Realization of highly isolated stable few-spin systems based on alkaline-earth fermions

Few-level systems consisting of a certain number of spin states have provided the basis of a wide range of cold atom researches.However,more developments are still needed for better preparation of isolated few-spin systems.In this work,we demonstrate a highly nonlinear spin-discriminating(HNSD)method for isolating an arbitrary few-level manifold out of a larger total number of spin ground states in fermionic alkaline-earth atoms.With this method,we realize large and tunable energy shifts for unwanted spin states while inducing negligible shifts for the spin states of interest,which leads to a highly isolated few-spin system under minimal perturbation.Furthermore,the isolated few-spin system exhibits a long lifetime on the hundred-millisecond scale.Using the HNSD method,we demonstrate a characteristic Rabi oscillation between the two states of an isolated two-spin Fermi gas.Our method has wide applicability for realizing long-lived two-spin or high-spin quantum systems based on alkaline-earth fermions.

N-doped carbon shell encapsulated PtZn intermetallic nanopartides as highly efficient catalysts for fuel cells

The high cost and poor durability of Pt nanoparticles(NPs)have always been great challenges to the commercialization of proton exchange membrane fuel cells(PEMFCs).Pt-based intermetallic NPs with a highly ordered structure are considered as promising catalysts for PEMFCs due to their high catalytic activity and stability.Here,we reported a facile method to synthesize N-doped carbon encapsulated PtZn intermetallic(PtZn@NC)NPs via the pyrolysis of Pt@Zn-based zeolitic imidazolate framework-8(Pt@ZIF-8)composites.The catalyst obtained at 800℃(10%-PtZn@NC-800)was found to exhibit a half-wave potential(Ev2)up to 0.912 V versus reversible hydrogen electrode(RHE)for the cathodic oxygen reduction reaction in an acidic medium,which shifted by 26 mV positively compared to the benchmark Pt/C catalyst.Besides,the mass activity and specific activity of 10%-PtZn@NC-800 at 0.9 V versus RHE were nearly 3 and 5 times as great as that of commercial Pt/C,respectively.It is worth noting that the PtZn@NC showed excel Ient stability in oxygen reducti on reacti on(ORR)with just 1 mV of the Ev2 loss after 5,000 cycles,which is superior to that of most reported PtM catalysts(especially those disordered solid solutions).Furthermore,such N-doped carb on shell encapsulated PtZn intermetallic NPs showed significa ntly enha need performances towards the anodic oxidation reaction of organic small molecules(such as methanol and formic acid).The synergistic effects of the N doped carbon encapsulation structure and intermetallic NPs are responsible for outstanding performances of the catalysts.This work provides us a new engineering strategy to acquire highly active and stable multifunctional catalysts for PEMFCs.

二维电磁力的量子精密测量达到10^(-28)牛顿的稳定度

矢量力的高精度测量对基础研究和前沿技术都有着广泛的应用,例如真空波动的探测和纳米结构表面的表征.近几年,由于量子科技的快速发展,交变电磁力的测量已经取得了很大进展,例如利用原子传感器,交流力测量精度已经提高了几个数量级;但是高精度的静态电磁力的测量还亟待提高.本文基于二维光晶格中原子形成的量子物质波,通过倒格矢空间,对静态电磁力进行了精密测量.光晶格将原子实空间的运动和倒空间的动力学分离开,并且提供了校准物质波波矢的基准.光场力和磁场力的测量灵敏度达到2.30(8)×10^(-26) N/√Hz,在两个空间方向上,长期稳定度达到10N量级,实验达到的测量精度可以在1mm的距离感知范德瓦尔斯力.实验进一步运用原子传感器标定了系统中交流电磁力的控制精度.本研究发展的高精度微弱力测量方法为基于原子的力学量子传感技术提供了前所未有的发展空间.

Power-law scalings in weakly-interacting Bose gases at quantum criticality

Weakly interacting quantum systems in low dimensions have been investigated for a long time,but there still remain a number of open questions and a lack of explicit expressions of physical properties of such systems.In this work,we find power-law scalings of thermodynamic observables in low-dimensional interacting Bose gases at quantum criticality.We present a physical picture for these systems with the repulsive interaction strength approaching zero;namely,the competition between the kinetic and interaction energy scales gives rise to power-law scalings with respect to the interaction strength in characteristic thermodynamic observables.This prediction is supported by exact Bethe ansatz solutions in one dimension,demonstrating a simple 1/3-power-law scaling of the critical entropy per particle.Our method also yields results in agreement with a non-perturbative renormalization-group computation in two dimensions.These results provide a new perspective for understanding many-body phenomena induced by weak interactions in quantum gases.