arXiv subjects

Ankit Kundu

Publications and source records attributed to Ankit Kundu.

7 recordsLinked to original sources

arXiv2026

Few-Body Decay Dynamics in Colloidal CsPbI3 Quantum-Dot Clusters

Colloidal perovskite quantum dots combine bright emission with the ability to self- assemble into closely spaced structures, enabling radiative dynamics to be studied from isolated emitters to few-dot clusters. Here, we characterize CsPbI3 perovskite quan- tum dots from isolated emitters to self-assembled clusters containing up to ten dots. We estimate the number of emitters in each cluster using a combination of photon autocorrelation, blinking statistics, and emission brightness. Compared with isolated dots, clusters containing two or more emitters exhibit biexponential decay, with a short lifetime that decreases with emitter number and an additional long-lived component. Photon-correlation Fourier spectroscopy shows that the single-dot emission remains far from the lifetime-limited regime. Nevertheless, we observe emitter-number-dependent decay dynamics even in this low-coherence regime. Together, these measurements es- tablish self-assembled perovskite quantum-dot clusters as a platform for studying how collective optical behavior emerges between the single-emitter and ensemble limits

quant-ph↗

arXiv2026

First order Maxwell operator formalism for macroscopic quantum electrodynamics

Standard macroscopic QED is built on the second-order Green's function for the electric field and discards open-system boundary terms. Here we develop a first-order electromagnetic operator approach that retains both $\mathbf{E}$ and $\mathbf{H}$ and keeps those boundary terms, naturally leading to a quantum input-output formalism. We recast Maxwell's equations as an operator equation for the dual field $\mathit{E}$=$[\mathbf{E},\mathbf{H}]^T$, whose first-order Green operator $g$ propagates the electromagnetic state between surfaces. Symmetries of the Maxwell operator under energy and reciprocal inner products yield the propagation formula, Lorentz reciprocity, and a generalized optical theorem, with minimal vector calculus. Quantizing via a Heisenberg-Langevin approach for absorptive, dispersive media yields two independent quantum noise sources: bulk Langevin operators from material absorption and input-output field operators at the boundary. Expressing the interior field in terms of these operators and the Green propagator yields an exact closed commutation relation $[{\mathit{E}},{\mathit{E}}^\dagger]\propto \mathrm{Im}\,g$, consistent with the fluctuation-dissipation theorem. This identity holds even when dielectrics extend to the boundary, as in waveguide input-output problems, and enables quantum input-output descriptions of complex photonic structures where the Green's function is obtained numerically, extending the framework beyond cavities and waveguides.

quant-ph↗

arXiv2026

Vapor Phase Assembly of Molecular Emitter Crystals for Photonic Integrated Circuits

Organic molecules embedded in an organic matrix exhibit lifetime-limited optical coherence and bright emission at cryogenic temperatures below 3 K. Here we present a simple vapor-phase growth method for synthesizing optically thin DBT-doped anthracene crystals that are compatible with integrated nanophotonics. The crystals are ~200 nm thick with sub-nm surface roughness and a tunable lateral dimension of up to 200 $\mu$m. The molecular transitions remain narrow and spectrally stable, with inhomogeneous broadening below 100 GHz, comparable to DBT in bulk anthracene. The dopant density is tunable up to several hundred molecules per $\mu$m$^2$, ensuring emitters within the near-field of nanophotonic structures. We demonstrate that the crystals can be micropositioned onto integrated photonic devices with the molecular dipole aligned to the optical mode. This approach opens a path toward on-chip single-photon sources and collective many-emitter effects.

quant-ph↗

arXiv2025

Cavity QED with molecular defects coupled to a photonic crystal cavity

We implement permanent spectral tuning to bring lifetime-limited emitters into collective resonance within an integrated photonic cavity. This addresses a fundamental challenge in solid-state cavity QED: combining multiple coherent quantum emitters with scalable nanophotonics. Our hybrid approach decouples emitter synthesis from nanophotonic fabrication using straightforward techniques that make cavity QED broadly accessible. High doping densities allow us to couple several coherent emitters to a single cavity mode, while optically-induced frequency shifting provides long-lived spectral control. By tuning two molecules into resonance, we demonstrate controlled formation of collective quantum states, establishing a scalable platform for many-body cavity QED. This opens pathways toward chemically-designed quantum systems where optical properties are engineered through synthetic chemistry.

quant-ph↗

arXiv2025

Cooperative Effects in Thin Dielectric Layers: Long-Range Dicke Superradiance

The realization and control of collective effects in quantum emitter ensembles have predominantly focused on small, ordered systems, leaving their extension to larger, more complex configurations as a significant challenge. Quantum photonic platforms, with their engineered Green's functions and integration of advanced solid-state quantum emitters, provide opportunities to explore new regimes of light-matter interaction beyond the scope of atomic systems. In this study, we examine the interaction of quantum emitters embedded within a thin dielectric layer. Our results reveal that the guided optical modes of the dielectric layer mediate extended-range interactions between emitters, enabling both total and directional superradiance in arrays spanning several wavelengths. Additionally, the extended interaction range facilitated by the dielectric layer supports Dicke superradiance in regimes where collective effects cannot be obtained in a homogeneous environment. This work uncovers a distinctive interplay between environmental dimensionality and collective quantum dynamics, paving the way for exploring novel many-body quantum optical phenomena in engineered photonic environments.

quant-ph↗

arXiv2024

Coherent spectroscopy of a single Mn-doped InGaAs quantum dot

Doping a self-assembled InGaAs/GaAs quantum dot (QD) with a single Mn atom, a magnetic acceptor impurity, provides a quantum system with discrete energy levels and original spin-dependent optical selection rules, which thus has large potential in quantum photonics, notably as a source of multi-entangled photons. To investigate this potential further, we perform coherent optical spectroscopy under continuous wave excitation of the 3-level V-like system formed in such a Mn-doped QD when charged by a single hole. In spite of a large inhomogeneous broadening of the optical transitions, we demonstrate Autler-Townes splitting both by resonant Raman scattering and by probe absorption spectroscopy for different saturation powers. Analysing these data with a comprehensive model based on optical Bloch equations, we show evidence for quantum interference within the V-like system and assess the pure dephasing rate between the corresponding spin states.

cond-mat.mes-hall↗

arXiv2013

Sparse Signal Recovery from Nonadaptive Linear Measurements

The theory of Compressed Sensing, the emerging sampling paradigm 'that goes against the common wisdom', asserts that 'one can recover signals in Rn from far fewer samples or measurements, if the signal has a sparse representation in some orthonormal basis', from m = O(klogn), k<< n nonadaptive measurements . The accuracy of the recovered signal is 'as good as that attainable with direct knowledge of the k most important coefficients and its locations'. Moreover, a good approximation to those important coefficients is extracted from the measurements by solving a L1 minimization problem viz. Basis Pursuit. 'The nonadaptive measurements have the character of random linear combinations of the basis/frame elements'. The theory has implications which are far reaching and immediately leads to a number of applications in Data Compression,Channel Coding and Data Acquisition. 'The last of these applications suggest that CS could have an enormous impact in areas where conventional hardware design has significant limitations', leading to 'efficient and revolutionary methods of data acquisition and storage in future'. The paper reviews fundamental mathematical ideas pertaining to compressed sensing viz. sparsity, incoherence, reduced isometry property and basis pursuit, exemplified by the sparse recovery of a speech signal and convergence of the L1- minimization algorithm.

cs.IT↗