arXiv subjects

Ikshvaku Shyam

Publications and source records attributed to Ikshvaku Shyam.

4 recordsLinked to original sources

arXiv2026

Deterministic single-photon sources in hexagonal boron nitride with electron-dose-tuned purity and reversible thermal quenching

Electron-beam irradiation is an established route to create site-controlled, room-temperature single-photon emitters (SPEs) in hexagonal boron nitride (hBN), but two aspects remain underexplored: how the electron dose governs the properties of the resulting single emitters, and how the emission behaves when the host is heated above room temperature. Here, we create emitters deterministically with a focused electron beam and confirm single-photon emission across three independent flakes, with $g^{(2)}(0)=0.09$, $0.12$, and $0.16$. We map the single-emitter response (yield, spectrum, lifetime, and photon purity) as a function of electron dose, identifying an optimal window for high-purity single emitters. Consistent with recent cryogenic studies, we assign the bright room-temperature feature near 575 n to the phonon sideband (PSB) of a green--yellow emitter whose zero-phonon line (ZPL) lies near 548 nm. Temperature-dependent photoluminescence measured in situ under real-time from room temperature to 300 degrees C reveals a thermal quenching that is fully reversible upon cooling, in contrast to the irreversible annealing-induced degradation reported elsewhere, indicating that transient heating does not permanently damage the centers. These results add quantitative dose control and above-room-temperature operation to the toolbox for deterministic hBN quantum-light sources.

physics.optics↗

arXiv2026

Hexagonal Boron Nitride Spin Defects for Quantum Photonics: Annealing-Free Generation by Krypton Ion Implantation

Controlled, reproducible generation of luminescent defect centres in hBN remains a key challenge for scalable quantum-photonic technologies. Here, we report Kr$^{+}$ ion implantation as a tunable, annealing-free, and chemically inert route to room-temperature near-infrared luminescent spin defects in hBN, requiring no pre- or post-implantation annealing. SRIM Monte Carlo simulations were used to optimise the parameters for 40 keV Kr$^{+}$ irradiation of hBN flakes. The implanted samples exhibit a stable near-infrared photoluminescence (PL) band centred at $\sim$830 nm whose intensity increases with implantation fluence over $10^{11}$-$10^{15}$ions/cm$^{2}$. Temperature-dependent PL measurements (20-300 K) reveal a linewidth broadening well described by a $T^{3}$ dependence, consistent with acoustic-phonon-mediated dephasing. Raman spectra show the characteristic $E_{2g}$ mode of pristine hBN at $\sim$1366 cm$^{-1}$ alongside an implantation-induced defect feature at $\sim$1295 cm$^{-1}$, confirming irradiation-induced lattice disorder. Electron paramagnetic resonance (EPR) measurements reveal a paramagnetic centre with a $g$-factor of 2.003, and density functional theory (DFT) calculations indicate that a spatially separated $V_{\mathrm{N}}$-$C_{\mathrm{B}}$ donor-acceptor pair complex is a viable origin of the observed optical and magnetic signatures. Overall, Kr$^{+}$ implantation offers an effective, annealing-free, and scalable platform for generating stable room-temperature luminescent defects, providing a promising route toward quantum photonics.

physics.optics↗

arXiv2026

Deterministic Single-Photon Emitter Arrays in Hexagonal Boron Nitride by Carbon-Assisted Focused Ion Beam Engineering

The realization of on-chip photonic circuits requires scalable and deterministic single-photon emitters (SPEs) at room temperature, which remain a challenge in van der Waals materials. In this work, we report a novel three-step fabrication process for the generation of spatially controlled SPE arrays in hexagonal boron nitride (hBN). The process comprises site-selective gallium (Ga) focused ion beam milling, nanoscale conformal carbon deposition over the patterned regions, and subsequent thermal annealing. The synergistic combination of these steps resulted in a site-correlated emitter yield of ($\sim 89\%$) across 100 fabrication sites. Second-order autocorrelation measurements revealed pronounced three-level emitter dynamics where the best emitters exhibited high purity ($g^{(2)}(0)=0.15 \pm 0.09$).To the best of our knowledge, this is the first lithography-free, direct-write approach combining Ga-ion milling, selective carbon engineering, and thermal annealing to deterministically generate \hBN{} \SPE{}s. The reproducibility of the method is validated across multiple independently fabricated samples. These results establish a scalable, lithography-free pathway toward on-demand SPE arrays relevant to integrated quantum photonics.

physics.optics↗

arXiv2024

Interplay of plasmonics and strain for Hexagonal Boron Nitride emission engineering

In the realm of quantum information and sensing, there has been substantial interest in the single-photon emission associated with defects in hexagonal boron nitride (hBN). With the goal of producing deterministic emission centers, in this work, we present a platform for engineering emission in hBN integrated with gold truncated nanocone structures. Our findings highlights that, the activation of emission is due to the truncated gold nanocones. Furthermore, we measure the quantum characteristics of this emission and find that while our system demonstrates support for single-photon emission, the origin of this emission remains ambiguous. Specifically, it is unclear whether the emission arises from defects generated by the induced strain or from alternative defect mechanisms. This uncertainty stems from the fluorescence properties inherent to gold, complicating our definitive attribution of the quantum emission source. To provide a rigorous theoretical foundation, we elucidate the effects of strain via the Kirchhoff-Love theory. Additionally, the enhancements observed due to plasmonic effects are comprehensively explained through the resolution of Maxwell's equations. This study will be useful for the development of deterministic and tunable single photonic sources in two dimensional materials and their integration with plasmonic platforms.

physics.optics↗