arXiv subjects

Kartik Gaur

Publications and source records attributed to Kartik Gaur.

10 recordsLinked to original sources

arXiv2026

An integrated all-van der Waals nanobeam laser

Transition-metal dichalcogenides offer a promising platform for integrated coherent light sources, yet lasing has largely relied on hybrid photonic architectures without direct quantum-optical verification. Here, we demonstrate an all-van der Waals (all-vdW) high-$\beta$ nanobeam laser based on a WS$_2$/MoSe$_2$/WS$_{2}$ heterostructure, with the MoSe$_2$ monolayer directly integrated in the WS$_{2}$-based optical resonator for optimal gain-mode overlap. The devices exhibit efficient exciton-cavity coupling at cryogenic temperatures, strongly directional and linearly polarized emission, soft nonlinear input-output characteristics and linewidth narrowing, enabling lasing operation with $\beta$ near unity. Excitation-power-dependent photon-autocorrelation measurements reveal a transition from thermal to Poissonian photon statistics, with $g_{\mathrm{peak}}^{(2)}(0)$ decreasing from $(1.28\,\pm\,0.09)$ near threshold to $(1.07\,\pm\,0.07)$ above threshold, directly verifying lasing operation. Furthermore, temporal broadening of the autocorrelation uncovers fluctuation-dominated lasing dynamics. These results establish all-vdW heterostructures as a highly attractive platform for integrated coherent light sources in layered-material photonic architectures and scalable quantum-photonic circuits.

physics.optics↗

arXiv2026

Localized Excitonic Emission in Wafer-Scale MOCVD-Grown GaSe 2D Nanosheets for Classical and Non-Classical Light Sources

Wafer-scale growth of two-dimensional semiconductors remains a key challenge for their integration into photonic technologies. While most studies of two-dimensional semiconductors have focused on transition metal dichalcogenides and their scalable fabrication, comparatively little attention has been given to III-VI monochalcogenides. Here, we report wafer-scale growth of gallium selenide (GaSe) by metal-organic chemical vapor deposition (MOCVD) and investigate its structural and optical properties for visible-range classical and quantum light emission. Two samples with thicknesses ranging from a few monolayers to several micrometers, controlled via the growth time, were investigated. The 30-minute grown sample yields intense, broad photoluminescence spanning 1.7--2.0$\,$eV, whereas the thinner 3-minute sample exhibits discrete narrow emission lines and single-photon emission with $(g^{(2)}(0) = 0.15 \pm 0.10)$. Remarkably, cathodoluminescence mapping reveals pronounced spatial localization of both spectrally narrow and broad emission centers. Together with temperature-dependent power-law analysis and Raman mapping, our results indicate defect-induced emission rather than intrinsic excitonic recombination. These findings establish wafer-scale MOCVD grown 2D GaSe as a platform for classical and non-classical light sources and highlight defect-engineered localization as a route toward scalable quantum photonics.

cond-mat.mes-hall↗

arXiv2026

Stark-tunable O-band single-photon sources based on deterministically fabricated quantum dot--circular Bragg gratings on silicon

Semiconductor quantum dots (QDs) offer outstanding quantum-optical properties, making them highly attractive for quantum information technologies. However, combining wide-range electrical tunability, efficient photon extraction, elevated-temperature operation, monolithic silicon integration, and telecom-wavelength compatibility remains a major challenge. Here, we demonstrate electrically contacted circular Bragg grating (eCBG) resonators incorporating InGaAs QDs directly grown on silicon, enabling bright single-photon emission in the telecom O-band. Deterministic electron-beam lithography and a ridge-based vertical p--i--n diode architecture enable precise device integration and electrical control of individual emitters. The QD--eCBGs exhibit a quantum-confined Stark shift of approximately 16 nm (11 meV) at 4 K, representing a record for QDs embedded in nanophotonic structures at telecom wavelengths. This is achieved alongside a photon extraction efficiency of $(21.7 \pm 3.0)\%$ into the first lens, while maintaining excellent radiative properties and high single-photon purity, with $g^{(2)}(0)=0.0078 \pm 0.0012$ below saturation and $g^{(2)}(0)=0.0183 \pm 0.0021$ at saturation under pulsed excitation. Robust antibunching persists up to 77 K, with $g^{(2)}(0)=0.0663 \pm 0.0056$, enabling operation with liquid-nitrogen or compact Stirling cryocoolers. Furthermore, spatially separated QD--eCBGs can be electrically tuned into spectral resonance without degrading photon statistics. These results establish a silicon-compatible, electrically addressable telecom O-band quantum light platform combining wide spectral tunability, high single-photon purity, and elevated-temperature operation, providing a scalable route toward practical photonic quantum networks.

physics.optics↗

arXiv2026

Strain-Engineered Deterministic Quantum Dots for Telecom O-Band Emission Using Buried Stressors

The deterministic realization of quantum light sources operating at telecom wavelengths is essential for long-distance fiber-based quantum communication and distributed quantum computing. In this work, we demonstrate that telecom O-band emission can be achieved from site-controlled InGaAs/GaAs quantum dots (QDs). Our concept utilizes a buried AlAs/Al$_2$O$_3$ stressor layer with the unique feature that induces a well-defined and controllable tensile strain field at the growth surface, enabling both a redshift of QD emission to the $\sim$1.3~\mu m range and site-selective nucleation at the mesa centers. This concept eliminates not only the need for strain-reducing layers (SRLs), which are known to degrade optical coherence, but also provides spatial control and spectral tunability. The grown telecom QDs show pure single-photon emission with $g^{(2)}(\tau) = (5.0 \pm 1.0) \times 10^{-2}$ at 4 K and $(2.8 \pm 0.3) \times 10^{-1}$ at 77~K, demonstrating the quantum nature and thermal stability of the emitters. The emission characteristics of complex excitonic states are analyzed using 8-band $k \cdot p$ and configuration-interaction modeling, which quantitatively reproduces the experimental observations. Finally, we present a theory-supported strategy to further redshift the emission toward the center of the O-band and beyond by employing a multi-buried-stressor approach. This combined framework of experiment and theory establishes the buried stressor concept as a scalable route toward highly coherent, position-controlled O-band quantum emitters compatible with industrial photonic integration.

cond-mat.mes-hall↗

arXiv2025

Scalable Quantum Photonic Platform Based on Site-Controlled Quantum Dots Coupled to Circular Bragg Grating Resonators

The scalable integration of solid-state quantum emitters into photonic nanostructures remains a central challenge for quantum photonic technologies. Here, we demonstrate a robust and streamlined integration strategy that tackles the long-standing issue of deterministic fabrication on randomly positioned self-assembled quantum dots (QDs), leveraging a buried-stressor-based site-controlled InGaAs QD platform. We show that this deterministic growth approach enables precise spatial alignment with circular Bragg grating (CBG) resonators for enhanced emission, eliminating the need for complex and time-consuming deterministic lithography techniques. We fabricated a $6\times6$ SCQD-CBG array with 100\% device yield, with 35 devices falling within the radial-offset range where the simulated photon-extraction efficiency (PEE) exceeds 20\%, underscoring the spatial precision and scalability of our fabrication concept. A systematically selected subset of five devices with varying radial displacements reveals clear offset-dependent trends in extraction efficiency, spectral linewidth, and photon indistinguishability, thereby establishing quantitative bounds on spatial alignment tolerances. In the best-aligned QD-CBG device, we achieve a PEE of $(47.1\pm3.8)\%$, a linewidth of $(1.41\pm0.22)$ GHz, a radiative decay lifetime of $(0.80\pm0.02)$~ns, a single-photon purity of $(99.58\pm0.18)\%$, and a Hong-Ou-Mandel two-photon interference visibility of $(81\pm5)\%$ under quasi-resonant excitation at saturation power. We confirm our conceptual understanding of the effect of emitter-position dependent charge-noise fluctuations in terms of a quantum-optical model for the (quantum-)emission properties.

cond-mat.mes-hall↗

arXiv2025

Direct Epitaxial Growth and Deterministic Device Integration of high-quality Telecom O-Band InGaAs Quantum Dots on Silicon Substrate

Semiconductor quantum dots (QDs) are key building blocks for photonic quantum technologies, enabling practical sources of non-classical light. A central challenge for scalable integration is the direct epitaxial growth of high-quality emitters on industry-compatible silicon platforms. Furthermore, for long-distance fiber-based quantum communication, emission in the telecom O- or C-band is essential. Here, we demonstrate the direct growth of high-quality InGaAs/GaAs QDs emitting in the telecom O-band using a strain-reducing layer approach on silicon. Deterministic integration of individual QDs into circular Bragg grating resonators is achieved via in-situ electron-beam lithography. The resulting devices exhibit strong out-coupling enhancement, with photon extraction efficiencies up to $(40 \pm 2)\%$, in excellent agreement with numerical simulations. These results highlight the high material quality of both the epitaxial platform and the photonic nanostructure, as well as the precise lateral positioning of the emitter within 20~nm of the resonator center. At cryogenic temperature (4~K) and low excitation power ($0.027\times P_\text{sat}$), the devices show excellent single-photon purity, exceeding 99\%. Operation at elevated temperatures of 40~K and 77~K, compatible with compact Stirling cryo-coolers and liquid-nitrogen cooling, reveals robust performance, with single-photon purity maintained at $(88.4 \pm 0.6)\%$ at 77~K. These results demonstrate a practical and scalable route toward silicon-based quantum light sources and provide a promising path for cost-effective fabrication and seamless integration of quantum photonics with classical electronics, representing an important step toward large-scale, chip-based quantum information systems.

cond-mat.mes-hall↗

arXiv2025

Deterministic nanofabrication of quantum dot-circular Bragg grating resonators with high process yield using in-situ electron beam lithography

The controlled integration of quantum dots (QDs) as single-photon emitters into quantum light sources is essential for the implementation of large-scale quantum networks. In this study, we employ the deterministic in-situ electron-beam lithography (iEBL) nanotechnology platform to integrate individual QDs with high accuracy and process yield into circular Bragg grating (CBG) resonators. Notably, CBG devices comprising just 3 to 4 rings exhibit photon extraction efficiencies comparable to those of structures with more rings. This facilitates faster fabrication, reduces the device footprint, and enables compatibility with electrical contacting. To demonstrate the scalability of this process, we present results of 95 optically active QD-CBG devices fabricated across two lithography sessions. These devices exhibit bright, narrow-linewidth single-photon emission with excellent optical quality. To evaluate QD placement accuracy, we apply a powerful characterization technique that combines cathodoluminescence (CL) mapping and scanning electron microscopy. Statistical analysis of these devices reveals that our iEBL approach enables high alignment accuracy and a process yield of over >90% across various CBG geometries. Our findings highlight a reliable route toward the scalable fabrication of high-performance QD-based single-photon sources for use in photonic quantum technology applications.

cond-mat.mes-hall↗

arXiv2025

Enhancement of Indistinguishable Photon Emission from a GaAs Quantum Dot via Charge Noise Suppression

The generation of indistinguishable single photons is a fundamental requirement for future quantum technologies, particularly in quantum repeater networks and for distributed quantum computing based on entanglement distribution. However, spectral jitter, often induced by charge noise in epitaxial quantum dots, leads to exciton dephasing, thereby limiting their practical usage in quantum applications. We present a straightforward approach to mitigate charge noise-induced decoherence in droplet-etched GaAs quantum dots embedded in an n-i-p diode structure and integrated deterministically into an electrically contacted circular Bragg grating resonator for emission enhancement. The quantum device allows for the stabilization of the charge environment by applying an external electrical field while producing a photon extraction efficiency of approximately (37 +- 2)%. Hong-Ou-Mandel two-photon interference measurements reveal a strong voltage dependence of the exciton dephasing time and interference visibility on the applied bias in excellent agreement with our theoretical predictions. Notably, the reduction in visibility from a maximum, charge-stabilized corrected value of 97 percent at the optimum bias point follows an inverse square dependence (proportional to 1/I^2) with increasing diode current (I) in forward direction. Under a quasi-resonant excitation scheme, we achieve a maximum exciton dephasing time (T2*) of approximately (6.8 +-0.5) ns, reaching nearly the Fourier limit (T2 = 2T1) without the need for complex echo schemes like Ramsey or Carr-Purcell-Meiboom-Gill sequences. These findings are consistent with theoretical predictions from rate equation modeling and quantum optical analysis as well as voltage-dependent linewidth measurements, demonstrating optimized electrical control of exciton dephasing.

cond-mat.mes-hall↗

arXiv2025

On-demand storage and retrieval of single photons from a semiconductor quantum dot in a room-temperature atomic vapor memory

Interfacing light from solid-state single-photon sources with scalable and robust room-temperature quantum memories has been a long-standing challenge in photonic quantum information technologies due to inherent noise processes and time-scale mismatches between the operating conditions of solid-state and atomic systems. Here, we demonstrate on-demand storage and retrieval of single photons from a semiconductor quantum dot device in a room-temperature atomic vapor memory. A deterministically fabricated InGaAs quantum dot light source emits single photons at the wavelength of the cesium D1 line at 895\,nm which exhibit an inhomogeneously broadened linewidth of 5.1(7)\,GHz and are subsequently stored in a low-noise ladder-type cesium vapor memory. We show control over the interaction between the single photons and the atomic vapor, allowing for variable retrieval times of up to 19.8(3)\,ns at an internal efficiency of $η_\mathrm{int}=0.6(1)\%$. Our results significantly expand the application space of both room-temperature vapor memories and semiconductor quantum dots in future quantum network architectures.

quant-ph↗

arXiv2023

High-$β$ lasing in photonic-defect semiconductor-dielectric hybrid microresonators with embedded InGaAs quantum dots

We report an easy-to-fabricate microcavity design to produce optically pumped high-$β$ quantum dot microlasers. Our cavity concept is based on a buried photonic-defect for tight lateral mode confinement in a quasi-planar microcavity system, which includes an upper dielectric distributed Bragg reflector (DBR) as a promising alternative to conventional III-V semiconductor DBRs. Through the integration of a photonic-defect, we achieve low mode volumes as low as 0.28 $μ$m$^3$, leading to enhanced light-matter interaction, without the additional need for complex lateral nanoprocessing of micropillars. We fabricate semiconductor-dielectric hybrid microcavities, consisting of Al$_{0.9}$Ga$_{0.1}$As/GaAs bottom DBR with 33.5 mirror pairs, dielectric SiO$_{2}$/SiN$_x$ top DBR with 5, 10, 15, and 19 mirror pairs, and photonic-defects with varying lateral size in the range of 1.5 $μ$m to 2.5 $μ$m incorporated into a one-$λ/n$ GaAs cavity with InGaAs quantum dots as active medium. The cavities show distinct emission features with a characteristic photonic defect size-dependent mode separation and \emph{Q}-factors up to 17000 for 19 upper mirror pairs in excellent agreement with numeric simulations. Comprehensive investigations further reveal lasing operation with a systematic increase (decrease) of the $β$-factor (threshold pump power) with the number of mirror pairs in the upper dielectric DBR. Notably, due to the quasi-planar device geometry, the microlasers show high temperature stability, evidenced by the absence of temperature-induced red-shift of emission energy and linewidth broadening typically observed for nano- and microlasers at high excitation powers.

physics.optics↗