arXiv subjects

Ravindra Kumar

Publications and source records attributed to Ravindra Kumar.

10 recordsLinked to original sources

arXiv2026

Purcell enhanced and blinking free single photons from InAs/GaAs quantum dots in deterministically placed circular Bragg gratings

The development of efficient, deterministic, and tunable single-photon sources is a cornerstone for the realization of long-distance quantum communication, quantum repeaters, and photonic quantum computing technologies. In this study, we demonstrate a bright, charge-tunable single-photon source in the 900 nm wavelength range based on InAs quantum dots (QDs) embedded in a p-i-n doped GaAs membrane, which shows blinking free emission. We use a modified circular Bragg grating (CBG) as a micro-resonator. By adding fourfold symmetric bridges in a labyrinth-like geometry, we provide a conductive pathway to the central disk, thereby enabling electrical contact to the QD while maintaining high Purcell enhancement and photon extraction efficiency (PEE). For the negative trion (X-), we demonstrate a lifetime of $44.3 \pm 0.2$ ps - corresponding to a Purcell factor of $18.0 \pm 0.7$ and a PEE of $68.1% \pm 3.1$ %. Furthermore, the device is blinking-free with very low multi-photon contribution, evidenced by a second-order autocorrelation value $g(2)(0) < 0.017 \pm 0.015$. By applying a vertical diode bias, we demonstrate precise charge-state control, resolving distinct emission plateaus ranging from the single negatively charged trion ($X^-$) to triply negatively charged excitons ($X^{3-}$). These results showcase a robust architecture that simultaneously provides high efficiency, high repetition rates, and deterministic charge control, fulfilling key requirements for the next generation of quantum network hardware.

cond-mat.mes-hall↗

arXiv2024

Roman domination number of zero-divisor graphs over commutative rings

For a graph $G= (V, E)$, a Roman dominating function is a map $f : V \rightarrow \{0, 1, 2\}$ satisfies the property that if $f(v) = 0$, then $v$ must have adjacent to at least one vertex $u$ such that $f(u)= 2$. The weight of a Roman dominating function $f$ is the value $f(V)= \Sigma_{u \in V} f(u)$, and the minimum weight of a Roman dominating function on $G$ is called the Roman domination number of $G$, denoted by $\gamma_R(G)$. The main focus of this paper is to study the Roman domination number of zero-divisor graph $\Gamma(R)$ and find the bounds of the Roman domination number of $T(\Gamma(R))$.

math.CO↗

arXiv2018

Pancyclic zero divisor graph over the ring $\mathbb{Z}_n[i]$

Let $\Gamma(\mathbb{Z}_n[i])$ be the zero divisor graph over the ring $\mathbb{Z}_n[i]$. In this article, we study pancyclic properties of $\Gamma(\mathbb{Z}_n[i])$ and $\overline{\Gamma(\mathbb{Z}_n[i])}$ for different $n$. Also, we prove some results in which $L(\Gamma(\mathbb{Z}_n[i]))$ and $\overline{L(\Gamma(\mathbb{Z}_n[i]))}$ to be pancyclic for different values of $n$.

math.CO↗

arXiv2017

Divisor graph of complement of Gamma(R)

Let overline{\Gamma(R)} be the complement of zero divisor graph of a finite commutative ring R. In this article, we have provided the answer of the question (ii) raised by Osba and Alkam in their paper and prove that overline{\Gamma(R)} is a divisor graph if R is a local ring. It is shown that when R is a product of two local rings, then overline{\Gamma(R)} is a divisor graph if one of them is an integral domain. Also, we prove that if cardinality of Ass(R) = 2, then overline{\Gamma(R)} is a divisor graph.

math.CO↗

arXiv2017

Very cost effective bipartition in Gamma(Z_n)

Let Z_n be the finite commutative ring of residue classes modulo n and Gamma(Z_n) be its zero-divisor graph. The nilradical graph and non-nilradical graph of Z_n are denoted by N(Z_n) and Omega(Z_n) respectively. In 2012, Haynes et al. [5] introduced the concept of very cost effective graph. For a graph G = (V,E) and a set of vertices S subset of V, a vertex v in S is said to be very cost effective if it is adjacent to more vertices in V\S than in S. A bipartition Pi = {S, V\S} is called very cost effective if both S and V\S are very cost effective sets [5,6]. In this paper, we investigate the very cost effective bipartition of Gamma(Z_n), where n = p_1 p_2 ... p_m, here all p_i's are distinct primes. In addition, we discuss the cases in which N(Z_n) and Omega(Z_n) graphs have very cost effective bipartition for different n. Finally, we derive some results for very cost effective bipartition of the Line graph and Total graph of Gamma(Z_n), denoted by L(Gamma(Z_n)) and T(Gamma(Z_n)) respectively.

math.CO↗

arXiv2013

Compton Scattering in Plasma: Multiple Scattering Effects and Application to Laser-Plasma Acceleration

We explore the physics of electron acceleration in a plasma medium in an effective field theory framework. Employing a multiple Compton scattering mechanism, it is found that the acceleration can be sustained in such a medium so as to attain the energies up to the order of $O(100 \rm{MeV})$ within a centimeter. Also, the collimation and mono-energetic electron spectrum can be obtained by proper tuning of the plasma parameters with the photon frequency. The present work is potentially useful in understanding the physics of laser-plasma accelerators.

physics.plasm-ph↗

arXiv2011

Collimation and acceleration of mono-energetic electron beams in Laser Plasma accelerators

Motivated by rapid advances in plasma based accelerators, we propose a simple mechanism for the production of highly collimated quasi monochromatic electrons beams. By considering Compton scattering of electrons (in the plasma) with virtual photons -- through an effective interaction --- we demonstrate angular collimation with a divergence less than 3 mrad quasi mono-energetic nature of the beam and an energy gain of O (1 GeV/cm), in laser induced accelerators.

physics.plasm-ph↗

arXiv2008

Hot QCD equations of state and RHIC

We show how hot QCD equations of states can be adapted to make definite predictions for quark-gluon plasma at RHIC. We consider equations of state up to $O(g^5)$ and $O[g^6(ln(1/g)+δ)]$. Our method involves the extraction of equilibrium distribution functions for gluons and quarks from these equations of state by capturing the the interaction effects entirely in the effective chemical potentials. We further utilize these distribution functions to study the screening length in hot QCD and dissociation phenomenon of heavy quarkonia states by combining this understanding with the semi-classical transport theory.

nucl-th↗

arXiv2007

Hot QCD equations of state and relativistic heavy ion collisions

We study two recently proposed equations of state (EOS) which are obtained from high temperature QCD, and show how they can be adapted to use them for making predictions for relativistic heavy ion collisions. The method involves extracting equilibrium distribution functions for quarks and gluons from the EOS, which in turn will allow a determination of the transport and other bulk properties of the quark gluon plasma. Simultaneously, the method also yields a quasi particle description of interacting quarks and gluons. The first EOS is perturbative in the QCD coupling constant and has contributions of $O(g^5)$. The second EOS is an improvement over the first, with contributions upto $ O(g^6 ln(\frac{1}{g}))$; it incorporates the nonperturbative hard thermal contributions. The interaction effects are shown to be captured entirely by the effective chemical potentials for the gluons and the quarks, in both the cases. The chemical potential is seen to be highly sensitive to the EOS. As an application, we determine the screening lengths which are, indeed the most important diagnostics for QGP. The screening lengths are seen to behave drastically differently depending on the EOS considered., and yield, therefore, a way to distinguish the two equations of state in heavy ion collisions.

nucl-th↗

arXiv2007

Chromo-electric Yang-Mills gauge fields

We obtain static gauge field configurations for SU(2) Yang-Mills gauge theory in the absence of chromo-magnetic field. We also present a systematic way to obtain such configurations for SU(3) and SU(4) YM gauge theories by realizing their Lie algebras in terms of SU(2). Generalization of our method to SU(N) gauge theory with N>2 is straight forward. The gauge fields thus obtained are complex. We investigated the issue of uniform as well as real chromo-electric field with these configurations. Furthermore, we investigated the possible class of vacuum solutions for the gauge fields and found that they are gauge inequivalent to the usual vacuum configuration $A^a_μ=0$.

hep-th↗