Mohamed Benyoucef

Investigating single-photon dynamics is crucial for characterization of single-photon emitters. Here, we demonstrate a telecom-band quantum dot single-photon emitter integrated with a lithographically aligned double solid immersion lens structure, achieving a collection efficiency of 18(3)% at the first lens. Using two-time correlation measurements, we observed re-excitation-induced multiphoton emission arising from a long-lived, carrier-induced capture process under non-resonant excitation. Under quasi-resonant excitation, this effect was strongly suppressed, reducing the multiphoton emission probability within a 3 ns window from 0.052(1) to 0.0163(4). We further performed second-order quantum spectroscopy based on Fourier analysis of the Hong–Ou–Mandel interference, enabling direct extraction of the exciton fine-structure splitting. This work provides a direct characterization of re-excitation dynamics and coherence properties in a telecom-band single-photon emitter.

We demonstrate the integration of molecular beam epitaxy (MBE)-grown InAs/InP quantum dots (QDs) on gold thin films, achieving a fivefold enhancement of telecom-wavelength emission compared with QDs grown on distributed Bragg reflectors (DBRs). Micro-photoluminescence (µ-PL) spectroscopy reveals a pronounced increase in PL intensity from the Au-integrated structures, highlighting the enhanced optical response enabled by the metallic mirror effect. Reflectivity measurements exhibit a characteristic dip near the QD emission wavelength, indicating increased optical absorption and reduced reflectance, consistent with improved coupling of incident light into the fabricated structure. Power-dependent measurements demonstrate background-free exciton and biexciton emission from single QDs with resolution-limited linewidths. Polarization-dependent measurements further reveal an ultra-small excitonic fine-structure splitting, reaching values as low as ~2 μeV. Finally, statistical analysis of multiple QDs confirms the reproducibility and robustness of the observed optical properties.

Van der Waals indium selenide is a promising material for next-generation optoelectronics due to its thickness-dependent band structure and high carrier mobility. Here, we investigate the optical properties of size-selected liquid-phase exfoliated γ-InSe nanosheets. The dispersions, composed of flakes with lateral dimensions below 100 nm, exhibit pronounced structural disorder and size-dependent optical behavior. Absorbance spectroscopy reveals systematic changes across size-selected fractions, enabling the extraction of quantitative metrics for estimating nanosheet lateral size and layers number. In addition, stability studies demonstrate significant degradation under ambient conditions, which is accelerated at elevated temperatures. Photoluminescence measurements on nanosheets exfoliated under inert conditions show broad, asymmetric emission with a clear blue-shift for smaller flakes, reflecting quantum confinement and dielectric screening effects. The emission characteristics further indicate a dominant contribution from localized states associated with disorder. These findings provide insight into the structure–property relationships in liquid-phase exfoliated γ-InSe and highlight its potential for solution-processed optoelectronic applications.

We demonstrate the integration of molecular beam epitaxy (MBE)-grown InP-based quantum dots (QDs) on gold thin films, achieving a fivefold enhancement of emission at telecom wavelengths compared with QDs grown on distributed Bragg reflectors (DBRs). Micro-photoluminescence (µ-PL) spectroscopy reveals a pronounced enhancement of the PL intensity, which is attributed to plasmon-assisted light–matter interaction at the metal–semiconductor interface. Reflectivity measurements reveal a characteristic dip near the QD emission wavelength, consistent with the excitation of surface plasmon resonances (SPRs), indicating favorable spectral overlap between the plasmonic modes and the QD emission. Power-dependent measurements reveal background-free exciton and biexciton emission from single QDs with resolution-limited linewidths. Polarization-dependent measurements demonstrate an ultra-small excitonic fine-structure splitting as low as ~2 μeV. Finally, a statistical analysis of multiple QDs confirms the reproducibility of the observed optical properties.

We investigate the spin properties of charge carriers in vertically coupled InAs/InAlGaAs quantum dots grown by molecular beam epitaxy, emitting at telecom C-band wavelengths, with a silicon δ -doped layer. Using time-resolved pump-probe Faraday ellipticity measurements, we systematically study single-, two-, and four-layer quantum dot (QD) configurations to quantify how vertical coupling affects key spin-coherence parameters. Our measurements reveal distinct layer-dependent effects: (i) Adding a second QD layer flips the resident charge from electrons to holes, consistent with optically induced electron tunneling into lower-energy dots and resultant hole charging. (ii) Starting from the four-layer sample, the pump-probe signal develops an additional nonoscillating, decaying component absent in single- and two-layer samples, attributed to multiple layer growth changing the strain environment, which reduces heavy-hole and light-hole mixing. (iii) With four layers or more, hole spin mode locking (SML) can be observed, enabling quantitative extraction of the hole coherence time T 2 ≈ 13 ns from SML amplitude saturation. We also extract longitudinal spin relaxation ( T 1 ) and transverse ( T 2 * ) spin dephasing times, g-factors, and inhomogeneous dephasing parameters for both electrons and holes across all layer configurations. The hole spin dephasing times T 2 * remain relatively constant (2.3–2.7 ns) across layer counts, while longitudinal relaxation times T 1 decrease with increasing layers (from 0.9 µ s for single-layer to 0.32 µ s for four-layer samples). These findings provide potential design guidelines for engineering spin coherence in telecom-band QDs for quantum information applications.

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 Hanle effect demonstration in single InAs(P)/InP QDs emitting predominantly in the S-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 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 T2*=1.53 ± 0.68 ns. Despite the large indium nuclear spin, the obtained T2* 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.

Scalable, reliable quantum light sources are essential for increasing quantum channel capacity and advancing quantum protocols based on photonic qubits. Although recent developments in solid‐state quantum emitters have enabled the generation of single photons with high performance, the scalable integration of multiple quantum light sources onto practical optical platforms remains a challenging task. Here, a breakthrough in achieving a multiple, tunable array of quantum photonic devices is presented. An individual device transfer process allows post‐characterization and selective integration of multiple single‐photon sources onto a V‐groove fiber platform. The nanophotonic cavity ensures efficient coupling of single photons into a standard SMF 28 fiber. Moreover, applying an electric field enables a frequency shift of the integrated single‐photon device. Therefore, the fiber‐integrated quantum platform realizes a scalable and reliable single‐photon array within a compact fiber chip at telecom wavelengths.

We demonstrate that optical excitation of InAs quantum dots (QDs) embedded directly in an InP matrix can be mediated via states in a quaternary compound constituting an InP/InGaAlAs bottom distributed Bragg reflector (DBR) and native defects in the InP matrix. It does not only change the carrier relaxation in the structure but could also lead to the imbalanced occupation of QDs with charge carriers, because the band structure favors the transfer of holes. Thermal activation of carrier transfer can be observed as an increase in the emission intensity versus temperature for excitation powers below saturation on the level of both an inhomogeneously broadened QD ensemble and single QD transitions. That increase in the QD emission is accompanied by a decrease in the emission from the InGaAlAs layer at low temperatures. Finally, carrier transfer between the InGaAlAs layer of the DBR and the InAs/InP QDs is directly proven by the photoluminescence excitation spectrum of the QD ensemble. The reported carrier transfer can increase the relaxation time of carriers into the QDs and thus be detrimental to the coherence properties of single and entangled photons. It is important to take it into account while designing QD-based devices.