arXiv subjects

Mouli Hazra

Publications and source records attributed to Mouli Hazra.

6 recordsLinked to original sources

arXiv2026

Insights into the Nature of Quantum Emitters in Electron-Irradiated hexagonal Boron Nitride

Quantum emitters in hexagonal boron nitride (hBN) have emerged as a promising solid-state platform for quantum technology applications. However, a persistent challenge in the field is the unclear origin of many observed emission lines, particularly in the visible range, which can be difficult to distinguish from signals arising from organic or process-induced contamination during sample preparations and handling. This ambiguity limits both the reproducibility of emitter generation and the reliable identification of truly intrinsic quantum defects. This work provides a step-by-step framework to assess whether quantum emitters in electron-irradiated hBN are associated with organic contaminants introduced during sample preparation. We employ hyperspectral imaging, thermal annealing, and oxygen plasma etching to investigate the origin of the green-yellow emitters in electron-irradiated hBN. The combined results not only rule out organic contamination as the source of emission but also provide insight into the spectral variability, thermal stability, and vertical localization of the emitters generated in electron-irradiated hBN that was created without any pre- or post-processing. In addition, our experiments demonstrate the feasibility of creating stable emitters in hBN with thicknesses below 10 nm. These findings provide practical guidance for the identification and controlled implementation of hBN-based single-photon emitters in quantum photonic devices.

physics.optics↗

arXiv2026

Temperature-Dependent Emission Spectroscopy of Quantum Emitters in Hexagonal Boron Nitride

Color centers in hexagonal boron nitride (hBN) have attracted significant interest due to their potential applications in future optical quantum technologies. For most applications, scalable on-demand fabrication is a key requirement. Recent advances using localized electron irradiation have demonstrated near-identical emitters in the blue and yellow spectral regions. While the blue emitters have been demonstrated in cryogenic temperatures, the yellow emitters remain uncharacterized under such conditions. In this work, we therefore extended the study of yellow emitters to cryogenic temperatures. Initially, multiple spectral features were observed, prompting a systematic investigation that led to the identification of a defect emission centered around 547.5 nm with high brightness and excellent photostability. By tuning the excitation wavelength, we are able to distinguish Raman scattering peaks from the emitter emission. Further analysis of the vibronic emissions allowed us to identify an optical phonon mode, whose contribution becomes increasingly dominant at elevated temperatures. Photoluminescence excitation spectroscopy (PLE) reveals excitation through this phonon mode enhances the emission by almost 5-fold in cryogenic temperature. Temperature-dependent studies further elucidate the role of phonons in the emission process. These observations deepen our understanding of the nature of the emitters, opening new avenues for precise tuning of quantum light sources.

physics.optics↗

arXiv2026

Transition Dipole Rotation Beyond the Condon Approximation in Single hBN Quantum Emitters

The design of polarization-encoded quantum interfaces relies on the assumption that solid-state emitters possess static transition dipoles defined by the host lattice symmetry. Here, we demonstrate that the transition dipole moment of single hexagonal boron nitride quantum emitters is not a static property but rotates as a function of photon energy. Through high-resolution energy-resolved spectroscopy, we reveal a continuous rotation of the emission dipole orientation reaching up to $40^{\circ}$ across the vibronic manifold at room temperature, driven by coupling to the phonon bath. This spectral rotation is effectively suppressed at cryogenic temperatures (6 K), where the acoustic phonon population is negligible, identifying thermally activated lattice vibrations as the primary driver of the reorientation. First-principles calculations on two representative defects spanning weak and strong electron-phonon coupling regimes confirm that phonon-displaced geometries produce a systematic deviation of the transition dipole orientation from the zero-phonon line, with the magnitude scaling with vibronic coupling strength. The experimental observations and calculations demonstrate that single quantum emitters can operate beyond the Condon approximation, with the transition dipole acquiring a dependence on the instantaneous nuclear configuration. Our results identify a fundamental limit for polarization fidelity in solid-state quantum networks and connect solid-state single-emitter physics to a class of effects previously accessible only in ensemble measurements in molecular and biological spectroscopy.

quant-ph↗

arXiv2025

All-dry pick-up and transfer method for quantum emitter arrays in hexagonal boron nitride

Single photon emitters in hexagonal boron nitride are based on fluorescent point-like defects. These defects typically have exceptional photophysical properties and therefore been the focus of extensive research due to their potential to advance photonic quantum technologies. However, achieving scalable integration of these emitters to arbitrary platforms with high yield while retaining their characteristics remains a significant challenge, particularly when the target substrate is not compatible with the fabrication method. In this work, we introduce an all-dry transfer method aimed at addressing these challenges with improved effectiveness compared to existing techniques. This polymer stamp-assisted transfer method maintains high output and preserves the fundamental characteristics of the emitters while eliminating wet chemical processes. A comprehensive post-transfer characterization verified not only the maintenance of the defining characteristic of a single photon emitter, the second-order correlation function $g^{(2)}(0)$, but also showed improvement by about 46%. In contrast, the lifetime, emission spectrum, and the photostability showed only negligible change, demonstrating that the characteristics of the emitters were retained during the transfer process. This transfer technique has success rate of 81.8%, determined by the proportion of single photon emitters that retain their optical and preserve physical structure post-transfer. This high success rate shows the potential to scale the integration of single photon emitters across diverse platforms. We expect that this process contributes to the applications of boron nitride defects in quantum technologies.

physics.optics↗

arXiv2024

Comparative study of quantum emitter fabrication in wide bandgap materials using localized electron irradiation

Quantum light sources are crucial foundational components for various quantum technology applications. With the rapid development of quantum technology, there has been a growing demand for materials with the capability of hosting quantum emitters. One such material platform uses fluorescent defects in hexagonal boron nitride (hBN) that can host deep sublevels within the bandgap. The localized electron irradiation has shown its effectiveness in generating deep sublevels to induce single emitters in hBN. The question is whether localized (electron beam) irradiation is a reliable tool for creating emitters in other wide bandgap materials and its uniqueness to hBN. Here, we investigate and compare the fabrication of quantum emitters in hBN and exfoliated muscovite mica flakes along with other 3D crystals, such as silicon carbide and gallium nitride, which are known to host quantum emitters. We used our primary fabrication technique of localized electron irradiation using a standard scanning electron microscope. To complement our experimental work, we employed density functional theory simulations to study the atomic structures of defects in mica. While our fabrication technique allows one to create hBN quantum emitters with a high yield and high single photon purity, it is unable to fabricate single emitters in the other solid-state crystals under investigation. This allows us to draw conclusions on the emitter fabrication mechanism in hBN, which could rely on activating pre-existing defects by charge state manipulation. Therefore, we provide an essential step toward the identification of hBN emitters and their formation process.

physics.app-ph↗

arXiv2022

Nonlinear polarization holography of nanoscale iridium films

The phasing problem of heterodyne-detected nonlinear spectroscopy states that the relative time delay between the exciting pulses and a local oscillator must be known with subcycle precision to separate absorptive and dispersive contributions. Here, a solution to this problem is presented which is the time-domain analogue of holographic interferometry, in which the comparison of two holograms reveals changes of an objects size and position with interferometric precision (i.e. to fractions of a wavelength of light). The introduced method, called nonlinear polarization holography, provides equivalent information as attosecond nonlinear polarization spectroscopy but has the advantage of being all-optical instead of using an attosecond streak camera. Nonlinear polarization holography is used here to retrieve the time-domain nonlinear response of a nanoscale iridium film to an ultrashort femtosecond pulse. Using density matrix calculations it is shown that the knowledge of the nonlinear response with subcycle precision allows to distinguish excitation and relaxation mechanisms of low-energetic electrons that depend on the nanoscale structure of the iridium film.

physics.optics↗