Contents

In this article, we present a systematic exposition of Bell’s theorem, starting from the assumptions underlying local hidden-variable models and deriving Bell inequalities in a clear and pedagogical manner. We then review the experimental tests that have confirmed violations of these inequalities, highlighting the closure of various loopholes and the key developments that culminated in the 2022 Nobel Prize in Physics. Our goal is to provide readers with a concise yet comprehensive understanding of Bell’s theorem, its conceptual significance, and its lasting impact on quantum foundations and applications.

Structural control of superconductivity in van der Waals materials offers new opportunities beyond conventional tuning via fields or doping. We investigate twist-stacked heterostructures of monolayer NbSe₂ and graphene, fabricated via molecular beam epitaxy with a variety of twist angles. Ultra-low-temperature spectroscopic imaging scanning tunneling microscopy (SI-STM) reveals Bogoliubov quasiparticles within the superconducting gap, with spatial structures modulated by twist angle. Momentum-resolved analysis revealed a mechanism whereby the superconducting gap of NbSe₂ is selectively suppressed at specific wave vectors where the Fermi surfaces of graphene and NbSe₂ overlap. These findings highlight a twist-dependent, momentum-selective mechanism for modulating superconductivity, suggesting a broadly applicable strategy for engineering unconventional superconducting states through heterostructure design.

Study of the axion production process from the decay of strings in the early universe is indispensable for a precise estimation of the relic axion abundance, from which we could give a prediction for the axion dark matter mass. In this article, we review challenges and recent progress of large scale numerical simulations of axion strings.

The aurora is a natural luminous phenomenon observed in the polar regions caused by interaction between precipitating particles and the constituents of the upper atmosphere. Their luminescence contains information about precipitating electrons and the upper atmosphere. It is useful to acquire two-dimensional (2D) aurora images with full spectrum to study auroral physics. The hyperspectral camera for auroral imaging (HySCAI), which can provide auroral images with high wavelength resolution, was developed by combining a high throughput lens spectrometer with EM-CCD camera and space scanning optics using a galvanometer mirror. The HySCAI has been installed at the KEOPS (Kiruna Esrange Optical Platform Site) of the SSC (Swedish Space Corporation) in Kiruna, Sweden to observe the northern lights. The aurora images with full spectrum in the aurora breakup, that occurred on October 20, 2023, were acquired successfully. The hyperspectral images will provide new insights into the mechanism of auroral emission. The data acquired by HySCAI is publicly available through the Data Repository for Auroral Imaging Spectroscopy (DRAIS) at the National Institute for Fusion Science.