We investigate the impurity problem of a highly polarized Fermi gas with periodically modulated atom-atom interactions. We find that generalized time-periodic Floquet polaron and molecule emerge as quasistationary quasiparticle states of the system, which exhibit peculiar features distinct from those in a static system. Even in the high-frequency limit, the periodic driving can renormalize the scattering length of the static (effective) Hamiltonian and thus modify the polaron-to-molecule transition. Remarkably, due to the folding of the quasienergy of the Floquet states in the Floquet Brillouin zone, unusual energy-level crossings beyond the conventional polaron-to-molecule transition occur. In particular, when the driving frequency is in resonance with the quasienergy difference, both branches of the Floquet polaron can intersect with the molecular state or even themselves under weak driving. The unique physics of these Floquet impurity states is further characterized and elucidated by the experimentally measurable spectral functions and the radio-frequency spectra. Our results pave a way to explore the intriguing nonequililbrium impurity physics beyond a static system via “Floquet engineering.”

Photo-assisted catalytic oxidation is a promising and sustainable method for the formaldehyde (HCHO) degradation. Catalyst loading and surface adsorbed oxygen species are common strategies to enhance the efficiency of photo-assisted catalytic oxidation. In this work, acid-treated zeolite-based natural zeolites (mordenite and stellerite) were used as supports, to obtain Co3O4-natural zeolite composites by impregnation and MOF-templated methods. Under the combined action of visible light irradiation and heat condition, the photo-assisted thermal catalytic performance of different composites was determined. Among these composites, the Co-AS (Co3O4-acidtreated stellerite) composite exhibited the best HCHO mineralization performance. The use of acid-treated stellerite as a catalyst carrier effectively reduced the crystallite size of Co3O4, improved its dispersibility, and increased the surface adsorbed oxygen species, contributing to enhanced catalytic efficiency. The in-situ DRIFTs results showed that the main intermediates of photo-assisted thermal catalysis degradation were dioxymethylene (DOM) and HCOO-. Additionally, the reusability performance of the composites was also investigated. Experimental results showed that the composite had good photo-assisted thermal catalytic performance and durability, making it a promising catalyst for indoor air purification.

We investigate the collective dynamics of two-component Bose-Einstein condensates in a double well poten-tial. By taking into account the Lee-Huang-Yang (LHY) correction from quantum fluctuation, we find that the LHY term, though much smaller than the mean field interactions, can significantly change the coherent oscil-lating behaviors of the bosonic Josephson junction in the regime of g12 similar or equal to -root g11g22. Besides the quantitative renormalization to the plasma frequencies of the Josephson oscillations, a series of unexpected nonzero fixed points beyond mean field emerges in the stationary state. More remarkably, unique macroscopic self-trapping states, which are usually absent in the mean field dynamics, can be sustained by the LHY nonlinearity. Our results reveal the nontrivial LHY effect on the Josephson dynamics, which can be tested in the current experiment.

We investigate a fermionic superfluid with Raman-induced spin-orbit coupling immersed in a Bose-Einstein condensate. By minimizing the total free energy, we find that, with moderate repulsive interspecies interaction, a phase separation occurs where the otherwise nontopological uniform phase is divided into two parts: a purely fermionic one and a Bose-Fermi mix characterized by nontrivial topology with the winding number $W=1$. We verify that Majorana zero modes emerge at the phase interfaces by numerical simulations of the coupled Bogoliubov--de Gennes and Gross--Pitaevskii equations in real space. The tunability of the phase interfaces enables a direct manipulation of the predicted Majorana zero modes.

The tea tree (Camellia sinensis [L.] O. Kuntze) is a perennial cash crop, whose tender shoots and young leaves are used in tea production. Tea tree buds that have burst but have not yet been plucked may be damaged by frost, resulting in severe economic losses. And frost disasters in spring bring a serious threat to tea production in China. However, the impacts of frost disasters on tea production are not well evaluated. To address this gap, we quantified temporal and spatial changes of frost risk in the Yuezhou Longjing tea production area, which is China's largest site of green tea production. Accordingly, we developed a new frost risk index based on the percentage of frost-damaged tea buds in relation to all tea buds and its probability. The results showed that elevation was the main factor associated with frost risk. Applying the Mann Kendall test, the effects of elevation on the tea frost risk in plain areas (50-250 m) and hilly areas (251-450 m) were determined. In plain areas, the frost risks and trends for the percentage of all frost-damaged tea buds did not change significantly with elevation. In hilly areas, the frost risks increased significantly with the increasing of elevations. However, the temporal change of percentage of frost-damaged tea buds decreased significantly, and this change showed a significant decreasing trend with increasing elevation in hilly areas. This trend is conducive to tea production in the hills, which are the main Longjing tea production areas. Our findings provide a better understanding of frost risk in tea production and could offer valuable references for frost risk prevention in tea production.

光辐射计量基标准是国家计量体系的重要组成部分,是相关量值的溯源源头.光辐射计量正在朝着量值复现量子化、计量基标准量值传递扁平化方向发展. 根据发展趋势,中国计量科学研究院牵头承担了国家重点研发计划"光辐射计量基标准研究"项目(项目编号:2016YFF0200300),在光辐射计量基标准体系中的波长、功率以及它们与时间、空间量组合的量值方面开展研究.项目研究了光辐射测量量子化技术、高稳定度激光波长复现技术、高温固定点黑体辐射技术、光腔衰荡法气体成份测量技术、太赫兹关键参数计量技术.

Northeast China (NEC), an important maize region located at high northern latitudes, is undergoing pronounced climate warming. This warming highlights the importance of taking the effects of brief extreme high and low temperature events into account when addressing the impacts of climate warming on crop yields. The spatiotemporal variability of heat and cold stress and their impact on yield were determined by combining climate data, maize phenological observations and yield records from 1981 to 2018 for 17 counties in the major maize cropping area of NEC. Spatially, more severe heat stress during the vegetative phase occurred in the western border and cold stress occurred in the central regions. Both stresses during the reproductive phase and growing degree days (GDD) showed a northeast–southwest gradient. Temporally, we found overall increased (0.5 °C•d/yr) heat stress during the vegetative phase, which was predominantly more than five times that during the reproductive phase. The cold stress during the vegetative phase was alleviated by an average of –1.3 °C•d/yr, particularly in the central regions. In contrast, exposure to a cold environment during the reproductive phase was intensified, with an average of 0.3 °C•d/yr, though a few downward trends mainly occurred near the borders of three provinces. The increasing trend in GDDr was 3.6 °C•d/yr, almost twice as high as that in the vegetative phase. The impact of increased heat stress contributed an average yield loss of 0.10 t/ha/10a, while reduced cold stress during the vegetative phase coupled with increased GDD increased yield by 0.42 t/ha/10a. Although cold stress during the reproductive phase had an insignificant impact on yield, its intensity together with the increase in heat stress, especially in the vegetative phase, should be considered when developing appropriate adaptations to increase maize yield in the face of ongoing warming.

The MODIS 8-day composite evapotranspiration (ET) product (MOD16A2) is widely used to study large-scale hydrological cycle and energy budgets. However, the MOD16A2 spatial resolution (500 m) is too coarse for local and regional water resource management in agricultural applications. In this study, we propose a Deep Neural Network (DNN)-based MOD16A2 downscaling approach to generate 30 m ET using Landsat 8 surface reflectance and temperature and AgERA5 meteorological variables. The model was trained at a 500 m resolution using the MOD16A2 ET as reference and applied to the Landsat 8 30 m resolution. The approach was tested on 15 Landsat 8 images over three agricultural study sites in the United States and compared with the classical random forest regression model that has been often used for ET downscaling. All evaluation sample sets applied to the DNN regression model had higher R2 and lower root-mean-square deviations (RMSD) and relative RMSD (rRMSD) (the average values: 0.67, 2.63 mm/8d and 14.25%, respectively) than the random forest model (0.64, 2.76 mm/8d and 14.92%, respectively). Spatial improvement was visually evident both in the DNN and the random forest downscaled 30 m ET maps compared with the 500 m MOD16A2, while the DNN-downscaled ET appeared more consistent with land surface cover variations. Comparison with the in situ ET measurements (AmeriFlux) showed that the DNN-downscaled ET had better accuracy, with R2 of 0.73, RMSD of 5.99 mm/8d and rRMSD of 48.65%, than the MOD16A2 ET (0.65, 7.18 and 50.42%, respectively).

The Jaynes–Cummings model with or without rotating-wave approximation plays a major role to study the interaction between atom and light. We investigate the Jaynes–Cummings model beyond the rotating-wave approximation. Treating the counter-rotating terms as periodic drivings, we solve the model in the extended Floquet space. It is found that the full energy spectrum folded in the quasi-energy bands can be described by an effective Hamiltonian derived in the high-frequency regime. In contrast to the Z 2 symmetry of the original model, the effective Hamiltonian bears an enlarged U (1) symmetry with a unique photon-dependent atom-light detuning and coupling strength. We further analyze the energy spectrum, eigenstate fidelity and mean photon number of the resultant polaritons, which are shown to be in accordance with the numerical simulations in the extended Floquet space up to an ultra-strong coupling regime and are not altered significantly for a finite atom-light detuning. Our results suggest that the effective model provides a good starting point to investigate the rich physics brought by counter-rotating terms in the frame of Floquet theory.

We investigate the superfluidity of a two-component Fermi gas with spin-orbital-angular-momentum coupling (SOAMC). Due to the intricate interplay of SOAMC, two-photon detuning and atom-atom interaction, a family of vortex ground states emerge in a broad parameter regime of the phase diagram, in contrast to the usual case where an external rotation or magnetic field is generally required. More strikingly, an unprecedented vortex state, which breaks the continuous rotational symmetry to a discrete one spontaneously, is predicted to occur. The underlying physics are elucidated and verified by numerical simulations. The unique density distributions of the predicted vortex states enable a direct observation in experiment.

We study the superradiance transition of a two-component three-dimensional Fermi gas interacting with a single-mode light field of Dicke-type coupling. We find that for a noninteracting gas, due to the Fermi blocking, a unique superradiant state with a superradiant outer shell surrounding an inner Fermi sea may appear, and the critical atom-light coupling strength gc to trigger the superradiance approaches root omega cEF /3 even for a vanishing transition frequency between a two-spin state (omega(a) -> 0), in contrast to g(c) root omega(c) omega(a) -> 0 for a bosonic or spin system. When the atom-atom attraction is included, we find that the atomic superfluid would compete with the superradiance directly and both orders cannot coexist, giving rise to an interesting ground-state phase diagram with a tricritical point. The resultant phases and phase transitions are characterized by the unique fluctuation spectrum beyond the mean-field level. We further analyze the effects caused by the decay of the light field, which is inevitable for a possible realization in a cavity with a cold atom system. Our results would be beneficial for the understanding of the interplay between Fermi superfluid and superradiance.

运用变分波函数的方法,研究了处于无自旋费米海中一维自旋轨道耦合杂质形成的极化子的基本性质.研究结果显示:当杂质没有自旋轨道耦合时,极化子态的动量始终是0;当考虑杂质的一维自旋轨道耦合时,极化子态具有有限的动量,并且随着拉曼耦合强度的增大而减小;当塞曼劈裂不为0时,极化子态的动量会随着拉曼耦合强度的增大而降到0.本文研究的模型可以在现有的实验技术下实现,有助于研究极化费米气体中的少体问题.

We investigate the polaron and molecular states of a fermionic atom with one-dimensional spin-orbit coupling (SOC) coupled to a three-dimensional spinless Fermi sea. Because of the interplay among the SOC, Raman coupling and spin-selected interatomic interactions, the polaron state induced by the spin-orbit coupled impurity exhibits quite unique features. We find that the energy dispersion of the polaron generally has a double-minimum structure, which results in a finite center-of-mass (c.m.) momentum in the ground state, different from the zero-momentum polarons where SOC are introduced into the majority atoms. By further tuning the parameters such as the atomic interaction strength, a discontinuous transition between the polarons with different c.m. momenta may occur, signaled by the singular behavior of the quasiparticle residue and effective mass of the polaron. Meanwhile, the molecular state as well as the polaron-to-molecule transition is also strongly affected by the Raman coupling and the effective Zeeman field, which are introduced by the lasers generating SOC on the impurity atom. We also discuss the effects of a more general spin-dependent interaction and mass ratio. These results would be beneficial for the study of impurity physics brought by SOC.

Terahertz time-domain spectroscopy (THz-TDS) technology is widely used in many fields such as material composition identification, explosive detection, drug and drug composition analysis, and medical diagnosis. The traditional THzTDS uses a Ti; sapphire femtosecond laser as a light source, which is bulky and costly, and limits the large-scale application of THz-TDS. Using a fiber femtosecond laser combined with a fiber-coupled terahertz photoconductive antenna, the THz-TDS system can be designed to be very compact and flexible, while eliminating the need for a free-space optical path, greatly reducing the number of optical mounts The influence of external environment on the signal such as vibration has great application potential in industry and in the field. In this paper, a fiber-type THz-TDS system is designed and developed, and the three subsystems of optics, electricity and software are briefly introduced. The femtosecond pulse width is controlled by fiber dispersion management, so that the femtosecond pulse width of the terahertz photoconductive antenna is kept at about 50 fs, thereby eliminating the terahertz time domain pulse broadening caused by femtosecond pulse broadening. By precisely controlling the polarization state of the femtosecond laser, the polarization direction of the pump laser and the detection laser is kept parallel with the fast or slow axis of the polarization maintaining fiber, thereby eliminating the splitting phenomenon of the terahertz time domain pulse and obtaining the signal to noise ratio. Better than 12 000 single-pulse terahertz time domain waveforms. The variable angle optical path structure design enables easy switching of terahertz transmission spectrum measurement and reflection spectrum measurement, as well as the measurement of variable angle terahertz spectrum.

The prominent Dicke superradiant phase arises from coupling an ensemble of atoms to a cavity optical field when an external optical pumping exceeds a threshold strength. Here we report a prediction of the superradiant instability driven by Anderson localization, realized with a hybrid system of the Dicke and Aubry-André (DAA) model for bosons trapped in a one-dimensional (1D) quasiperiodic optical lattice and coupled to a cavity. Our central finding is that for bosons condensed in a localized phase given by the DAA model, the resonant superradiant scattering is induced, for which the critical optical pumping of the superradiant phase transition approaches zero, giving an instability driven by the Anderson localization. The superradiant phase for the DAA model with or without a mobility edge is investigated, showing that the localization driven superradiant instability is in sharp contrast to the superradiance as widely observed for a Bose-Einstein condensate in extended states, and should be insensitive to the temperature of the system. This study unveils a novel effect of localization on the Dicke superradiance, and is well accessible based on the current experiments.

We investigate the phase diagram of interacting p-orbital Fermi atoms on honeycomb optical lattice. We find that the interatomic interactions play critical roles in such p-orbital systems, which can drive a first-order topological transition from normal phases with trivial topology to topological phases with nonvanishing Chern numbers. Due to the interplay among atomic interactions, the sublattice potential, and the filling factors, the phase diagram of the system exhibits rich phases, which are characterized by Chern numbers and corresponding edge states. Furthermore, the evolution of the band structures and the moving of Dirac cones along with the phase transitions are also discussed.

The Larkin-Ovchinnikov (LO) state which combines the superfluidity and spatial periodicity of pairing order parameters and exhibits supersolid properties has been attracting intense attention in both condensed-matter physics and ultracold atoms. Conventionally, realization of the LO state from an intrinsic s-wave interacting system necessitates breaking the time-reversal (TR) and sometimes spatial-inversion (SI) symmetries. Here we report a prediction that the LO state can be realized in a TR-and SI-symmetric system representing a bilayer Fermi gas subjected to a laser-assisted interlayer tunneling. We show that the intralayer s-wave atomic interaction acts effectively like a p-wave interaction in the pseudospin space. This provides distinctive pairing effects in the present system with pseudspin spin-orbit coupling, and leads to a spontaneous density modulation of the pairing order predicted in a very broad parameter regime. Unlike the conventional schemes, our results do not rely on the spin imbalance or external Zeeman fields, showing a highly feasible way to observe the long-sought-after LO superfluid phase using the laser-assisted bilayer Fermi gases.