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Although the multi-antenna or so-called multiple-input multiple-output (MIMO) transmission has been the enabling technology for the past generations of radio-frequency (RF)-based wireless communication systems, its application to the visible light communication (VLC) still faces a critical challenge as the MIMO spatial multiplexing gain can be hardly attained in VLC channels due to their strong spatial correlation. In this paper, we tackle this problem by deploying the optical intelligent reflecting surface (OIRS) in the environment to boost the capacity of MIMO VLC. Firstly, based on the extremely near-field channel condition in VLC, we propose a new channel model for OIRS-assisted MIMO VLC and reveal its peculiar ``no crosstalk'' property, where the OIRS reflecting elements can be respectively configured to align with one pair of transmitter and receiver antennas without causing crosstalk to each other. Next, we characterize the OIRS-assisted MIMO VLC capacities under different practical power constraints and then proceed to maximize them by jointly optimizing the OIRS element alignment and transmitter emission power. In particular, for optimizing the OIRS element alignment, we propose two algorithms, namely, location-aided interior-point algorithm and log-det-based alternating optimization algorithm, to balance the performance versus complexity trade-off; while the optimal transmitter emission power is derived in closed form. Numerical results are provided, which validate the capacity improvement of OIRS-assisted MIMO VLC against the VLC without OIRS and demonstrate the superior performance of the proposed algorithms compared to baseline schemes., Comment: 30 pages, 7 figures, 3 tables

There has been a growing interest in benchmarking sequential recommendation models and reproducing/improving existing models. For example, Rendle et al. improved matrix factorization models by tuning their parameters and hyperparameters. Petrov and Macdonald developed a more efficient and effective implementation of BERT4Rec, which resolved inconsistencies in performance comparison between BERT4Rec and SASRec in previous works. In particular, BERT4Rec and SASRec share a similar network structure, with the main difference lying in their training objective/loss function. Therefore, we analyzed the advantages and disadvantages of commonly used loss functions in sequential recommendation and proposed an improved loss function that leverages their strengths. We conduct extensive experiments on two influential open-source libraries, and the results demonstrate that our improved loss function significantly enhances the performance of GRU4Rec, SASRec, SR-GNN, and S3Rec models, improving their benchmarks significantly. Furthermore, the improved SASRec benchmark outperforms BERT4Rec on the ML-1M and Beauty datasets and achieves similar results to BERT4Rec on the ML-20M and Steam datasets. We also reproduce the results of the BERT4Rec model on the Beauty dataset. Finally, we provide a comprehensive explanation of the effectiveness of our improved loss function through experiments. Our code is publicly available at https://github.com/Li-fAngyU/sequential_rec.

We introduce the concept of braided noncommutative Poisson bialgebras. The theory of cocycle bicrossproducts for noncommutative Poisson bialgebras is developed. As an application, we solve the extending problem by using some non-abelian cohomology theory., Comment: 44 pages, a noncommutative version is given. Continues arXiv:2112.11977, arXiv:2208.02221, arXiv:2208.08281, and arXiv:2203.15692. arXiv admin note: substantial text overlap with arXiv:2211.05202

Controlling the interplay between localized spins and itinerant electrons at the oxide interfaces can lead to exotic magnetic states. Here we devise SrTiO3/LaTiO3/SrTiO3 heterostructures with varied thickness of the LaTiO3 layer (n monolayers) to investigate the magnetic interactions in the two-dimensional electron gas system. The heterostructures exhibit significant Kondo effect when the LaTiO3 layer is rather thin (n = 2, 10), manifesting the strong interaction between the itinerant electrons and the localized magnetic moments at the interfaces, while the Kondo effect is greatly inhibited when n = 20. Notably, distinct Shubnikov-de Haas oscillations are observed and a nonzero Berry phase of {\pi} is extracted when the LaTiO3 layer is rather thin (n = 2, 10), which is absent in the heterostructure with thicker LaTiO3 layer (n = 20). The observed phenomena are consistently interpreted as a result of sub-band splitting and symmetry breaking due to the interplay between the interfacial Rashba spin-orbit coupling and the magnetic orderings in the heterostructures. Our findings provide a route for exploring and manipulating nontrivial electronic band structures at complex oxide interfaces.

Quantum battery (QB) is the miniature energy storage and release device and plays a crucial role in future quantum technology. Here, an implementation scheme of a QB is proposed on a superconducting circuit which is composed by $N$ coupled transmon qubits and a one-dimensional transmission line resonator. We derive the Hamiltonian of the QB system and investigate its charging performance by considering three decay channels. We find that the presence of the decay channels suppresses the high oscillation of the energy storage process, thereby realizing a stable and powerful QB. In particular, compared with the resonator decay and the qubit relaxation, the qubit dephasing shows a counterintuitive advantage in our QB. We show that the nearest neighbor interaction always have a positive impact on the stable energy and the coupling only significantly influences the maximum charging power in the fully nondegenerate ground state region. We also demonstrate the feasibility of our approach by evaluating the QB performance under experimental parameters., Comment: 10 pages, 7 figures

In condensed-matter physics spin-orbit coupling (SOC) is a fundamental physical interaction, which describes how the electrons' spin couples to their orbital motion. It is the source of a vast variety of fascinating phenomena in solids such as topological phases of matter, quantum spin Hall states, and many other exotic quantum states. Although in most theoretical descriptions of the phenomenon of high-temperature superconductivity SOC has been neglected, including this interaction can, in principle, revise the microscopic picture of superconductivity in these compounds. Not only the interaction leading to Cooper pairing but also the symmetry of the order parameter and the topological character of the involved states can be determined by SOC. Here by preforming energy-, momentum-, and spin-resolved spectroscopy experiments with an unprecedented resolution we demonstrate that while probing the dynamic charge response of the FeSe monolayer on strontium titanate, a prototype two dimensional high-temperature superconductor using slow electrons, the scattering cross-section shows a considerable spin asymmetry. We unravel the origin of the observed spin asymmetry by developing a model in which SOC is taken into consideration. Our analysis indicates that SOC in this two dimensional superconductor is rather strong. We anticipate that such a strong SOC can have several serious consequences on the electronic structures and can lead to the formation of topological states. Moreover, a sizable SOC can compete with other pairing scenarios and is crucial for the mechanism of high-temperature superconductivity., Comment: 15 pages, 4 figures. arXiv admin note: text overlap with arXiv:2210.02058

The discovery of two dimensional Van der Waals materials has opened up several possibilities for designing novel devices. Yet a more promising way of designing exotic heterostutures with improved physical properties is to grow a monolayer of these materials on a substrate. For example, in the field of superconductivity it has been demonstrated that the superconducting transition temperature of a monolayer of FeSe grown on some oxide substrates e.g., strontium titanate (STO) is by far higher than its bulk counterpart. Although the system has been considered as a model system for understanding the phenomenon of high-temperature superconductivity, the physical mechanism responsible for this high transition temperature is still highly under debate. Here using momentum and energy resolved high-resolution electron energy-loss spectroscopy we probe the dynamic charge response of the FeSe/STO(001) system and demonstrate that the frequency- and momentum-dependent dynamic charge response is not compatible with a simple film/substrate model. Our analysis reveals the existence of a depletion region at the interface between this Van der Waals monolayer and the substrate. The presence of the depletion layer, accompanied with a considerably large charge transfer from STO into the FeSe monolayer, leads to a strong renormalization of the STO energy bands and a substantial band bending at the interface. Our results shed light on the electronic complexities of the FeSe/oxide interfaces and pave the way of designing novel low-dimensional high-temperature superconductors through interface engineering. We anticipate that the observed phenomenon is rather general and can take place in many two dimensional Van der Waals monolayers brought in contact with dielectric oxides or semiconducting substrates., Comment: 12 pages, 3 figures

Wigner crystal, as the most fundamental exemplification where the many-body interaction forges the electrons into a solid, experiences an intriguing quantum melting where diverse intermediate phases are predicted to emerge near the quantum critical point. Indications of exotic Wigner orders like bubble phase, liquid-solid phase, and anisotropic Wigner phase have been established by optical or transport measurements. However, the direct visualization of lattice-scale melting order, which is of paramount importance to unequivocally uncover the melting nature, remains challenging and lacking. Noting that Wigner crystals have been achieved in the fractionally filled moire superlattice recently, here, via scanning tunneling microscope, we image the quantum melting of Wigner solid realized by further varying the moire superstructure in monolayer YbCl3/graphene heterostructure. The Wigner solid is constructed on the two-dimensional ensemble of interfacial electron-hole pairs derived from charge transfer. The interplay between certain moire potential and ionic potential leads to the quantum melting of Wigner solid evidenced by the emergence of electron-liquid characteristic, verifying the theoretical predictions. Particularly, akin to the classical quasicrystal made of atoms, a dodecagonal quasicrystal made of electrons, i.e., the Wigner quasicrytal, is visualized at the quantum melting point. In stark contrast to the incompressible Wigner solid, the Wigner quasicrytal hosts considerable liquefied nature unraveled by the interference ripples caused by scattering. By virtue of the two-dimensional charge transfer interface composed of monolayer heavy electron material and graphene, our discovery not only enriches the exploration and understanding of quantum solid-liquid melting, but also paves the way to directly probe the quantum critical order of correlated many-body system.

We introduce the concept of braided alternative bialgebra. The theory of cocycle bicrossproducts for alternative bialgebras is developed. As an application, the extending problem for alternative bialgebra is solved by using some non-abelian cohomology theory., Comment: 61pages, Continues arXiv:2112.11977, arXiv:2203.15692 and arXiv:2208.02221

Let $\mathbb{X}_{\boldsymbol{p},\boldsymbol{\lambda}}$ be a weighted projective line. We define the quantum cluster algebra of $\mathbb{X}_{\boldsymbol{p},\boldsymbol{\lambda}}$ and realize its specialized version as the subquotient of the Hall algebra of $\mathbb{X}_{\boldsymbol{p},\boldsymbol{\lambda}}$ via the quantum cluster character map. Inspired by \cite{Chen2021}, we prove an analogue cluster multiplication formula between quantum cluster characters. As an application, we obtain the polynomial property of the cardinalities of Grassmannian varieties of exceptional coherent sheaves on $\mathbb{X}_{\boldsymbol{p},\boldsymbol{\lambda}}$ . In the end, we construct several bar-invariant $\mathbb{Z}[\nu^{\pm}]$-bases for the quantum cluster algebra of the projective line $\mathbb{P}^1$ and show how it coincides with the quantum cluster algebra of the Kronecker quiver., Comment: 38 pages

With the capability of reconfiguring the wireless electromagnetic environment, intelligent reflecting surface (IRS) is a new paradigm for designing future wireless communication systems. In this paper, we consider optical IRS for improving the performance of visible light communication (VLC) under a multiple-input and multiple-output (MIMO) setting. Specifically, we focus on the downlink communication of an indoor MIMO VLC system and aim to minimize the mean square error (MSE) of demodulated signals at the receiver. To this end, the MIMO channel gain of the IRS-aided VLC is first derived under the point source assumption, based on which the MSE minimization problem is then formulated subject to the emission power constraints. Next, we propose an alternating optimization algorithm, which decomposes the original problem into three subproblems, to iteratively optimize the IRS configuration, the precoding and detection matrices for minimizing the MSE. Moreover, theoretical analysis on the performance of the proposed algorithm in high and low signal-to-noise rate (SNR) regimes is provided, revealing that the joint optimization process can be simplified in such special cases, and the algorithm's convergence property and computational complexity are also discussed. Finally, numerical results show that IRS-aided schemes significantly reduce the MSE as compared to their counterparts without IRS, and the proposed algorithm outperforms other baseline schemes.