Quantum annealing of a frustrated magnet.

Quantum annealing, which involves quantum tunnelling among possible solutions, has state-of-the-art applications not only in quickly finding the lowest-energy configuration of a complex system, but also in quantum computing. Here we report a single-crystal study of the frustrated magnet α-CoV2O6, consisting of a triangular arrangement of ferromagnetic Ising spin chains without evident structural disorder. We observe quantum annealing phenomena resulting from time-reversal symmetry breaking in a tiny transverse field. Below ~ 1 K, the system exhibits no indication of approaching the lowest-energy state for at least 15 hours in zero transverse field, but quickly converges towards that configuration with a nearly temperature-independent relaxation time of ~ 10 seconds in a transverse field of ~ 3.5 mK. Our many-body simulations show qualitative agreement with the experimental results, and suggest that a tiny transverse field can profoundly enhance quantum spin fluctuations, triggering rapid quantum annealing process from topological metastable Kosterlitz-Thouless phases, at low temperatures.

Comparative genomics reveals the adaptation of ammonia-oxidising Thaumarchaeota to arid soils.

Thaumarchaeota are predominant in oligotrophic habitats such as deserts and arid soils, but their adaptations to these arid conditions are not well understood. In this study, we assembled 23 Thaumarchaeota genomes from arid and semi-arid soils collected from the Inner Mongolia Steppe and the Qinghai-Tibet Plateau. Using a comparative genomics approach, integrated with 614 Thaumarchaeota genomes from public databases, we identified the traits and evolutionary forces that contribute to their adaptations to aridity. Our results showed that the newly assembled genomes represent an early diverging group within the lineage of ammonia-oxidising Thaumarchaeota. While the genomic functions previously identified in arid soil lineages were conserved across terrestrial, shallow-ocean and deep-ocean lineages, several traits likely contribute to Thaumarchaeota's adaptation to aridity. These include chlorite dismutase, arsenate reductase, V-type ATPase and genes dealing with oxidative stresses. The acquisition and loss of traits at the last common ancestor of arid soil lineages may have facilitated the specialisation of Thaumarchaeota in arid soils. Additionally, the acquisition of unique adaptive traits, such as a urea transporter, Ca2+ :H+ antiporter, mannosyl-3-phosphoglycerate synthase and phosphatase, DNA end-binding protein Ku and phage shock protein A, further distinguishes arid soil Thaumarchaeota. This study provides evidence for the adaptations of Thaumarchaeota to arid soil, enhancing our understanding of the nitrogen and carbon cycling driven by Thaumarchaeota in drylands.

A simulated ecological restoration of bare cut slope reveals the dosage and temporal effects of cement on ecosystem multifunctionality in a mountain ecosystem.

Cement is a critical building material used in the restorations of bare cut slopes. Yet, how cement affects ecosystem's functions and their undertakers remains elusive. Here, we revealed the dosage and temporal effects of cement on plant and soil traits, extracellular enzymes, greenhouse gas fluxes and microbiome using simulation experiments. The results showed that soil pH increased with the cement content at 1st day but relatively constant values around 7 to 7.5 were detected in the flowing days. The ß-1,4-glucosidase, phenol oxidase, leucine aminopeptidase and acid phosphatase showed high activities under high cement content, and they generally increased with the cultivations except for acid phosphatase. CH4 fluxes at 16th day were less than zero, and they increased to peak around at 37th to 44th days followed by decreasing until reaching to relatively stable fluctuations around 0. Despite of decrease patterns, N2O fluxes stayed around zero across the temporal gradient except for the maximum around at 30th day in 2%, 5% and 8% cement treatment. Microbial diversity decreased with the cement content, in which there were a recovery trend for bacteria. By integrating above- and belowground ecosystem traits into a multifunctionality index, we identified a potential optimum cement content (11%). PLSPM showed that multifunctionality was affected by the shifts in soil bacterial community, enzyme activity and greenhouse gases while these components were effected by other environmental changes resulted from cement. Our results demonstrate that cement determines multifunctionality through mediating microbial community and activity, providing new insights for designing in situ experiments and ecological restoration strategies for bare cut slopes.

High accurate self-calibration of photonic integrated circuit using lossless thermo-optic phase shifters.

The accurate calibration of large-scale switch networks is critical for integrated photonics, in which the integrated optical true time delay chip is typical. In this work, a novel self-calibration method without extra testing ports is proposed by introducing lossless thermo-optic phase shifters instead to calibrate the network. As a demonstration, a 5-bit delay line based on silicon nitride is fabricated and calibrated. The extinction ratio of all the switches is greater than 30.9 dB at the cross and bar states. Using this method, the 5-bit optical delay line which can be tuned in a range of 118.53 ps and reach a low delay time deviation less than ±0.4 ps.

Spin Excitation Spectra of Anisotropic Spin-1/2 Triangular Lattice Heisenberg Antiferromagnets.

Investigation of dynamical excitations is difficult but crucial to the understanding of many exotic quantum phenomena discovered in quantum materials. This is particularly true for highly frustrated quantum antiferromagnets whose dynamical properties deviate strongly from theoretical predictions made based on the spin-wave or other approximations. Here, we present a large-scale numerical calculation on the dynamical correlation functions of spin-1/2 triangular Heisenberg model using a state-of-the-art tensor network renormalization group method. The calculated results allow us to gain for the first time a comprehensive picture on the nature of spin excitation spectra in this highly frustrated quantum system. It provides a quantitative account for all the key features of the dynamical spectra disclosed by inelastic neutron scattering measurements for Ba_{3}CoSb_{2}O_{9}, revealing the importance of the interplay between low- and high-energy excitations and its renormalization effect to the low-energy magnon bands and high-energy continuums. We identify the longitudinal Higgs modes in the intermediate-energy scale and predict the energy and momentum dependence of spectral functions along the three principal axes that can be verified by polarized neutron scattering experiments. Furthermore, we find that the spin excitation spectra weakly depend on the anisotropic ratio of the antiferromagnetic interaction.

Interfacial Engineering of Semicoherent Interface at Purified CsPbBr3 Quantum Dots/2D-PbSe for Optimal CO2 Photoreduction Performance.

Heterogeneous photocatalysts are extensively used to achieve interfacial electric fields for acceleration of oriented charge carrier transport and further promotion of photocatalytic redox reactions. Unfortunately, the incoherent interfaces are almost present in the heterostructures owing to large lattice mismatch accompanied by the interfacial defects and high density of gap states, acting as high energy barriers for charge migration. In this work, we report the atomic engineering of CsPbBr3/PbSe heterogeneous interfaces and conversion from incoherent features to semicoherent characters via methyl acetate (MeOAc) purification of CsPbBr3 quantum dots (QDs) before composited with two-dimensional (2D)-PbSe, which is confirmed by high-resolution transmission electron microscopy. The photocatalytic performances and theoretical calculations indicate that semicoherent interfaces are favorable for improving the activity and reactivity of the heterostructure, triggering 3 times enhanced photocatalytic CO2 reduction rate with 91% selectivity and satisfactory stability. This study proposes a facile method for photocatalytic heterojunctions to transform incoherent interfaces to photocatalytically beneficial semicoherent boundaries, accompanying with a systematic analysis of the consequent chemical dynamics to demonstrate the mechanism of the semicoherent interface for supporting photocatalysis. The understandings gained from this work are valuable for rational interfacial lattice engineering of heterogeneous photocatalysts for efficient solar fuel production.

Ultra-low loss SiN edge coupler interfacing with a single-mode fiber.

In this work, an ultra-low loss silicon nitride (SiN) edge coupler was designed and fabricated to interface with a single-mode fiber (SMF). Unlike other works that focus on the core structure, this work focuses on the cladding structure. First, it is demonstrated that the cladding structure ultimately determines the size and shape of the mode when the taper tip width is small enough. Then, the thickness of the up-cladding is optimized to provide enough space for mode expansion in the vertical direction. Air trenches are added to confine the mode laterally. In addition, the refractive index (RI) of the up-cladding layer is slightly increased to prevent light from leaking into the Si substrate. This edge coupler is then fabricated on the SiN platform at Chongqing United Microelectronics Center. For the TE mode at 1630 nm, a coupling loss of 0.67 dB/facet was obtained. At 1550 nm, 0.85 dB/facet and 1.09 dB/facet were measured for the TE and TM modes, respectively, which means that the polarization-dependent loss is 0.24 dB. Although the design method and the structure are based on a pure SiN platform, they are applicable to a silicon-on-insulator platform as well.

The adjustment of life history strategies drives the ecological adaptations of soil microbiota to aridity.

Soil microbiota increase their fitness to local habitats by adjusting their life history strategies. Yet, how such adjustments drive their ecological adaptations in xeric grasslands remains elusive. In this study, shifts in the traits that potentially represent microbial life history strategies were studied along two aridity gradients with different climates using metagenomic and trait-based approaches. The results indicated that resource acquisition (e.g., higher activities of ß-d-glucosidase and N-acetyl-ß-d-glucosidase, higher degradation rates of cellulose and chitin, as well as genes involved in cell motility, biodegradation, transportation and competition) and growth yield (e.g., higher biomass and respiration) strategies were depleted at higher aridity. However, maintenance of cellular and high growth potential (e.g., higher metabolic quotients and genes related to DNA replication, transcription, translation, central carbon metabolism and biosynthesis) and stress tolerance (e.g., genes involved in DNA damage repair, cation transportation, sporulation and osmolyte biosynthesis) strategies were enriched at higher aridity. This implied that microbiota have lower growth yields but are probably well primed for rapid responses to pulses of rainfall in more arid soils, whereas those in less arid soils may have stronger resource acquisition and growth yield abilities. By integrating a large amount of evidence from taxonomic, metagenomic, genomic and biochemical investigations, this study demonstrates that the ecological adaptations of soil microbiota to aridity made by adjusting and optimizing their life history strategies are universal in xeric grasslands and provides an underlying mechanistic understanding of soil microbial responses to climate changes.

Expression and significance of inflammatory reactions mediated by the IL-33/ST2 signaling pathway in the serum of heart failure patients.

OBJECTIVE: This research aimed to explore the clinical significance of inflammatory reactions mediated by the IL-33/ST2 signaling pathway in heart failure (HF) patients. METHODS: A total of 100 HF patients treated in the Department of Cardiology in our hospital were prospectively regarded as the observation group, and 100 healthy age and gender matched patients who were undergoing physical examination were considered as the control group. The levels of interleukin-33 (IL-33), ST2, tumor necrosis factor-α (TNF-α) and pro B-type natriuretic peptide (pro-BNP) in the peripheral blood of patients were detected. The potential correlation between IL-33 and ST2, TNF-α and pro-BNP was analyzed by Pearson. RESULTS: The levels of IL-33, IL-10, ST2 and pro-BNP in the peripheral blood of patients in the observation group were higher than those in the control group; and they increased with the rise of cardiac function grade (all P<0.05). In addition, IL-33 was positively correlated with TNF-α, ST2 and pro-BNP (r=0.863, 0.879, 0.945; all P<0.05). Multivariate Logistic analysis revealed that the increase of IL-33 and ST2 were independent risk factors of HF. CONCLUSION: The IL-33 and ST2 levels in the peripheral serum of HF patients are correlated with TNF-α and BNP, the finding of which can assist in clinical diagnosis and treatment.

Entanglement entropy of non-Hermitian free fermions.

We study the entanglement properties of non-Hermitian free fermionic models with translation symmetry using the correlation matrix technique. Our results show that the entanglement entropy has a logarithmic correction to the area law in both one-dimensional and two-dimensional systems. For any one-dimensional one-band system, we prove that each Fermi point of the system contributes exactly 1/2 to the coefficientcof the logarithmic correction. Moreover, this relation betweencand Fermi point is verified for more general one-dimensional and two-dimensional cases by numerical calculations and finite-size scaling analysis. In addition, we also study the single-particle and density-density correlation functions.

Soil N availability drives the shifts of enzyme activity and microbial phosphorus limitation in the artificial soil on cut slope in southwestern China.

The construction of highways in the subalpine mountains generates many cut slopes. Currently, the restoration of cut slope mainly focuses on the aboveground landscapes and slope stability. Yet, it remains elusive about the belowground ecosystem functions at the early stage of restoration. In this study, we evaluated the belowground ecosystem functions of cut slopes that had been restored approximately 3 years using soil enzymatic activities, microbial biomass, and stoichiometry as the proxies. The results indicated that the phenol oxidase activity was higher in cut slopes, while the activities of ß-1,4-glucosidase, ß-1,4-N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase were lower in cut slope soils compared with natural soils. Soil nitrogen availabilities (total and/or ammonium nitrogen) showed high negative correlations with the phenol oxidase activity and positive correlations with the activities of almost all other enzymes. These results suggested that soil nitrogen was the key factor in driving the shifts of enzymatic activities across two types of soils. Moreover, we found the imbalance of soil nutrients in cut slope soils, especially the carbon vs. nitrogen and the nitrogen vs. phosphorus. By applying the vector analysis, we found that the vector A values were more than 45° in all samples, suggesting that microbial phosphorus limitation occurred in both cut slope and natural soils. These findings suggested that maintaining the balance of soil nutrient supplies is important to the recovery of the below-ground ecosystem functions at the early restoration stage of cut slopes. This study provided new insights into designing the ecological restoration strategies for cut slopes by considering the belowground ecosystem functions.

Critical properties of the two-dimensional q-state clock model.

We perform the state-of-the-art tensor network simulations directly in the thermodynamic limit to clarify the critical properties of the q-state clock model on the square lattice. We determine accurately the two phase transition temperatures through the singularity of the classical analog of the entanglement entropy, and provide extensive numerical evidences to show that both transitions are of the Berezinskii-Kosterlitz-Thouless (BKT) type for q≥5 and that the low-energy physics of this model is well described by the Z_{q}-deformed sine-Gordon theory. We also determine the characteristic conformal parameters, especially the compactification radius, that govern the critical properties of the intermediate BKT phase.

A Distributed and Context-Aware Task Assignment Mechanism for Collaborative Mobile Edge Computing.

Mobile edge computing (MEC) is an emerging technology that leverages computing, storage, and network resources deployed at the proximity of users to offload their delay-sensitive tasks. Various existing facilities including mobile devices with idle resources, vehicles, and MEC servers deployed at base stations or road side units, could act as edges in the network. Since task offloading incurs extra transmission energy consumption and transmission latency, two key questions to be addressed in such an environment are (i) should the workload be offloaded to the edge or computed in terminals? (ii) Which edge, among the available ones, should the task be offloaded to? In this paper, we formulate the task assignment problem as a one-to-many matching game which is a powerful tool for studying the formation of a mutual beneficial relationship between two sets of agents. The main goal of our task assignment mechanism design is to reduce overall energy consumption, while satisfying task owners' heterogeneous delay requirements and supporting good scalability. An intensive simulation is conducted to evaluate the efficiency of our proposed mechanism.

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4.

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ -4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

The form and origin of orbital ordering in the electronic nematic phase of iron-based superconductors.

We investigated the form of orbital ordering in the electronic nematic phase of iron-based superconductors by applying a group theoretical analysis on a realistic five-band model. We find the orbital order can be either of the inter-orbital s-wave form or intra-orbital d-waveform. From the comparison with existing ARPES measurements of band splitting, we find the orbital ordering in the 122 system is dominated by an intra-orbital d-wave component, while that of the 111 system is dominated by an inter-orbital s-wave component. We find both forms of orbital order are strongly entangled with the nematicity in the spin correlation of the system.The condensation energy of the magnetic ordered phase is found to be significantly improved (by more than 20%) when the degeneracy between the (π, 0) and (0, π) ordering pattern is lifted by the orbital order. We argue there should be a large difference in both the scattering rate and the size of the possible pseudogap on the electron pocket around the X = (π, 0) and Y = (0, π) point in the electronic nematic phase. We propose this as a possible origin for the observed nematicity in resistivity measurements.

The Rényi entanglement entropy of a general quantum dimer model at the RK point: a highly efficient algorithm.

A highly efficient and simple-to-implement Monte Carlo algorithm is proposed for the evaluation of the Rényi entanglement entropy (REE) of the quantum dimer model (QDM) at the Rokhsar-Kivelson (RK) point. It makes possible the evaluation of REE at the RK point to the thermodynamic limit for a general QDM. We apply the algorithm to a QDM defined on the triangular and the square lattice in two dimensions and the simple and the face centered cubic (fcc) lattice in three dimensions. We find the REE on all these lattices follows perfect linear scaling in the thermodynamic limit, apart from an even-odd oscillation in the case of the square lattice. We also evaluate the topological entanglement entropy (TEE) with both a subtraction and an extrapolation procedure. We find the QDMs on both the triangular and the fcc lattice exhibit robust Z2 topological order. The expected TEE of ln2 is clearly demonstrated in both cases. Our large scale simulation also proves the recently proposed extrapolation procedure in cylindrical geometry to be a highly reliable way to extract the TEE of a topologically ordered system.

Variational study of the quantum phase transition in the bilayer Heisenberg model with bosonic RVB wavefunction.

We study the ground state phase diagram of the bilayer Heisenberg model on a square lattice with a bosonic resonating valence bond (RVB) wavefunction. The wavefunction has the form of a Gutzwiller projected Schwinger boson mean-field ground state and involves two variational parameters. We find the wavefunction provides an accurate description of the system on both sides of the quantum phase transition. In particular, through the analysis of the spin structure factor, ground state fidelity susceptibility and the Binder moment ratio Q(2), a continuous transition from the antiferromagnetic ordered state to the quantum disordered state is found at the critical coupling of α(c) = J(⊥)/J(∥) ≈ 2.62, in good agreement with the result of quantum Monte Carlo simulation. The critical exponent estimated from the finite size scaling analysis (1/ν ≈ 1.4) is consistent with that of the classical 3D Heisenberg universality class.

Raman spectrum in the pseudogap phase of the underdoped cuprates: effect of phase coherence and the signature of the KT-type superconducting transition.

The temperature evolution of the Raman spectrum of the underdoped cuprates is studied in the thermal phase fluctuation scenario with an XY-type lattice model for the phase degree of freedom. It is found that the pair breaking Raman peak depends sensitively on the phase coherence of the pairing order parameter. As a result, the integrated Raman intensity in both the B(1g) and the B(2g) channels exhibits a dramatic drop across the Kosterlitz-Thouless (KT) transition temperature (T(KT)), when vortex-like phase fluctuation is proliferated. This result, which is consistent with experimental observations, provides further support for the thermal phase fluctuation scenario of the pseudogap phase and the KT-type nature of the superconducting transition in underdoped cuprates.