arXiv subjects

Hamidreza Akbari

Publications and source records attributed to Hamidreza Akbari.

4 recordsLinked to original sources

arXiv2024

Photon statistics analysis of h-BN quantum emitters with pulsed and continuous-wave excitation

We report on the quantum photon statistics of hexagonal boron nitride (h-BN) quantum emitters by analyzing the Mandel Q parameter. We have measured the Mandel Q parameter for h-BN quantum emitters under various temperatures and pump power excitation conditions. Under pulsed excitation we can achieve a Mandel Q of -0.002 and under continuous-wave (CW) excitation this parameter can reach -0.0025. We investigate the effect of cryogenic temperatures on Mandel Q and conclude that the photon statistics vary weakly with temperature. Through calculation of spontaneous emission from an excited two-level emitter model, we demonstrate good agreement between measured and calculated Mandel Q parameter when accounting for the experimental photon collection efficiency. Finally, we illustrate the usefulness of Mandel Q in quantum applications by the example of random number generation and analyze the effect of Mandel Q on the speed of generating random bits via this method.

quant-ph↗

arXiv2023

Rydberg Excitons and Trions in Monolayer MoTe$_2$

Monolayer transition metal dichalcogenide (TMDC) semiconductors exhibit strong excitonic optical resonances which serve as a microscopic, non-invasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS$_2$, MoSe$_2$, WS$_2$ and WSe$_2$), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe$_2$). Here, we report an experimental investigation of excitonic luminescence properties of monolayer MoTe$_2$ to understand the excitonic Rydberg series, up to 3s. We report significant modification of emission energies with temperature (4K to 300K), quantifying the exciton-phonon coupling. Furthermore, we observe a strongly gate-tunable exciton-trion interplay for all the Rydberg states governed mainly by free-carrier screening, Pauli blocking, and band-gap renormalization in agreement with the results of first-principles GW plus Bethe-Salpeter equation approach calculations. Our results help bring monolayer MoTe$_2$ closer to its potential applications in near-infrared optoelectronics and photonic devices.

cond-mat.mes-hall↗

arXiv2022

Lifetime Limited and Tunable Quantum Light Emission in h-BN via Electric Field Modulation

Color centered-based single photon emitters in hexagonal boron nitride (h-BN) have shown promising photophysical properties as sources for quantum light emission. Despite significant advances towards such a goal, achieving lifetime-limited quantum light emission in h-BN has proven to be challenging, primarily due to various broadening mechanisms including spectral diffusion. Here, we propose and experimentally demonstrate suppression of spectral diffusion by applying an electrostatic field. We observe both Stark shift tuning of the resonant emission wavelength, and emission linewidth reduction nearly to the homogeneously broadened lifetime limit. Lastly, we find a cubic dependence of the linewidth with respect to temperature at the homogeneous broadening regime. Our results suggest that field tuning in electrostatically gated heterostructures is promising as an approach to control the emission characteristics of h-BN color centers, removing spectral diffusion and providing the energy tunability necessary for integrate of quantum light emission in nanophotonic architectures.

physics.optics↗

arXiv2021

Nanoscale axial position and orientation measurement of hexagonal boron nitride quantum emitters using a tunable nanophotonic environment

Color centers in hexagonal boron nitride (hBN) have emerged as promising candidates for single-photon emitters (SPEs) due to their bright emission characteristics at room temperature. In contrast to mono- and few-layered hBN, color centers in multi-layered flakes show superior emission characteristics such as higher saturation counts and spectral stability. Here, we report a method for determining both the axial position and three-dimensional dipole orientation of SPEs in thick hBN flakes by tuning the photonic local density of states using vanadium dioxide (VO2), a phase change material. Emitters under study exhibit a strong surface-normal dipole orientation, providing some insight on the atomic structure of hBN SPEs, deeply embedded in thick crystals. We have optimized a hot pickup technique to reproducibly transfer flakes of hBN from VO2 onto SiO2/Si substrate and relocated the same emitters. Our approach serves as a practical method to systematically characterize SPEs in hBN prior to integration in quantum photonics systems.

physics.app-ph↗