arXiv subjects

Rituraj

Publications and source records attributed to Rituraj.

8 recordsLinked to original sources

arXiv2025

Efficient Two Photon Generation from an Emitter in a Cavity

Two-photon states are essential for fundamental applications in quantum information. One of the primary methods of two-photon generation is based on parametric down-conversion, but this suffers from low efficiency and a large footprint. This work presents a detailed theoretical investigation of an alternative approach: two-photon generation from an emitter in a doubly resonant cavity. The system is modelled by the Lindblad master Equation, and an approximate analytical solution is derived to determine the experimentally achievable limits on efficiency and brightness. Additionally, the optimal cavity parameters for achieving these limits are also identified. For experimentally feasible parameters, the maximum efficiency is approximately 35%, which is significantly higher than that of parametric down-conversion-based methods. The optimal rate and efficiency for two-photon generation are achieved when the outcoupling rate of the cavity mode at the two-photon emission frequency matches the single-photon atom-field coupling strength. Moreover, the outcoupling rate of the cavity mode at the one-photon emission frequency for single photons should be minimized. The cavity field properties are also examined by studying the second-order correlation function at zero time delay and the Mandel Q parameter, revealing highly bunched two-photon emission and super-Poissonian statistics. The quantum-jump framework, combined with Monte Carlo simulations, is used to characterize the mechanism of two-photon emission and the emission spectra of the cavity. Two-photon emission is demonstrated to be a rapid cascade process of quantum jumps, and its spectrum consists of three prominent peaks corresponding to transitions between the dressed states of the system.

quant-ph↗

arXiv2024

Wavelength-Agnostic Metasurface Design for Next-Generation 2D Photodetectors

We explore a versatile technique for inverse designing 2D photonic crystal metasurfaces. These surfaces, known for their ability to manipulate light-matter interactions, can be precisely controlled to achieve specific functionalities. The key lies in efficiently optimizing the geometric patterns and dimensions of the metasurface. Through a composite method which exploits two well-established paradigms - Covariance Matrix Adaptation optimization and Rigorous Coupled Wave Analysis (RCWA), we demonstrate our ability to design and optimize resonances in metaelements to achieve desired optical performance such as near-perfect absorption at chosen wavelengths/optical modes, which otherwise proves to be challenging or even impossible with conventional inverse design implementations. We apply our method to design three-layered structures involving a monolayer absorber, transparent metasubstrate, and a back mirror to get near 100% absorption at one or two chosen wavelengths. For illustration, we choose black phosphorus and silicon metasurface to predict ~100% absorption in a monolayer at 1550 nm. The versatile technique can be applied to tailor reflectance and transmittance for any optical mode and wavelength. This computationally efficient design method paves the way for creating high-performance 2D metasurface-based devices with a variety of applications, including quantum technology components such as single photon sensors and biphoton sources, communication systems, and non-linear light conversion.

physics.optics↗

arXiv2024

New design paradigm for highly efficient and low noise photodetector

Achieving high quantum efficiency (QE) with low dark count is essential for highly sensitive photodetectors (PDs), including single photon avalanche detectors (SPADs). However, high QE requires a thicker absorber region, which leads to high dark current and noise, which in turn affects the detectivity of PDs and the photodetection efficiency and dark count of SPADs.The holy grail of photodetector and avalanche photodiode designs is to achieve highest QE with thinnest absorber and still enable large avalanche to gain as needed. We have developed a new design paradigm which exploits the coupling between dielectric Mie resonance and transverse propagating waves in thin layers. The Mie resonance launches the incident light at an angle in an ultrathin absorber, and when coupled to transverse waves, the light propagates laterally and is fully absorbed owing to the longer optical path. Consequently, with appropriate choice of materials for a chosen wavelength, a high absorption(~90%) within typically <100 nm absorber thickness is possible. For illustration, we apply our approach to design Si-based detector operating at 810 nm and InGaAs-based detector operating at 1550 nm and predict that the dark current at room temperature is reduced at least by two orders of magnitude. In addition, the lateral distances are often in a few microns and hence these designs can potentially enable avalanching for a large optical gain.

physics.app-ph↗

arXiv2024

Resonant structure for improved directionality and extraction of single photons

Fluorescent atomic defects, especially in dielectric materials, such as diamond are quite promising for several emerging quantum applications. However, efficient light extraction, directional emission, and narrow spectral emission are key challenges. We have designed dielectric metasurface exploiting Mie-resonance and the Kerker condition to address these issues. Our designed diamond metasurface, tailored for nitrogen-vacancy (NV) defect centers in diamond, predicts up to 500x improvement in the collection of 637 nm (zero phonon line) photons over that from the bare diamond. Our design achieves highly directional emission, predominantly emitting in a 20 degree lobe in the forward direction. This makes light collection more efficient, including for fiber-based collection. The predicted results are stable against the position of the emitter placed in the metaelement, thus alleviating the challenging fabrication requirement of precise positioning of the defect center. Equally importantly, our design approach can be applied to enhance single photon emission also from other defects such as SiV, other materials such as hBN, and other sources such as quantum dots.

physics.optics↗

arXiv2024

Highly sensitive and efficient 1550 nm photodetector for room temperature operation

Photonic quantum technologies such as effective quantum communication require room temperature (RT) operating single- or few- photon sensors with high external quantum efficiency (EQE) at 1550 nm wavelength. The leading class of devices in this segment is avalanche photodetectors operating particularly in the Geiger mode. Often the requirements for RT operation and for a high EQE are in conflict, resulting in a compromised solution. We have developed a device which employs a two-dimensional (2D) semiconductor material on a co-optimized dielectric photonic crystal substrate to simultaneously decrease the dark current by three orders of magnitude at RT and maintain an EQE of >99%. The device is amenable to avalanching and form a basis for single photon detection with ultra-low dark current and high photodetection efficiency. Harnessing the high carrier mobility of 2D materials, the device has ~ps jitter time and can be integrated into a large 2D array camera.

physics.optics↗

arXiv2022

Detecting the relative phase between different frequency components of a photon using a three-level $\Lambda$ atom coupled to a waveguide

We study the scattering of a single photon propagating along a waveguide in an arbitrary superposition state two frequencies with a single three-level $\Lambda$ atom in a superposition of two non-degenerate ground states where the atom is coupled to a waveguide. We find that the scattering depends on both the relative phase between the photon frequencies and the relative phase between the atomic ground states. Our results show that a three-level $\Lambda$ atom coupled to a waveguide can be used as photon phase filter that could detect the relative phase between the two frequencies of the photon superposition state.

quant-ph↗

arXiv2022

Parametric Mie resonances and directional amplification in time-modulated scatterers

We provide a theoretical description of light scattering by a spherical particle whose permittivity is modulated in time at twice the frequency of the incident light. Such a particle acts as a finite-sized photonic time crystal and, despite its sub-wavelength spatial extent, can host optical parametric amplification. Conditions of parametric Mie resonances in the sphere are derived. We show that time-modulated materials provide a route to tailor directional light amplification, qualitatively different from that in scatterers made from a gain media. We design two characteristic time-modulated spheres that simultaneously exhibit light amplification and desired radiation patterns, including those with zero backward and/or vanishing forward scattering. The latter sphere provides an opportunity for creating shadow-free detectors of incident light.

physics.optics↗

arXiv2021

Photonic Chern insulators from two-dimensional atomic lattices interacting with a single surface plasmon polariton

We study the polaritonic bandstructure of two-dimensional atomic lattices coupled to a single excitation of a surface plasmon polariton mode. We show the possibility of realizing topological gaps with different Chern numbers by having resonant atomic transitions to excited states with different angular momentum. We employ a computational method based on the recently proposed Dirichlet-to-Neumann (DtN) map technique which accurately models non-Markovian dynamics as well as interactions involving higher-order electric and magnetic multipole transitions. We design topologically robust edge states which are used to achieve unidirectional emission and non-reciprocal transmission of single photons. We also point out the challenges in realizing bands with higher Chern numbers in such systems.

physics.optics↗