Artur Czerwinski

In this work, we investigate the application of Machine Learning (ML) algorithms to the identification and quantitative characterization of quantum entanglement in polarization-entangled photon pairs. The analysis is based on simulated symmetric, informationally complete, positive operator-valued measure (SIC-POVM) measurement data, where each two-qubit state is represented by a 16-dimensional measurement vector corresponding to experimentally accessible coincidence counts. The generated SIC-POVM measurement data include Poissonian shot noise. Several supervised ML algorithms, including Logistic Regression, k-Nearest Neighbors, Decision Trees, Support Vector Machines, and Random Forests, are applied to the classification of separable and entangled states directly from raw measurement data, without explicit density matrix reconstruction or the use of conventional separability criteria. The study additionally explores clustering methods and nonlinear regression techniques for estimating continuous entanglement measures. The obtained results demonstrate that ML methods can achieve very high classification accuracy, even under extremely limited training conditions. These findings indicate that ML may provide an efficient alternative to conventional quantum-state analysis under simulated Poissonian noise conditions.

We study quantum coherence in top-antitop production at the LHC by comparing Standard Model predictions with CMS data across different kinematic regimes. Theory and experiment are statistically consistent in the near-threshold and boosted central regions, confirming that the spin-density framework captures the dominant helicity-interference structure. The intermediate-mass window shows a noticeable deviation, indicating enhanced sensitivity to radiative QCD effects. This work reinterprets measured spin-correlation data within a quantum-coherence framework, thereby introducing coherence as a complementary and experimentally grounded probe of the Standard Model spin structure and a potentially sensitive diagnostic of new-physics effects in the top-quark sector.

This paper presents a comprehensive analysis of the link budget for free-space optical systems involving Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) satellites. We develop a detailed model of the satellite-to-ground channel that accounts for the primary physical processes affecting transmittance: atmospheric absorption and scattering, free-space diffraction, and turbulence-induced fluctuations. The study introduces a general method for computing transmittance along a slant path between a satellite and an optical ground station, incorporating zenith angle, slant range, and altitude-dependent attenuation. The proposed framework is intended to support the design and evaluation of space-based optical links and serves as a critical tool for defining technical specifications in satellite communication demonstrators and simulations. Numerical estimates are provided to illustrate the magnitude of losses under typical operational conditions, including the role of aperture averaging. In addition to the link budget analysis, we introduce a satellite-based quantum use case. We propose a scheme for quantum state tomography performed on states generated by an onboard photon source on an LEO or MEO satellite and transmitted to the optical ground station. This approach enables continuous verification of the quality of quantum resources that can be used to perform quantum protocols within quantum information networks.

We present a unified framework for modeling free-space optical (FSO) communication channels under realistic atmospheric conditions, with a focus on both satellite-to-Earth downlinks and horizontal near-ground links. The model accounts for three key factors affecting transmittance: deterministic attenuation from atmospheric absorption and scattering, geometric diffraction losses due to transverse beam broadening, and stochastic intensity fluctuations induced by atmospheric turbulence. For downlink scenarios, we analyze how the ground station altitude influences channel performance, particularly in terms of turbulence-induced variability. Our findings indicate that higher-altitude stations offer enhanced stability of received signals, even when average transmittance remains largely unchanged. The framework is also extended to horizontal FSO links, relevant for inter-city communication. We show that atmospheric effects, including turbulence and attenuation, play a critical role even over moderate distances, emphasizing the importance of realistic modeling for both classical and quantum optical technologies. The results provide practical insight for designing high-fidelity FSO systems, especially in the context of quantum communication, where both loss and stability are essential performance metrics.

The paper [Opt. Express 32, 40150 (2024)] investigates quantum illumination using polarization-entangled photon pairs for object detection in noisy environments. In this comment, we identify errors in the mathematical model for photon loss, particularly in the treatment of quantum entanglement under lossy channels. We show that the claimed robustness of polarization entanglement to photon loss contradicts established principles in quantum information theory, rendering the conclusions on detecting low-reflectivity objects unsupported.

This paper explores the formal structure and philosophical implications of polarization-path entanglement in quantum optics, where different degrees of freedom of a single photon become entangled. We examine the mathematical conditions under which coherence is preserved or lost, emphasizing the role of distinguishability and information flow. The analysis is situated within major interpretational frameworks (including Copenhagen, Many-Worlds, QBism, and Bohmian mechanics) to evaluate whether such entanglement reflects physical reality or epistemic constraints. Finally, we discuss experimental realizations, relevance to quantum information processing, and open conceptual questions regarding the ontological status of single-particle entanglement.

In this study, we analyze the secret key capacity of intensity modulation/direct detection optical key distribution (IM/DD OKD) for a free-space optical (FSO) link between a low-Earth orbit satellite and an optical ground station. Focusing on downlink communication, we account for atmospheric turbulence, which causes random variations in the transmittance of the FSO channel. We implement an atmospheric channel model that accounts for absorption and scattering, geometric losses, pointing errors, and intensity fluctuations. The secret key capacity is quantified under different noise scenarios and reconciliation code efficiencies, assuming a hard decoding scheme. The performance of the IM/DD OKD protocol is compared under direct and reverse reconciliation regimes. Additionally, we examine the impact of weak and strong wind on the strength of atmospheric turbulence, leading to different results of the secret key capacity. Furthermore, we analyze the characteristics of error distributions that arise from protocol optimization. Our results provide insights into optimizing IM/DD OKD protocols for varying atmospheric conditions.