Fluorescence thermometry enhanced by the quantum coherence of single spins in diamond

We demonstrate fluorescence thermometry techniques with sensitivities approaching 10 mK⋅Hz^−1/2 based on the spin-dependent photoluminescence of nitrogen vacancy (NV) centers in diamond. These techniques use dynamical decoupling protocols to convert thermally induced shifts in the NV center''s spin resonance frequencies into large changes in its fluorescence. By mitigating interactions with nearby nuclear spins and facilitating selective thermal measurements, these protocols enhance the spin coherence times accessible for thermometry by 45-fold, corresponding to a 7-fold improvement in the NV center’s temperature sensitivity. Moreover, we demonstrate these techniques can be applied over a broad temperature range and in both finite and near-zero magnetic field environments. This versatility suggests that the quantum coherence of single spins could be practically leveraged for sensitive thermometry in a wide variety of biological and microscale systems.     

Superdiffusion of quantized vortices uncovering scaling laws in quantum turbulence

Generic scaling laws, such as Kolmogorov’s 5/3 law, are milestone achievements of turbulence research in classical fluids. For quantum fluids such as atomic Bose–Einstein condensates, superfluid helium, and superfluid neutron stars, turbulence can also exist in the presence of a chaotic tangle of evolving quantized vortex lines. However, due to the lack of suitable experimental tools to directly probe the vortex-tangle motion, so far little is known about possible scaling laws that characterize the velocity correlations and trajectory statistics of the vortices in quantum-fluid turbulence, i.e., quantum turbulence (QT). Acquiring such knowledge could greatly benefit the development of advanced statistical models of QT. Here we report an experiment where a tangle of vortices in superfluid ⁴He are decorated with solidified deuterium tracer particles. Under experimental conditions where these tracers follow the motion of the vortices, we observed an apparent superdiffusion of the vortices. Our analysis shows that this superdiffusion is not due to Lévy flights, i.e., long-distance hops that are known to be responsible for superdiffusion of random walkers. Instead, a previously unknown power-law scaling of the vortex–velocity temporal correlation is uncovered as the cause. This finding may motivate future research on hidden scaling laws in QT.

Quantum fluids, such as superfluids, superconductors, and Bose–Einstein condensates (BECs), exhibit macroscopic quantum coherence that is responsible for their dissipationless motion (1). In these quantum fluids, all rotational motion is sustained by quantized vortex lines, i.e., line-shaped topological defects characterized by a circulating flow of particles with a discrete circulation κ=h/m, where h is Planck’s constant and m is the mass of the particle.Turbulence in quantum fluids, i.e., quantum turbulence (QT), can be induced by a tangle of interacting vortex lines (2). These vortex lines evolve chaotically under their self-induced and mutually induced velocities and can reconnect when they move across each other (3). The underlying science of QT is broadly applicable to a variety of coherent physical systems, such as coherent condensed-matter systems [e.g., superfluid ³He and ⁴He (4), atomic and polariton BECs (5), and type II superconductors (6)], cosmic systems [e.g., neutron-pair superfluid in neutron stars (7, 8), cosmic strings in the Abelian–Higgs model (9), and possible axion dark matter BECs in galactic halos (10)], and even complex light fields (11). Insight into the generic scaling laws that characterize the evolution of quantized vortex tangles can inform statistical models of QT, which could have a broad significance spanning multiple branches of physics.QT research has been conducted mostly in superfluid ³He and ⁴He due to the material’s accessibility and the wide range of length scales involved in their turbulence behaviors (12). Nevertheless, despite extensive theoretical and numerical studies of the vortex-line dynamics in superfluid helium (13–15), past experimental research has largely been limited to the measurements of spatially averaged quantities such as the vortex-line density L (i.e., length of vortices per unit volume) (16–18) or local pressure and temperature variations (19, 20). Important statistical properties of a fully developed vortex tangle, such as the vortex–velocity correlations and their trajectory statistics, remain largely unexplored due to the lack of experimental tools for probing the vortex-line motion.A breakthrough has been made in recent years with the development of quantitative flow visualization techniques (21). In particular, by decorating the vortices in superfluid ⁴He (He II) with solidified hydrogen particles, Bewley et al. (22) demonstrated direct vortex-line visualization. Since then, vortex-line reconnections and Kelvin-wave excitations on individual vortices have been filmed (23–25). Nevertheless, visualization data showing the real-time evolution of a complex vortex tangle are still lacking, which impedes the development of reliable statistical models for describing QT (26).In our recent experiment on He II QT driven by an applied heat current, we seeded the fluid with solidified deuterium (D2) tracer particles and observed that a group of particles could remain trapped on the tangled vortices (27–30). By applying a separation scheme in data analysis (28), we were able to track solely these trapped particles and therefore could directly probe the vortex-tangle dynamics. In this paper, we discuss our study of the apparent diffusion of these trapped particles under experimental conditions where they faithfully follow the motion of the evolving vortices.We report the observation of a superdiffusion of the vortices in the tangle when their root-mean-square displacement (rmsd) is less than the mean intervortex distance ℓ = L−1/2. Surprisingly, our analysis shows that this superdiffusion is not due to Lévy flights (i.e., randomized, long-distance hops) that are known to be responsible for superdiffusion in various physical and nonphysical systems (31). Instead, we reveal that a previously unknown power-law scaling of the vortex–velocity temporal correlation is the cause. The derived power-law exponent appears to be temperature and vortex-line density independent, suggesting that the observed scaling behaviors may be generic properties of a fully developed random vortex tangle. These findings may excite future research on hidden scaling laws in QT.     

Electron spin resonance spectroscopic demonstration of the hydroxyl free radical scavenger properties of dimethylaminoethanol in spin trapping experiments confirming the molecular basis for the biological effects of centrophenoxine

The ADP-Fe(II)-H2O2 system generates OH free radicals which can be trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) thus yielding a measurable signal by electron spin resonance spectroscopy. The amount of DMPO-OH spin adduct formed under certain conditions decreased considerably, if dimethylaminoethanol (DMAE), p-chlorophenoxyacetic acid (PCPA) or centrophenoxine (CPH) were present in comparable concentrations to that of DMPO. It has been demonstrated that such an effect cannot be attributed to any interference of the tested compounds with the Fe(II) and its oxidability by H2O2. The reaction of DMAE with OH free radicals was demonstrated also by using other spin traps. These spin traps reacted with OH free radicals either not at all (phenyl-tert-butylnitrone, PBN) or only to a slight extent (alfa-pyridyl-l-oxide-N-tert-butylnitrone, 4-POBN). DMAE was also a competitive OH free radical scavenger with proline and hydroxyproline, both of which have recently been shown to react with OH free radicals to form nitroxyl free radicals. On the basis of the experimental results, the OH free radical scavenger property of DMAE can be regarded as firmly established. This result supports the molecular mechanism proposed for the explanation of the anti-aging effects of CPH in terms of the membrane hypothesis of aging.     

Optical coherence tomography-derived predictors of stent expansion in calcified lesions

Background

Severe coronary artery calcification is associated with stent underexpansion and subsequent stent failure.

Aims

We aimed to identify optical coherence tomography (OCT)-derived predictors of absolute (minimal stent area [MSA]) and relative stent expansion in calcified lesions.

Methods

This retrospective cohort study included patients who underwent percutaneous coronary intervention (PCI) with OCT assessment before and after stent implantation between May 2008 and April 2022. Pre-PCI OCT was used to assess calcium burden and post-PCI OCT was used to assess absolute and relative stent expansion.

Results

A total of 361 lesions in 336 patients were analyzed. Target lesion calcification (defined as OCT-detected maximum calcium angle ≥ 30°) was present in 242 (67.0%) lesions. Following PCI, median MSA was 5.37 mm² in calcified lesions and 6.24 mm² in noncalcified lesions (p < 0.001). Median stent expansion was 78% in calcified lesions and 83% in noncalcified lesions (p = 0.325). In the subset of calcified lesions, average stent diameter, preprocedural minimal lumen area, and total calcium length were independent predictors of MSA in multivariable analysis (mean difference 2.69 mm²/mm², 0.52 mm²/mm, and −0.28 mm²/5 mm, respectively, all p < 0.001). Total stent length was the only independent predictor of relative stent expansion (mean difference −0.465% per mm, p < 0.001). Calcium angle, thickness, and the presence of nodular calcification were not significantly associated with MSA or stent expansion in multivariable analyses.

Conclusion

Calcium length appeared to be the most important OCT-derived predictor of MSA, whereas stent expansion was mainly determined by total stent length.     

经颅多普勒超声对中枢性眩晕的诊断与前庭功能自旋试验的相关性

目的：探讨经颅多普勒超声对中枢性眩晕的诊断与前庭功能自旋试验的相关性。方法：选择2013年8月至2016年12月在我院接受诊治的86例中枢性眩晕患者作为观察组,同期选择健康志愿者86例作为对照组,两组都进行前庭功能自旋试验与经颅多普勒超声诊断,判断两种方法的相关性。结果：在振幅上,观察组比对照组明显要高(P<0.05),在N1潜伏期上,观察组比对照组明显要低(P<0.05),两组的P1潜伏期和阈值不存在可比性(P>0.05)。同时,观察组的椎动脉与基底动脉血流速度分别为20.44±5.33cm/s和22.48±4.92cm/s,都明显低于对照组的34.28±4.98cm/s和35.20±4.82cm/s(P<0.05)。在观察组中,直线相关分析显示超声椎动脉、基底动脉血流速度与前庭功能 自旋试验中的振幅都呈现明显负相关(P<0.05),与N1潜伏期呈现明显正相关(P<0.05),而与阈值与P1潜伏期无明显相关性(P>0.05)。结论：经颅多普勒超声对中枢性眩晕的诊断与前庭功能自旋试验有很好的相关性,前庭功能自旋试验有助于病灶定位,经颅多普勒超声反映了中枢系统局部血液异常情况     

Freeze-drying of hemoglobin solutions without adjuvant and in presence of glucose,tris, and β-alanine: A study by electron spin resonance of the oxidized compounds produced

Hemoglobin cannot be freeze-dried without the presence of protective compounds. Carbohydrates are a well-known example of such compounds, but we have shown that some amine buffers and amino acids are also very effective. The mechanism of action of all these molecules is unknown. We report here experimental data showing that the protective effect is not the result of a direct bond between iron and the protective compound added.     

Emergence of electron coherence and two-color all-optical switching in MoS2 based on spatial self-phase modulation

Generating electron coherence in quantum materials is essential in optimal control of many-body interactions and correlations. In a multidomain system this signifies nonlocal coherence and emergence of collective phenomena, particularly in layered 2D quantum materials possessing novel electronic structures and high carrier mobilities. Here we report nonlocal ac electron coherence induced in dispersed MoS₂ flake domains, using coherent spatial self-phase modulation (SSPM). The gap-dependent nonlinear dielectric susceptibility χ⁽³⁾ measured is surprisingly large, where direct interband transition and two-photon SSPM are responsible for excitations above and below the bandgap, respectively. A wind-chime model is proposed to account for the emergence of the ac electron coherence. Furthermore, all-optical switching is achieved based on SSPM, especially with two-color intraband coherence, demonstrating that electron coherence generation is a ubiquitous property of layered quantum materials.Recently 2D layered quantum materials have attracted tremendous interest since the discovery of graphene a decade ago (1). Various layered materials, ranging from boron nitride sheets to transition metal dichalcogenides and from topological insulators to high-temperature superconductors, have been intensively investigated (2–11). Strict 2D atomic crystals can now be produced at a macroscopic scale, using a variety of methods (11, 12). Among them molybdenum disulfide (MoS₂) and related layered quantum materials are particularly interesting due to their novel optical properties and potential valleytronics applications (4, 5, 8, 9) at a thickness of monolayer and few layers (2, 10, 13). Layered materials share common physical properties rooted in their ubiquitous 2D quantum nature, for which achieving pure coherence among electrons (lattices) is of particular interest (14–19). The presence of multiple domains is ubiquitous in many known 2D quantum materials, ranging from stripe-order cuprate superconductors to polycrystalline strongly correlated systems. For example, phase locking between different layers of stripe orders is crucial for enhancing the superconducting phase in layered high-temperature superconductors (20, 21).In this work we demonstrate unambiguously that nonlocal and intraband ac electron coherence, of which the electronic wave function oscillates at an optical frequency of 10¹⁴ Hz, can be generated in separate MoS₂ flakes, using spatial self-phase modulation (SSPM). The SSPM is a coherent third-order nonlinear optical process systematically investigated decades ago (22), where the nonlinear optical susceptibility χ⁽³⁾ is uniquely determined by the laser-intensity-dependent refractive index n = n₀ + n₂I, where n₀ and n₂ are linear and nonlinear refractive indexes, respectively. If this effect is strong enough in a material, the phenomenon of self-focusing can be directly observed. The SSPM is also frequently referred to as the optical Kerr effect or the ac Kerr effect (note the difference from the regular Kerr effect). It is parallel to the other third-order nonlinear optical processes, such as third harmonic generation (THG) and four-wave mixing (FWM).Our investigations show that gap-dependent SSPM is a general method for inducing electron coherence in 2D layered materials. Monolayer and few-layer MoS₂ (and other similar layered materials) have finite bandgaps, which lift the obstacle to versatile electronic and optical applications (2, 23, 24). Because SSPM using below-gap photons has not been reported, MoS₂ provides an ideal test platform for observing SSPM in finite-bandgap materials. A model has been developed to account for the coherence emergence process and theoretical calculations have been carried out to unravel the underlying mechanism. Moreover, we demonstrate all-optical switching based on SSPM, which employs intraband electron coherence. This optical switch has multiple advantages, including weak-control-strong performance, cascade-possible, and high-contrast two-color switching.     

Difference in plaque characteristics of coronary culprit lesions in a cohort of Egyptian patients presented with acute coronary syndrome and stable coronary artery disease: An optical coherence tomography study

Aims

This study was designed to utilize frequency-domain optical coherence tomography (FD-OCT) for assessment of plaque characteristics and vulnerability in patients with acute coronary syndrome (ACS) compared to stable coronary artery disease (SCAD).