by observing photons outcoupled at the InP-made circular Bragg grating outcoupler fabricated at the end of an 80 $μ$m-long Si WG, and at the cleaved edge of the Si WG. Finally, for a device with suppressed multi-photon generation events exhibiting 80% single photon generation purity, we measure the photon number outcoupled at the cleaved facet of the Si WG. We estimate the directional on-chip photon coupling between the source and the Si WG to 5.1%.

physics.optics↗

arXiv2023

Optical characteristics of cavity structures with Al0.2Ga0.8As/Al0.9Ga0.1As distributed Bragg reflectors and In0.37Ga0.63As quantum dots as the active region

We characterized optically In0.37Ga0.63As/GaAs quantum dots and Al0.2Ga0.8As/Al0.9Ga0.1As distributed Bragg reflector based cavities. The main mechanisms of quantum dots photoluminescence quenching were identified. We measured reflectivity spectra of the cavity structure which allowed us to verify the proposed layer design and its fabrication by comparing them with the results of simulations within the transfer matrix method.

physics.app-ph↗

arXiv2022

A Quantum Key Distribution Testbed using a Plug&Play Telecom-wavelength Single-Photon Source

Deterministic solid-state quantum light sources are considered key building blocks for future communication networks. While several proof-of-principle experiments of quantum communication using such sources have been realized, most of them required large setups often involving liquid helium infrastructure or bulky closed-cycle cryotechnology. In this work, we report on the first quantum key distribution (QKD) testbed using a compact benchtop quantum dot single-photon source operating at telecom wavelengths. The plug\&play device emits single-photon pulses at O-band wavelengths ($1321\,$nm) and is based on a directly fiber-pigtailed deterministically-fabricated quantum dot device integrated into a compact Stirling cryocooler. The Stirling is housed in a 19-inch rack module including all accessories required for stand-alone operation. Implemented in a simple QKD testbed emulating the BB84 protocol with polarization coding, we achieve an antibunching of $g^{(2)}(0) = 0.10\pm0.01$ and a raw key rate of up to $(4.72\pm0.13)\,$kHz using an external pump laser. In this setting, we further evaluate the performance of our source in terms of the quantum bit error ratios, secure key rates, and tolerable losses expected in full implementations of QKD also accounting for finite key size effects. Furthermore, we investigate optimal settings for a two-dimensional temporal acceptance window applied on receiver side, resulting in predicted tolerable losses up to $23.19\,$dB. Not least, we compare our results with previous proof-of-concept QKD experiments using quantum dot single-photon sources. Our study represents an important step forward in the development of fiber-based quantum-secured communication networks exploiting sub-Poissonian quantum light sources.

quant-ph↗

arXiv2021

Bright Quantum Dot Single-Photon Emitters at Telecom Bands Heterogeneously Integrated on Si

Whereas the Si photonic platform is highly attractive for scalable optical quantum information processing, it lacks practical solutions for efficient photon generation. Self-assembled semiconductor quantum dots (QDs) efficiently emitting photons in the telecom bands ($1460-1625$ nm) allow for heterogeneous integration with Si. In this work, we report on a novel, robust, and industry-compatible approach for achieving single-photon emission from InAs/InP QDs heterogeneously integrated with a Si substrate. As a proof of concept, we demonstrate a simple vertical emitting device, employing a metallic mirror beneath the QD emitter, and experimentally obtained photon extraction efficiencies of $\sim10\%$. Nevertheless, the figures of merit of our structures are comparable with values previously only achieved for QDs emitting at shorter wavelength or by applying technically demanding fabrication processes. Our architecture and the simple fabrication procedure allows for the demonstration of a single-photon generation with purity $\mathcal{P}>98\%$ at the liquid helium temperature and $\mathcal{P}=75\%$ at $80$ K.

cond-mat.mes-hall↗

arXiv2021

Droplet epitaxy symmetric InAs/InP quantum dots for quantum emission in the third telecom window: morphology, optical and electronic properties

The rapidly developing quantum communication technology requires deterministic quantum emitters that can generate single photons and entangled photon pairs in the third telecom window, in order to be compatible with existing optical fiber networks and on-chip silicon photonic processors. InAs/InP quantum dots (QDs) are among the leading candidates for this purpose, due to their high emission efficiency in the required spectral range. However, fabricating versatile InAs/InP QD-based quantum emitters is challenging, especially as these QDs typically have asymmetric profiles in the growth plane, resulting in a substantial bright-exciton fine structure splitting (FSS). This hinders the generation of entangled photon pairs and thus, compromises the versatility of InAs/InP QDs. We overcome this by implementing droplet epitaxy (DE) synthesis of low surface density (2.8$\times$10$^8$ cm$^{-2}$) InAs QDs on an (001)-oriented InP substrate. The resulting QDs are located in etched pits, have concave bases, and most importantly, have symmetric in-plane profiles. We provide an analytical model to explain the kinetics of pit formation and QD base shape modification. Our theoretical calculations of electronic states reveal the properties of neutral and charged excitons and biexcitons confined in such QDs, which agree with the optical investigations of individual QDs. The optical response of QD ensembles suggests that FSS may indeed be negligible, as reflected in the vanishing degree of linear polarization. However, single QD spectrum gathered from an etched mesa shows moderate FSS of (50$\pm$5) $μ$eV that we link to destructive changes made in the QD environment during the post-growth processing. Finally, we show that the studied DE QDs provide a close-to-ideal single-photon emission purity of (92.5$\pm$7.5) $\%$ in the third telecom window.

cond-mat.mes-hall↗

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↗