arXiv subjects

Muskan

Publications and source records attributed to Muskan.

6 recordsLinked to original sources

arXiv2026

Satellite-Based Quantum Communication: Performance Evaluation of Discrete-Variable Quantum Key Distribution Protocols

Quantum Key Distribution (QKD) has emerged as a fundamentally secure approach to communication in the era of quantum computing, offering protection against threats posed to classical cryptographic schemes such as RSA and Diffie-Hellman. This thesis presents a comprehensive performance analysis of satellite-based QKD protocols, focusing on both prepare-and-measure and entanglement-based schemes under realistic atmospheric and operational conditions. The study begins by introducing the theoretical foundations of quantum communication, including qubits, entanglement, and quantum entropy, and motivates the need for satellite-based QKD to overcome the distance limitations of fiber-based systems. Subsequently, the thesis evaluates four prominent QKD protocols-BB84, B92, BBM92, and E91-using a circular beam propagation model that incorporates atmospheric effects such as diffraction, turbulence, attenuation, and pointing errors, along with environmental noise contributions for uplink and downlink. Comparative numerical simulations reveal that protocol performance is strongly influenced by channel asymmetries, beam propagation characteristics, and noise, providing guidance on optimal protocol selection for low Earth orbit (LEO) satellite links. The research further investigates high-dimensional (HD) QKD protocols, specifically HD-BB84 and HD-Extended B92, using the elliptic-beam approximation to account for turbulence-induced distortions for both uplink and downlink. Simulations under vary ing system dimensions, weather conditions, and zenith angles demonstrate that HD-BB84 achieves higher key rates, superior noise tolerance, and more favorable probability distributions of the key rate compared to HD-Extended B92, highlighting the advantages of high-dimensional encoding for robust satellite-based QKD.

quant-ph↗

arXiv2026

Impartial games on two finite Groups

In this paper, we study impartial achievement games and impartial avoidance games introduced by Anderson and Harary. Using the criteria of maximal subgroups, we study the game for Frobenius groups and non-abelian groups with all abelian subgroups.

math.GR↗

arXiv2026

Why is the $d$-Wave spin splitting in CuF$_2$ bulk-like?

With the advent of nonrelativistic spin splitting in collinear compensated antiferromagnets, several candidate materials have also been proposed, among which the family of transition-metal difluorides stands out as a prominent example. Within this family, most members exhibit planar $d$-wave spin splitting, whereas CuF$_2$ shows bulk $d$-wave splitting with an explicit $k_z$ dependence. In this work, we show that this transition from planar to bulk $d$-wave splitting in CuF$_2$ is primarily driven by the antipolar displacements of the F ions, which are absent in the tetragonal rutile structure of the other family members. Our calculations reveal that these additional structural distortions introduce an extra plane of anisotropic magnetization density, giving rise to an additional totally symmetric component of the magnetic octupole tensor. The $k$-space representation of this octupole component, consequently, dictates an additional direction of spin splitting, thereby transforming the $d$-wave spin splitting pattern from planar to bulk-like. We further analyze the effect of spin-orbit coupling on the magnetic octupoles and the resulting spin splitting in the band structure. Our work highlights the possibility of controlling the pattern of nonrelativistic spin splitting through structural modifications, for example, via the application of external pressure.

cond-mat.mtrl-sci↗

arXiv2025

Finite and Asymptotic Key Analysis for CubeSat-Based BB84 QKD with Elliptical Beam Approximation

Satellite and CubeSat-based quantum key distribution (QKD) presents a promising solution for secure long-distance communication by transmitting quantum keys through free space, with CubeSats offering a compact, cost-effective, and scalable platform for deployment. This study investigates the performance of statistical techniques used to compute the finite-block and single-pass secret key lengths (SKL) for weak coherent pulse (WCP)-based efficient BB84 and standard decoy-state BB84 protocols in CubeSat-based systems. An asymptotic key rate analysis is also conducted for both protocols, providing deeper insights into their theoretical performance within the CubeSat context. The channel transmittance is modeled using an elliptical beam approximation, and the key rate performance is evaluated under varying weather conditions for the downlink scenario. The results demonstrate that the efficient BB84 protocol consistently outperforms the standard version across different atmospheric conditions. Furthermore, the probability distribution of key rates (PDR) for both implementations is analyzed, offering a comprehensive evaluation of their practical effectiveness in CubeSat-based QKD applications.

quant-ph↗

arXiv2023

Analysis for satellite-based high-dimensional extended B92 and high-dimensional BB84 quantum key distribution

A systematic analysis of the advantages and challenges associated with the satellite-based implementation of the high dimensional extended B92 (HD-Ext-B92) and high-dimensional BB84 (HD-BB84) protocol is analyzed. The method used earlier for obtaining the key rate for the HD-Ext-B92 is modified here and subsequently the variations of the key rate, probability distribution of key rate (PDR), and quantum bit error rate (QBER) with respect to dimension and noise parameter of a depolarizing channel is studied using the modified key rate equation. Further, the variations of average key rate (per pulse) with zenith angle and link length in different weather conditions in day and night considering extremely low noise for dimension d=32 are investigated using elliptic beam approximation. The effectiveness of the HD-(extended) protocols used here in creating satellite-based quantum key distribution links (both up-link and down-link) is established by appropriately modeling the atmosphere and analyzing the variation of average key rates with the probability distribution of the transmittance (PDT). The analysis performed here has revealed that in higher dimensions, HD-BB84 outperforms HD-Ext-B92 in terms of both key rate and noise tolerance. However, HD-BB84 experiences a more pronounced saturation of QBER in high dimensions.

quant-ph↗

arXiv2023

Performance Analysis of Satellite-Based QKD Protocols

Satellite-based free-space quantum key distribution (QKD) provides a practical framework for achieving secure global communication beyond the limitations of optical fibers. In this work, the quantum bit error rate (QBER) and secure key rate of four representative protocols-BB84, B92, BBM92, and E91 are investigated over low earth orbit (LEO) links in both uplink and downlink configurations. The optical link is modeled using a Gaussian beam formalism, incorporating the effects of diffraction, pointing errors, atmospheric turbulence, and background noise contributions. The protocols are examined under day and night-time operating conditions, and their dependence on the zenith angle is analyzed. The findings show that downlink links generally exhibit lower QBER and higher secure key rates than uplinks, and among prepare-and-measure schemes, BB84 consistently outperforms B92, while in entanglement-based approaches, BBM92 achieves higher key rates than E91.

quant-ph↗