Highlights
SPECIAL TOPIC—Technology of magnetic resonance
COVER ARTICLE
2025, 74 (11): 117401.
doi: 10.7498/aps.74.20250271
Abstract +
Quantum sensing utilizes the quantum resources of well-controlled quantum systems to measure small signals with high sensitivity, and has great potential in both fundamental science and concrete applications. Interacting quantum systems have attracted increasing interest in the field of precise measurements, owing to their potential to generate quantum-correlated states and exhibit rich many-body dynamics. These features provide a novel avenue for exploiting quantum resources in sensing applications. Although previous studies have shown that using such systems can improve sensitivity, they mainly focused on measuring individual physical quantities. In experiment, the challenge of using interacting quantum systems to achieve high-precision measurements of multiple physical parameters simultaneously has not been explored to a large extent. In this study, we demonstrate a first realisation of interaction-based multiparameter sensing by using strongly interacting nuclear spins under ultra-low magnetic field conditions. We find that, as the interaction strength among nuclear spins becomes significantly larger than their Larmor frequencies, a different regime emerges where the strongly interacting spins can be simultaneously sensitive to all components of a multidimensional field, such as a three-dimensional magnetic field. Moreover, we observe that the strong interactions between nuclear spins can increase their quantum coherence times to as long as several seconds, thereby improving measurement precision. Our sensor successfully achieves precision measurement of three-dimensional vector magnetic fields with a field sensitivity reaching the order of 10–11 T and an angular resolution as high as 0.2 rad. Importantly, this approach eliminates the need for external reference fields, thereby avoiding calibration errors and technical noise commonly encountered in traditional magnetometry. Experimentally optimized protocol further enhances the sensitivity of the interacting spin-based sensor by up to five orders of magnitude compared with non-interacting or classical schemes. These results demonstrate the enormous potential of interacting spin systems as a powerful platform for high-precision multi-parameter quantum sensing. The techniques developed here pave the way for a new generation of quantum sensors that use intrinsic spin interactions to exceed the traditional sensitivity limits, presenting a promising route toward ultra-sensitive, calibration-free magnetometry in complex environments.
The 90th Anniversary of Acta Physica Sinica
INVITED REVIEW
2025, 74 (11): 112101.
doi: 10.7498/aps.74.20241650
Abstract +
The equation of state (EoS) of nuclear matter is a description of the macroscopic properties of nuclear matter under different thermodynamic conditions or external fields, which is critical for understanding the theory of the strong interaction—quantum chromodynamics (QCD), the nature of nuclei, the dynamics of heavy-ion collisions (HICs), the internal structure of compact stars, the merger of binary neutron stars, and other physical phenomena. Heavy-ion collisions (HICs) are the only method in laboratories to create nuclear matter with extreme conditions such as high temperatures and high densities. HICs at different energy levels offer the possibility to quantitatively study the properties of nuclear matter under diverse thermodynamic conditions. This paper mainly presents the current research status of the EoS of nuclear matter and introduces the fundamental observables in HICs that are sensitive to the EoS, as well as the typical experiments and results used to explore the EoS. The progress in studying the EoS containing strangeness is also described and its possible research directions in the future are also discussed. The status and progress of worldwide heavy-ion accelerators and experimental spectrometers in the high-baryon density region are introduced, including China’s large-scale scientific facilities, i.e HIRFL-CSR and HIAF, as well as the CEE experiment. Additionally, the opportunities and challenges for experimental research on the EoS of nuclear matter in China are discussed.
Abstract +
As pointed out by Nambu-Goldstone theorem, the breaking of continuous symmetry gives rise to massless or gapless bosonic excitations. In superconductors, continuous local U(1) gauge symmetry is broken. The gapless excitation thus created is the collective phase mode of the superconducting order parameter. In 1962, Philip Anderson pointed out that the Coulomb interaction between Cooper pairs lifts this gapless mode to the superconducting plasma frequency. Therefore, in a superconducting fluid there are no bosonic excitations below the binding energy of the Cooper pairs (2Δ). Anderson’s mechanism also implies that the massless photon, which mediates electromagnetic interaction, becomes massive in a superconductor. This mechanism provides a microscopic theory for the dissipationless charge transport (in conjunction with Landau’s criterion for superfluidity) as well as the Meissner effect inside a superconductor. Jumping into particle physics, in 1964 in order to explain why the gauge bosons for electroweak interaction, namely the W±, Z bosons, are massive, Peter Higgs, François Englert, Tom Kibble and colleagues proposed the existence of a field (presently referred to as the Higgs field) in nature. This matter field couples to the massless W±, Z bosons and generates mass via the Higgs mechanism. Due to their conceptual similarities, these two mechanisms are collectively referred to as the Anderson-Higgs mechanism nowadays. In 2013, the scalar excitation of the Higgs field, namely the Higgs boson, was detected at the Large Hadron Collider, providing the final proof for the Higgs hypothesis nearly 50 years after its proposal. The amplitude mode of the superconducting order parameter, which corresponds to the Higgs boson through the above analogy, is referred to as the Higgs mode of a superconductor. Its spectroscopic detection has also remained elusive for nearly half a century. In recent years, the development of ultrafast and nonlinear spectroscopic techniques enabled an effective approach for investigating the Higgs mode of superconductors. In this paper, we will introduce the historical background of the Higgs mode and review the recent developments in its spectroscopy study. We will also discuss the novel perspectives and insights that may be learnt from these studies for future high-temperature superconductivity research.
SPECIAL TOPIC—Technology of magnetic resonance
EDITOR'S SUGGESTION
2025, 74 (11): 117601.
doi: 10.7498/aps.74.20250224
Abstract +
High-pressure extreme conditions are crucial for realizing novel states and regulating material properties, while magnetic resonance technology is a widely used method to characterize microscopic magnetic structures and magnetic properties. The integration of these two fields offers new opportunities for cutting-edge research in condensed matter physics and materials science. However, conventional magnetic resonance is limited by several factors, such as low spin polarization and low signal detection efficiency, which makes in-situ measurement of micrometer-sized samples under ultra-high pressure a challenge. Recent advances in quantum sensing with color centers in solids, in particular, the development of quantum sensors based on nitrogen vacancy (NV) centers in diamond, provide an innovative solution for magnetic resonance and in-situ quantum sensing under high pressure. This article summarizes the effects of high-pressure conditions on the spin and optical properties, as well as on the magnetic resonance of diamond NV centers. In addition, this article reviews recent advances in high-pressure quantum sensing through applications such as magnetic imaging, pressure detection, and the study of the superconducting Meissner effect under high pressure.
SPECIAL TOPIC—Technology of magnetic resonance
EDITOR'S SUGGESTION
2025, 74 (11): 118703.
doi: 10.7498/aps.74.20250235
Abstract +
Diffusion-weighted magnetic resonance imaging (DWI) holds significant value in neuroscience and clinical disease diagnosis. The most commonly used single-shot echo-planar imaging (EPI) for DWI is affected by static magnetic field (B0) inhomogeneity and $\rm T_2/T_2^*$ decay, leading to geometric distortion, low signal-to-noise ratio (SNR), etc. To solve these problems, researchers have developed more advanced high-resolution diffusion MRI techniques. This article comprehensively reviews these imaging methods. In the context of echo-planar imaging (EPI), this review covers multi-shot EPI-based DWI techniques, including readout-segmented EPI (RS-EPI), interleaved EPI (iEPI), point spread function-encoded EPI (PSF-EPI), and echo-planar time-resolved imaging (EPTI). These methods effectively reduce or eliminate geometric distortions while improving SNR and spatial resolution. Additionally, the combination of multi-shot EPI with simultaneous multi-slice (SMS) acquisition can shorten scan time, which is also briefly discussed in this article. Compared with EPI, spiral imaging offers higher SNR and sampling efficiency but is more sensitive to B0 inhomogeneity. In the spiral imaging section, we review single-shot spiral DWI and multi-shot spiral DWI, as well as their integration with SMS techniques. This article emphasizes the concepts, acquisition strategies, and reconstruction methods of these imaging techniques. Finally, we discuss the challenges and future directions of high-resolution diffusion imaging, including 3D DWI, body DWI, magnetic field probes, ultra-high gradient systems, and ultra-high-field MRI systems.
EDITOR'S SUGGESTION
2025, 74 (11): 116101.
doi: 10.7498/aps.74.20250368
Abstract +
Amorphous alloys have become a research hotpot in the field of materials science due to their unique long-range disordered structure and excellent physical properties. However, the complex microstructural evolution and electronic transport mechanisms of amorphous alloys under thermal effects still need in depth investigating. In this work, Ni40Fe35B15Si7P3 and Ni50Fe25B15Si7P3 amorphous alloy ribbons are prepared by the melt-spinning technique, and the as-cast samples are subjected to annealing treatments within the supercooled liquid region. The results show that annealing within the supercooled liquid region enhances the short-range order, reduces the free volume, and increases the atomic packing density of the alloys. The volume fractions of the local quasi-crystalline clusters in the annealed samples increase to 26%－34%. Furthermore, the increases in scattering centers and the release of internal stresses induced by the supercooled liquid region annealing lead to an increase in the electrical resistivity of the alloys. Specifically, the resistivity of the Ni40Fe35B15Si7P3 alloy increases from 131.8 μΩ·cm to 217.0 μΩ·cm, a increase of 64.6%. Under an applied magnetic field, the deflection of electron trajectories due to the Lorentz force and the magnetostriction effect further increases the resistivity of the alloys. Additionally, thermal activation releases the bound electrons and enhances their scattering, resulting in an increase in the carrier concentration and a decrease in the carrier mobility of the annealed alloys. This study demonstrates that annealing can effectively control the short-range order and free volume distribution of amorphous alloys, thereby influencing their electronic transport properties. The findings provide an experimental basis for designing high-performance amorphous alloy electronic devices.
EDITOR'S SUGGESTION
2025, 74 (11): 117101.
doi: 10.7498/aps.74.20250152
Abstract +
The preparation technology of powder metallurgy is an important way to prepare Bi2Te3-based bulk materials with excellent mechanical properties and thermoelectric properties. However, the loss of sample orientation during the preparation of powder metallurgy results in low thermoelectric properties of the materials. The development of high-performance Bi2Te3-based thermoelectric materials with strong plate texture and fine grains is the focus of research on high-performance Bi2Te3-based thermoelectric materials. In this paper, a series of p-type Bi2Te3-based materials is prepared by vertical corner extrusion preparation technology. The influences of extrusion temperature on the microstructure and texture characteristics of the material and its influence on the thermoelectric properties of the material are systematically studied. In the vertical corner extrusion process, grains preferentially grow along the minimum resistance direction perpendicular to the pressure, that is, along the extrusion direction, thereby further enhancing the (00l) texture of the original hot-pressed sample; in the direction parallel to the pressure, due to friction with the inner wall of the die in the extrusion process, this frictional resistance will promote the inversion of the grains, so that the grains are arranged in a directional manner to reduce the frictional resistance, thus forming the (110) texture, which is not present in the original hot-pressed sample, in the extruded sample, and finally completing the transition from the hot-pressed sample to the plate texture of the extruded sample. When the extrusion temperature is low, the atomic diffusion rate is low, which limits the dynamic recrystallization of the grain, the grain growth process, and the grain deflection speed. With the increase of the extrusion temperature, these processes can be carried out rapidly, thus forming a more obvious plate texture characteristic. The 773 K extruded sample achieves high orientation factors of F(00l) = 0.51 and F(110) = 0.30 in the directions perpendicular to the pressure and parallel to the pressure, respectively, and the carrier mobility is as high as 345.4 cm2·V–1·s–1 at room temperature, which is comparable to the carrier mobility of the zone melt sample, showing excellent electrical transport performance. The power factor reaches 4.43 mW·m–1·K–2 at room temperature. At the same time, the sum of lattice thermal conductivity and bipolar thermal conductivity of the 773 K extruded sample decreases to a minimum value of 0.78 W·m–1·K–1 at 323 K. Finally, the 773 K extruded sample obtains a maximum ZT value of 1.13 at 323 K, which is nearly 70% higher than that of the hot-pressed sample. This research provides a new way for preparing high-performance strong plate textures and fine-grained Bi2Te3-based thermoelectric materials, and lays an important foundation for fabricating micro thermoelectric devices.
EDITOR'S SUGGESTION
2025, 74 (11): 113202.
doi: 10.7498/aps.74.20250168
Abstract +
Complex multi-body interactions between ions and surrounding charged particles exist in hot and dense plasmas, and they can screen the Coulomb potential between the nucleus and electrons and significantly change the atomic structures and dynamic properties, thereby further affecting macroscopic plasma properties such as radiation opacity and the equation of state. Using the atomic-state-dependent (ASD) screening model, we investigate the photoionization dynamics of Fe25+ ions in hot and dense plasma. The photoionization cross section for all transition channels and total cross sections of n ≤ 2 states for Fe25+ ions are studied in detail, and the low-energy characteristics induced by plasma screening are also investigated. Compared with the classical Debye Hückel model, the ASD model introduces degeneracy effects through inelastic collision processes, resulting in higher plasma density requirements for bound electrons to merge into the continuum. Near the threshold, the photoionization cross section obeys the Wigner threshold law after considering the screening effect. As the energy increases, the cross sections show low-energy characteristics such as shape resonance, Cooper minimum, low-energy enhancement, and Combet-Farnoux minimum, which can significantly increase or reduce the cross section of the corresponding energy region. For example, the low-energy enhancement in the 2p→εs1/2 channel increases the cross section by several orders of magnitude, drastically changing the properties of the photoelectron spectrum. It is significant to study the low-energy characteristics for understanding the physical properties of the photoionization cross section. Fe is an important element in astrophysics. The cross section results in the medium and high energy regions calculated by the ASD model in this work can provide theoretical and data support for investigating hot and dense plasmas in astrophysics and laboratory.
EDITOR'S SUGGESTION
2025, 74 (11): 114206.
doi: 10.7498/aps.74.20250348
Abstract +
SPECIAL TOPIC—Technology of magnetic resonance
EDITOR'S SUGGESTION
2025, 74 (11): 118702.
doi: 10.7498/aps.74.20250325
Abstract +
Transcytolemmal water exchange is a critical process for maintaining cellular homeostasis and function, serving as a potential biological marker for tumor proliferation, prognosis, and cellular states. The use of magnetic resonance imaging (MRI) to measure transcytolemmal water exchange can be traced back to the 1960s, when researchers first measured the residence time of intracellular water molecules in erythrocyte suspensions. Meanwhile, the multi-exponential nature of nuclear magnetic resonance signals in biological tissues was discovered. Studies suggested that transcytolemmal water exchange could be one of the factors explaining this characteristic, marking the beginning of research into measuring transcytolemmal water exchange by using magnetic resonance techniques. After decades of development, the current MRI techniques for measuring transcytolemmal water exchange can be broadly classified into two types: relaxation time based and diffusion based magnetic resonance measurement methods. This review introduces the development of these technologies, and discusses the principles, mathematical/biophysical models, results, and validation of representative methods. Regarding relaxation-based MR techniques, this review systematically organizes MRI methods to quantify transcytolemmal water exchange through chronological developments of three biological substrates: ex vivo cell suspensions, ex vivo biological tissues, and in vivo biological tissues. The modeling section emphasizes two frameworks, including the two-site-exchange model and the three-site-two-exchange shutter-speed model. Regarding diffusion-based MR techniques, this review introduces the research progress of diffusion-encoding and modeling for water exchange measurement. The diffusion-encoding methods are introduced according to single diffusion encoding sequences and the double diffusion encoding sequences. For modeling, it covers three types, including the Kärger model based on the two-component Gaussian diffusion assumption, the modified Kärger model incorporating restricted diffusion effects, and first-order reaction kinetic model. Additionally, comparative studies among different diffusion-based methodologies are also discussed. Finally, this review evaluates their respective clinical applications, advantages, and limitations. The future prospects for technological development in this field are also proposed.
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