Quantum nanomaterials have been extensively investigated over the past few decades, as these atomic-scale systems exhibit discrete quantum states. Electron spins in both ground and excited states can be exploited to represent quantum information, typically encoded as |0⟩ and |1⟩. In this rapidly advancing field, various quantum states have been explored using a wide range of materials, including superconductors, nitrogen-vacancy centers in diamond, and single-molecule magnets, etc. In this special issue, several recent and significant studies on quantum nanomaterials are reviewed, with a focus on their potential applications in quantum sensing and quantum bits (qubits).

Fault-tolerant quantum computers (FTQCs) are expected to surpass classical computers in solving problems such as integer factorization, quantum chemistry, machine learning, and quantum simulations. Recent progress in quantum error correction, including the realization of logical qubits, has accelerated the transition from noisy intermediate-scale quantum devices (NISQ) toward practical FTQCs. Among various hardware approaches, superconducting qubits and neutral atom qubits are currently leading candidates, with rapid advances reported by major companies and research institutes. However, achieving scalable FTQCs requires overcoming critical technological challenges in materials, device fabrication, and system integration. In this context, surface science and vacuum engineering play pivotal roles. High-quality thin films, defect-free interfaces, ultra-high vacuum environments, and advanced cleaning and bonding techniques directly determine qubit coherence and reliability. This article reviews the current research and business trends in FTQCs and highlights the crucial contributions expected from the surface science and vacuum engineering communities.

The NV center in diamond has been attracting attention from the viewpoint of the application of ultrasensitive sensors and quantum information devices. One of the most significant properties is that the electron spin of the NV center in diamond exhibits the longest spin coherence time at room temperature among solid-state electron spin systems, which is crucial for achieving high sensitivity. This paper describes the basics of diamond-based quantum sensors and our recent research.

Electrons trapped above cryogenic substrates such as liquid helium and solid neon form exceptionally clean physical systems, since they reside in vacuum and are largely isolated from environmental noise. A recent breakthrough has been the realization of charge qubits using electrons on solid neon surfaces, with coherence times reaching T₂ = 2T₁ ≈ 100 µs. In this article, we describe in detail the preparation of cryogenic substrates, electron deposition and the measurement of electron mobility. We further discuss the differences in surface morphology between helium and neon, their impact on mobility and qubit performance, and emphasize the necessity of systematic surface characterization as a means to optimize cryogenic substrate preparation and electron deposition.

The principle of the diamond-scanning nitrogen-vacancy (NV) center probe microscope is introduced, along with our method for fabricating an NV center-containing pillar probe using laser cutting and focused ion beam milling. The NV center probe attached to the apex of a tuning-fork-based atomic force microscope (AFM) enables simultaneous imaging of an AFM topography and an optically detected magnetic resonance signal. Stray magnetic-field detection from magnetic samples and their structures imaging is demonstrated.

We demonstrate spin-polarized scanning tunneling spectroscopy (SP-STS) with high spin resolution, achieved using two types of superconducting tips : a conventional superconducting tip and a Yu-Shiba-Rusinov (YSR) tip, which is created by decorating a single magnetic atom at the apex of a superconducting tip. Owing to their nearly full spin polarization of the density of states, both tips enable quantitative and highly sensitive measurements of the spin polarization of the sample. These techniques provide powerful means for probing emergent quantum phenomena that demand ultrahigh spin sensitivity, including the spin polarization of Majorana zero modes around vortex cores in topological superconductors.

The control of spin information at the atom- or molecule-level is attracting attention for quantum information processing. Scanning tunneling microscopy (STM) can provide a feasibility study for this technique, in which the radio frequency (RF) signal plays a vital role in characterization and operation. In this article, recent studies that combine the RF signal with the STM tunneling junction will be introduced. First, we show an example of electron spin resonance (ESR) detection using STM for a single magnetic molecule adsorbed on a NaCl on Cu. An apparent increase in the tunneling current occurs when the magnetic field and RF parameters satisfy the Zeeman conditions of an unpaired orbital. Second, we analyze how the RF affects scanning tunneling spectroscopy (STS) features, whichc are quasi-particle peaks in the superconducting material. We demonstrated that the STS peak is separated by the photon-assisted tunneling process, which is applicable to a nanoscale chemical analysis.

Freeze-drying is essential for the preservation of biopharmaceuticals and transfusion-ready blood products. However, conventional methods can cause significant cellular damage, leading to hemolysis in red blood cells (RBCs). This study compares the micro powder dry (µPD) method to the slow freeze-drying method to evaluate their effects on RBCs stability. RBCs were freeze-dried using both techniques, and their moisture content and hemolysis rates were measured immediately after drying and again after one month of storage at both refrigerated (2℃) and room temperatures (28℃). The µPD method resulted in lower hemolysis rates immediately after drying compared to the slow method. Furthermore, both moisture content and hemolysis rates showed minimal changes after one month of storage, demonstrating potential for long-term stability. These findings indicate that the µPD method is superior for preserving RBCs, as it effectively minimizes cellular damage during the freeze-drying process.

We report two-dimensional (2D) self-assembled structures of amphiphilic hexabenzocoronene (HBC) derivatives bearing hydrophilic oligo(ethylene glycol) (EG) side chains. Two molecules were studied : HBCGemini, with dodecyl and triethylene glycol (TEG) chains on opposite sides of the HBC core, and HBCTNFGemini, which includes a trinitrofluorenone (TNF) unit at the end of one TEG chain. Scanning tunneling microscopy (STM) revealed distinct 2D structures for both molecules on gold substrates under vacuum. HBCGemini exhibited two patterns - rectangular and square like arrangements - formed through interactions among phenyl groups, TEG chains, and alkyl chains. HBCTNFGemini showed three ordered structures, attributed to dimeric cores formed by interdigitated TEG chains. The flexible EG units adapt to the HBC core and contribute significantly to the self-assembly process through electrostatic and van der Waals interactions.