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Solder joint inspection (SJI) is a critical process in the production of printed circuit boards (PCB). Detection of solder errors during SJI is quite challenging as the solder joints have very small sizes and can take various shapes. In this study, we first show that solders have low feature diversity, and that the SJI can be carried out as a fine-grained image classification task which focuses on hard-to-distinguish object classes. To improve the fine-grained classification accuracy, penalizing confident model predictions by maximizing entropy was found useful in the literature. Inline with this information, we propose using the {\alpha}-skew Jensen-Shannon divergence ({\alpha}-JS) for penalizing the confidence in model predictions. We compare the {\alpha}-JS regularization with both existing entropyregularization based methods and the methods based on attention mechanism, segmentation techniques, transformer models, and specific loss functions for fine-grained image classification tasks. We show that the proposed approach achieves the highest F1-score and competitive accuracy for different models in the finegrained solder joint classification task. Finally, we visualize the activation maps and show that with entropy-regularization, more precise class-discriminative regions are localized, which are also more resilient to noise. Code will be made available here upon acceptance., Comment: Submitted to IEEE Transactions on Components, Packaging and Manufacturing Technology

In this study, the main focus is laid on the design of the optoelectronic quantum illumination system to enhance the system performance, such as operation at high temperature and confinement of the thermally excited photons. The optomechanical based quantum illumination system has wieldy been studied, and the results showed that operation at high temperature is so crucial to preserve the entanglement between modes. The main problem is that the mechanical part has to operate with a low frequency with which a large number of thermally excited photons are generated and worsened the entanglement. To solve this problem, we focus on replacing the mechanical part with the optoelectronic components. In this system, the optical cavity is coupled to the microwave cavity through a Varactor diode excited by a photodetector. The photodetector is excited by the optical cavity modes and drives the current flow as a function of incident light drives the Varactor diode at which the voltage drop is a function of current generated by the photodetector. To engineer the system, the effect of some parameters is investigated. One of the critical parameters is the microwave cavity to the photodetector coupling factor. Our results indicate that this coupling factor induces a significant difference in the new design as compared to the optomechanical quantum illumination system. At some specific values of the coupling factor, the modes remained completely entangled up to 5.5 K and partially entangled around 50 K.

Quantum radar is generally defined as a detection sensor that utilizes the microwave photons like a classical radar. At the same time, it employs quantum phenomena to improve detection, identification, and resolution capabilities. However, the entanglement is so fragile, unstable, and difficult to create and to preserve for a long time. Also, more importantly, the entangled states have a tendency to leak away as a result of noise. The points mentioned above enforces that the entangled states should be carefully studied at each step of the quantum radar detection processes as follows. Firstly, the creation of the entanglement between microwave and optical photons into the tripartite system is realized. Secondly, the entangled microwave photons are intensified. Thirdly, the intensified photons are propagated into the atmosphere (attenuation medium) and reflected from a target. Finally, the backscattered photons are intensified before the detection. At each step, the parameters related to the real mediums and target material can affect the entangled states to leak away easily. In this article, the entanglement behavior of a designed quantum radar is specifically investigated. In this study, the quantum electrodynamics theory is generally utilized to analyze the quantum radar system to define the parameters influencing the entanglement behavior. The tripartite system dynamics of equations of motions are derived using the quantum canonical conjugate method. The results of simulations indicate that the features of the tripartite system and the amplifier are designed in such a way to lead the detected photons to remain entangled with the optical modes.

Entanglement between optical mode and microwave mode is a critical issue in illumination systems. Traditionally, optomechanical systems are applied to couple the optical mode to microcavity modes. However, due to some restrictions of this system such as sensitivity to the thermal noise at room temperature, a novel optoelectronic system is designed in this study to fix the recent system problems. Unlike recent optomechanical systems, the optical modes are directly coupled to the microwave cavity through the optoelectronic elements with no need mechanical system. The main objective of this work is to generate the entangled modes at room temperature. For this purpose, we theoretically analyze the dynamics of motion of the optoelectronic system with the Heisenberg-Langevin equations, from which one can calculate the coupling between optical and microcavity modes. The most important feature of this system is the coupling between optical mode and microwave cavity mode, which is done using a photodetector and a Varactor diode. Hence, by controlling the photodetector current (photocurrent), which is dependent on the optical cavity incidence wave and the Varactor diode biased, which is the function of the photocurrent, the coupling between the optical and microcavity mode is fully done. The modeling results show that the coupled modes are entangled at the room temperature with no need to any mechanical parts.