arXiv subjects

Xiaofan Zhou

Publications and source records attributed to Xiaofan Zhou.

34 records · Page 2Linked to original sources

arXiv2024

Invariant representation learning for sequential recommendation

Sequential recommendation involves automatically recommending the next item to users based on their historical item sequence. While most prior research employs RNN or transformer methods to glean information from the item sequence-generating probabilities for each user-item pair and recommending the top items, these approaches often overlook the challenge posed by spurious relationships. This paper specifically addresses these spurious relations. We introduce a novel sequential recommendation framework named Irl4Rec. This framework harnesses invariant learning and employs a new objective that factors in the relationship between spurious variables and adjustment variables during model training. This approach aids in identifying spurious relations. Comparative analyses reveal that our framework outperforms three typical methods, underscoring the effectiveness of our model. Moreover, an ablation study further demonstrates the critical role our model plays in detecting spurious relations.

cs.IR↗

arXiv2023

Magnetic order and strongly-correlated effects in the one-dimensional Ising-Kondo lattice

We investigate the magnetic order and related strongly-correlated effects in an one-dimensional Ising-Kondo lattice with transverse field. This model is the anisotropic limit of the conventional isotropic Kondo lattice model, in the sense that the itinerant electrons interact with the localized magnetic moments via only longitudinal Kondo exchange. Adopting the numerical density-matrix-renormalization group method, we map out the ground-state phase diagram in various parameter spaces. Depending on the Kondo coupling and filling number, three distinct phases, including a metallic paramagnetic, a metallic ferromagnetic, and a gapped spin-density wave phase, are obtained. The spin-density wave is characterized by an ordering wave vector which coincides with the nesting wave vector of the Fermi surface. This makes the corresponding magnetic transition a spin analog of the Peierls transition occurring in the one-dimensional metal. Moreover, by analyzing the momentum distribution function and charge correlation function, the conduction electrons are shown to behave like free spinless fermions in the ferromagnetic phase. We finally discuss the effect of the repulsive Hubbard interaction between conduction electrons. Our work enriches the Kondo physics and deepens the current understanding of the heavy fermion compounds.

cond-mat.str-el↗

arXiv2023

Quantum phases of the biased two-chain-coupled Bose-Hubbard Ladder

We investigate the quantum phases of bosons in a two-chain-coupled ladder. This bosonic ladder is generally in a biased configuration, meaning that the two chains of the ladder can have dramatically different on-site interactions and potential energies. Adopting the numerical density-matrix renormalization-group method, we analyze the phase transitions in various parameter spaces. We find signatures of both insulating-to-superfluid and superfluid-to-insulating quantum phase transitions as the interchain tunnelling is increased. Interestingly, tunning the interaction to some intermediate values, the system can exhibit a reentrant quantum phase transition between insulating and superfluid phases. We show that for infinite interaction bias, the model is amenable to some analytical treatments, whose prediction about the phase boundary is in great agreement with the numerical results. We finally clarify some critical parameters which separate the system into regimes with distinct phase behaviours, and briefly compare typical properties of the biased and unbiased bosonic ladder systems. Our work enriches the Bose-Hubbard physics.

cond-mat.quant-gas↗

arXiv2023

Copy Recurrent Neural Network Structure Network

Electronic Health Record (EHR) coding involves automatically classifying EHRs into diagnostic codes. While most previous research treats this as a multi-label classification task, generating probabilities for each code and selecting those above a certain threshold as labels, these approaches often overlook the challenge of identifying complex diseases. In this study, our focus is on detecting complication diseases within EHRs. We propose a novel coarse-to-fine ICD path generation framework called the Copy Recurrent Neural Network Structure Network (CRNNet), which employs a Path Generator (PG) and a Path Discriminator (PD) for EHR coding. By using RNNs to generate sequential outputs and incorporating a copy module, we efficiently identify complication diseases. Our method achieves a 57.30\% ratio of complex diseases in predictions, outperforming state-of-the-art and previous approaches. Additionally, through an ablation study, we demonstrate that the copy mechanism plays a crucial role in detecting complex diseases.

cs.LG↗

arXiv2023

Spin-tensor Meissner currents of ultracold bosonic gas in an optical lattice

We investigate the Meissner currents of interacting bosons subjected to a staggered artificial gauge field in a three-leg ribbon geometry, realized by spin-tensor--momentum coupled spin-1 atoms in a 1D optical lattice. By calculating the current distributions using the state-of-the-art density-matrix renormalization-group method, we find a rich phase diagram containing interesting Meissner and vortex phases, where the currents are mirror symmetric with respect to the {\color{red}middle leg} (i.e., they flow in the same direction on the two boundary legs opposite to that on the middle leg), leading to the spin-tensor type Meissner currents, which is very different from previously observed chiral edge currents under uniform gauge field. The currents are uniform along each leg in the Meissner phase and form vortex-antivortex pairs in the vortex phase. Besides, the system also support a polarized phase that spontaneously breaks the mirror symmetry, whose ground states are degenerate with currents either uniform or forming vortex-antivortex pairs. We also discuss the experimental schemes for probing these phases. Our work provides useful guidance to ongoing experimental research on synthetic flux ribbons and paves the way for exploring novel many-body phenomena therein.

cond-mat.quant-gas↗

arXiv2023

Exploring interacting topological insulator of extended Su-Schrieffer-Heeger model

Exploring topological phases in interacting systems is a challenging task. We investigate many-body topological physics of interacting fermions in an extended Su-Schrieffer-Heeger (SSH) model, which extends the two sublattices of SSH model into four sublattices and thus is dubbed SSH4 model, based on the density-matrix renormalization-group numerical method. The interaction-driven phase transition from topological insulator to charge density wave (CDW) phase can be identified by analyzing the variations of entanglement spectrum, entanglement entropies, energy gaps, CDW order parameter, and fidelity. We map the global phase diagram of the many-body ground state, which contains nontrivial topological insulator, trivial insulator and CDW phases, respectively. In contrast to interacting SSH model, in which the phase transitions to the CDW phase are argued to be first-order phase transitions, the phase transitions between the CDW phase and topologically trivial/nontrivial phases are shown to be continuous phase transitions. Finally, we {also} show the phase diagram of interacting spinful SSH4 model, where the attractive (repulsive) on-site spin interaction amplifies (suppresses) the CDW phase. The models analyzed here can be implemented with ultracold atoms on optical superlattices.

cond-mat.quant-gas↗

arXiv2022

Markov Decision Process For Automatic Cyber Defense

It is challenging for a security analyst to detect or defend against cyber-attacks. Moreover, traditional defense deployment methods require the security analyst to manually enforce the defenses in the presence of uncertainties about the defense to deploy. As a result, it is essential to develop an automated and resilient defense deployment mechanism to thwart the new generation of attacks. In this paper, we propose a framework based on Markov Decision Process (MDP) and Q-learning to automatically generate optimal defense solutions for networked system states. The framework consists of four phases namely; the model initialization phase, model generation phase, Q-learning phase, and the conclusion phase. The proposed model collects real network information as inputs and then builds them into structural data. We implement a Q-learning process in the model to learn the quality of a defense action in a particular state. To investigate the feasibility of the proposed model, we perform simulation experiments and the result reveals that the model can reduce the risk of network systems from cyber attacks. Furthermore, the experiment shows that the model has shown a certain level of flexibility when different parameters are used for Q-learning.

cs.CR↗

arXiv2020

Synthetic Hall tube of interacting fermions

Motivated by a recent experiment [J. H. Han, et. al., Phys. Rev. Lett.122, 065303 (2019)], we investigate many-body physics of interacting fermions in a synthetic Hall tube, using state-of-the-art density-matrix renormalization-group numerical method. Since the inter-leg couplings of this synthetic Hall tube generate an interesting spin-tensor Zeeman field, exotic topological and magnetic properties occur. Especially, four new quantum phases, such as nontopological spin-vector and -tensor paramagnetic insulators, and topological and nontopological spin-mixed paramagnetic insulators, are predicted by calculating entanglement spectrum, entanglement entropies, energy gaps, and local magnetic orders with 3 spin-vectors and 5 spin-tensors. Moreover, the topologically magnetic phase transitions induced by the interaction as well as the inter-leg couplings are also revealed. Our results pave a new way to explore many-body (topological) states induced by both the spiral spin-vector and -tensor Zeeman fields.

cond-mat.quant-gas↗

arXiv2020

Quantum spiral spin-tensor magnetism

The characterization of quantum magnetism in a large spin ($\geq 1$) system naturally involves both spin-vectors and -tensors. While certain types of spin-vector (e.g., ferromagnetic, spiral) and spin-tensor (e.g., nematic in frustrated lattices) orders have been investigated separately, the coexistence and correlation between them have not been well explored. Here we propose a novel quantum spiral spin-tensor order on a spin-1 Heisenberg chain subject to a spiral spin-tensor Zeeman field, which can be experimentally realized using a Raman-dressed cold atom optical lattice. We develop a method to fully characterize quantum phases of such spiral tensor magnetism with the coexistence of spin-vector and spin-tensor orders as well as their correlations using eight geometric parameters. Our method provides a powerful tool for characterizing spin-1 quantum magnetism and opens an avenue for exploring novel magnetic orders and spin-tensor electronics/atomtronics in large-spin systems.

cond-mat.quant-gas↗

arXiv2018

Rashba and Weyl spin-orbit coupling in an optical lattice clock

Recent experimental realization of one-dimensional (1D) spin-orbit coupling (SOC) for ultracold alkaline-earth(-like) atoms in optical lattice clocks opens a new avenue for exploring exotic quantum matter because of the strongly suppressed heating of atoms from lasers comparing with alkaline atoms. Here we propose a scheme to realize two-dimensional (2D) Rashba and three-dimensional (3D) Weyl types of SOC in a 3D optical lattice clock and explore their topological phases. With 3D Weyl SOC, the system can support topological phases with various numbers as well as types (I or II) of Weyl points. The spin textures of such topological bands for 2D Rashba and 3D Weyl SOC can be detected using suitably designed spectroscopic sequences. Our proposal may pave the way for the experimental realization of robust topological quantum matters and their exotic quasiparticle excitations in ultracold atomic gases.

cond-mat.quant-gas↗

arXiv2018

Magnetic orders in a Fermi gas induced by cavity-field fluctuations

We study magnetic orders of fermions under cavity-assisted Raman couplings in a one-dimensional lattice at half filling. The cavity-enhanced atom-photon coupling introduces a dynamic long-range interaction between the fermions, which competes with the short-range on-site interaction and leads to a variety of magnetic orders. Adopting a numerical density-matrix-renormalization-group method, we investigate the various magnetic orders and map out the steady-state phase diagram. Interestingly, as all the phase transitions take place outside the superradiant regime, the magnetic orders are associated with cavity-field fluctuations with a vanishing number of photons on the mean-field level.

quant-ph↗

arXiv2017

Symmetry-protected topological states for interacting fermions in alkaline-earth-like atoms

We discuss the quantum simulation of symmetry-protected topological (SPT) states for interacting fermions in quasi-one-dimensional gases of alkaline-earth-like atoms such as $^{173}$Yb. Taking advantage of the separation of orbital and nuclear-spin degrees of freedom in these atoms, we consider Raman-assisted spin-orbit couplings in the clock states, which, together with the spin-exchange interactions in the clock-state manifolds, give rise to SPT states for interacting fermions. We numerically investigate the phase diagram of the system, and study the phase transitions between the SPT phase and the symmetry-breaking phases. The interaction-driven topological phase transition can be probed by measuring local density distribution of the topological edge modes.

cond-mat.quant-gas↗

arXiv2017

Interaction-induced exotic vortex states in an optical lattice clock with spin-orbit coupling

Motivated by a recent experiment [L. F. Livi, et al., Phys. Rev. Lett. 117, 220401(2016)], we study the ground-state properties of interacting fermions in a one-dimensional optical lattice clock with spin-orbit coupling. As the electronic and the hyperfine-spin states in the clock-state manifolds can be treated as effective sites along distinct synthetic dimensions, the system can be considered as multiple two-leg ladders with uniform magnetic flux penetrating the plaquettes of each ladder. As the inter-orbital spin-exchange interactions in the clock-state manifolds couple individual ladders together, we show that exotic interaction-induced vortex states emerge in the coupled-ladder system, which compete with existing phases of decoupled ladders and lead to a rich phase diagram. Adopting the density matrix renormalization group approach, we map out the phase diagram, and investigate in detail the currents and the density-density correlations of the various phases. Our results reveal the impact of interactions on spin-orbit coupled systems, and are particularly relevant to the on-going exploration of spin-orbit coupled optical lattice clocks.

cond-mat.quant-gas↗

arXiv2015

Unconventional pairings of spin-orbit coupled attractive degenerate Fermi gas in a one dimensional optical lattice

Understanding novel pairings in attractive degenerate Fermi gases is crucial for exploring rich superfluid physics. In this report, we reveal unconventional pairings induced by spin-orbit coupling (SOC) in a one-dimensional optical lattice, using a state-of-the-art density-matrix renormalization group method. When both bands are partially occupied, we find a strong competition between the interband Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and intraband Bardeen-Cooper-Schrieffer (BCS) pairings. In particular, for the weak and moderate SOC strengths, these two pairings can coexist, giving rise to a new phase called the FFLO-BCS phase, which exhibits a unique three-peak structure in pairing momentum distribution. For the strong SOC strength, the intraband BCS pairing always dominates in the whole parameter regime, including the half filling. We figure out the whole phase diagrams as functions of filling factor, SOC strength, and Zeeman field. Our results are qualitatively different from recent mean-field predictions. Finally, we address that our predictions could be observed in a weaker trapped potential.

cond-mat.quant-gas↗

arXiv2015

Spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical lattice

Motivated by recent experimental development, we investigate spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical lattice. Using the density-matrix renormalization group method, we calculate momentum distribution function, gap, and spin-correlation function to reveal rich ground-state properties. We find that spin-orbit coupling (SOC) can generate unconventional momentum distribution, which depends crucially on the filling. We call the corresponding phase with zero gap the SOC-induced metallic phase. We also show that SOC can drive the system from the antiferromagnetic to ferromagnetic Mott insulators with spin rotating. As a result, a second-order quantum phase transition between the spin-rotating ferromagnetic Mott insulator and the SOC-induced metallic phase is predicted at the strong SOC. Here the spin rotating means that the spin orientations of the nearest-neighbor sites are not parallel or antiparallel, i.e., they have an intersection angle $θ\in (0,π)$. Finally, we show that the momentum $k_{\mathrm{peak}}$, at which peak of the spin-structure factor appears, can also be affected dramatically by SOC. The analytical expression of this momentum with respect to the SOC strength is also derived. It suggests that the predicted spin-rotating ferromagnetic ($k_{\mathrm{peak}% }<π/2$) and antiferromagnetic ($π/2<k_{\mathrm{peak}}<π$) correlations can be detected experimentally by measuring the SOC-dependent spin-structure factor via the time-of-flight imaging.

cond-mat.quant-gas↗

arXiv2012

Extraction of Deep Phylogenetic Signal and Improved Resolution of Evolutionary Events within the recA/RAD51 Phylogeny

The recA/RAD51 gene family encodes a diverse set of recombinase proteins that effect homologous recombination, DNA-repair, and genome stability. The recA gene family is expressed in almost all species of Eubacteria, Archaea, and Eukaryotes, and even in some viruses. To date, efforts to resolve the deep evolutionary origins of this ancient protein family have been hindered, in part, by the high sequence divergence between families (i.e. ~30% identity between paralogous groups). Through (i) large taxon sampling, (ii) the use of a phylogenetic algorithm designed for measuring highly divergent paralogs, and (iii) novel Evolutionary Spatial Dynamics simulation and analytical tools, we obtained a robust, parsimonious and more refined phylogenetic history of the recA/RAD51 superfamily. Taken together, our model for the evolution of recA/RAD51 family provides a better understanding of ancient origin of recA proteins and multiple events leading to the diversification of recA homologs in eukaryotes, including the discovery of additional RAD51 sub-families.

q-bio.GN↗