arXiv subjects

Ramniwas Meena

Publications and source records attributed to Ramniwas Meena.

7 recordsLinked to original sources

arXiv2026

A Tutorial on Practical QKD Post-Processing Algorithms Using a GUI-Based Simulation Framework

Recent experimental demonstrations of Quantum Key Distribution (QKD) have attracted significant attention for their ability to establish information-theoretically secure encryption keys for next-generation communication systems. As practical deployment accelerates, the realization of compact, scalable, and high-throughput discrete-variable (DV) QKD systems has become increasingly important. While advances in photonic integration are enabling low-size, low-weight, and low-power QKD hardware, the security and performance of these systems rely heavily on efficient post-processing techniques to generate identical, secure keys. This tutorial presents a comprehensive algorithm-level review of practical post-processing techniques for DV-QKD, with particular emphasis on information reconciliation methods based on Cascade, Winnow, low-density parity-check (LDPC), and polar codes. We also analyze the theoretical asymptotic and finite-size secret key rates (SKRs) of DV-QKD and benchmark these bounds against the practical SKRs achieved using actual post-processing algorithms. Furthermore, we present a server-client model to implement the entire QKD post-processing pipeline. The performance is evaluated in terms of QBER and SKR across various system parameters, considering the complete post-processing pipeline, including sifting, information reconciliation, privacy amplification, and authentication. This tutorial also presents a graphical user interface (GUI) for the QKD post-processing methods, enabling researchers, industry practitioners, and academic users to visualize and analyze the impact of different post-processing techniques and system parameters, such as QBER, on the SKR performance of DV-QKD systems.

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arXiv2026

Performance Analysis of Multiparty GHZ-State Quantum Conference Key Agreement over Optical Fiber Channel

Quantum conference key agreement (QCKA) enables multiple spatially separated users to establish a common key with composable information-theoretic security by exploiting multipartite quantum correlations. Greenberger--Horne--Zeilinger (GHZ) states are a natural resource for this task, but their distribution over optical fiber is degraded by transmission loss, polarization decoherence, and detector imperfections. We investigate the finite-key performance of an $N$-party GHZ-based QCKA system using the $N$-BB84 protocol, where each optical link is modeled by extending the bipartite erasure--Pauli channel to incorporate detector dark counts. We characterize the impact of this quantum channel on the shared GHZ state and derive closed-form expressions for the error rates. The analytical results reveal that the local bit-error rate depends only on transmissivity and dark counts, while the global phase-error rate compounds over all $N-1$ links and therefore degrades faster with both distance and the number of parties. These error rates are integrated into a finite-key secret-key-rate (SKR) framework, in which we optimize the parameter-estimation probability via Brent's derivative-free method. Numerical results show that increasing fiber distance and network size reduce the achievable SKR. Furthermore, the optimized parameter-estimation probability consistently increases the SKR and extends the maximum secure distance relative to a fixed-allocation baseline, with comparison to the asymptotic limit quantifying the residual finite-key penalty.

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arXiv2026

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.

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arXiv2025

Husimi phase distribution in non-Gaussian operations

The Husimi phase distribution, an experimentally measurable quantity, is investigated for single-mode and two-mode squeezed vacuum states. The analysis highlights that non-Gaussian operations, i.e., photon subtraction (PS), photon addition (PA) and photon catalysis (PC), are effective tools for localizing phase distribution and enhancing phase robustness in the presence of noise, while PC enhances phase sensitivity but leads to greater delocalization. The work highlights the perspective that combined effects of squeezing, beam splitter transmittance, and environmental interactions must be carefully considered when quantum state engineering protocols are designed and phase properties provide a valuable insight into this endeavour.

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arXiv2024

Dynamics of Quantum Coherence and Non-Classical Correlations in Open Quantum System Coupled to a Squeezed Thermal Bath

We investigate the intricate dynamics of quantum coherence and non-classical correlations in a two-qubit open quantum system coupled to a squeezed thermal reservoir. By exploring the correlations between spatially separated qubits, we unravel the complex interplay between quantum correlations and decoherence induced by the reservoir. Our findings demonstrate that non-classical correlations such as quantum consonance, quantum discord, local quantum uncertainty, and quantum Fisher information are highly sensitive to the collective regime. These insights identify key parameters for optimizing quantum metrology and parameter estimation in systems exposed to environmental interactions. Furthermore, we quantify these quantum correlations in the context of practical applications such as quantum teleportation, using the two metrics viz. maximal teleportation fidelity and fidelity deviation. This work bridges theoretical advancements with real-world applications, offering a comprehensive framework for leveraging quantum resources under the influence of environmental decoherence.

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arXiv2024

Continuous Variable Based Quantum Communication in the Ocean

Continuous Variable-Based Quantum Cryptography (CV-QKD) is an emerging field in quantum information science, offering unprecedented security for communication protocols by harnessing the principles of quantum mechanics. However, ocean environments pose unique challenges to quantum communication due to their distinct properties and characteristics. This work investigates the impact of turbulence on the transmission of Gaussian light beams used in a continuous variable-based quantum key distribution system for underwater quantum communication. The objective is to quantitatively analyze the induced losses and propose methodologies to mitigate their effects. To achieve this, we adopt the widely accepted ABCD matrix formalism, which provides a comprehensive framework for characterizing the propagation of optical beams through different media. Moreover, a numerical simulation framework is developed to assess the resulting losses and evaluate the performance of the proposed system. The implications of these numerical simulation frameworks for the design and optimization of quantum communication systems for oceanic environments are thoroughly discussed.

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arXiv2022

Characterization of Quantumness of non-Gaussian states under the influence of Gaussian channel

The impact of a noisy Gaussian channel on a wide range of non-Gaussian input states is studied in this work. The nonclassical nature of the states, both input and output, is developed by studying the corresponding photon statistics and quasi-probability distributions. It is found that photon addition has more robust quantum mechanical properties as compared to the photon subtraction case. The threshold value of the noise parameter corresponding to the transition from partial negative (W and P ) and zero (Q) to completely positive definite, at the center of phase space, depends not only on the average number of thermal photons in the state, but also on the squeezing parameter. In addition it is observed that the nonclassicality of the kth-number filtrated thermal state could be further enhanced by adding photon(s).

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