arXiv subjects

Hoang-Anh Le

Publications and source records attributed to Hoang-Anh Le.

10 recordsLinked to original sources

arXiv2026

Theory of Electron Spin Resonance Scanning Tunneling Microscopy: The First Decade

Electron spin resonance in scanning tunneling microscopy enabled the study of electronic transitions of magnetic impurities on surfaces at the atomic scale. This ESR-STM technique allows to spectroscopically probe and coherently manipulate spins using an all-electrical method without oscillating external magnetic driving fields. Here, we aim to review recent advancements in ESR-STM. We will discuss possible fundamental mechanisms by which the electric field drives spin resonance based on Heisenberg exchange, Kondo scattering, and Anderson impurity models. We validate theoretical predictions against experimental observations, to understand how electronic correlations, spin exchange, and many-body effects manifest in ESR-STM signals. After reviewing coherent spin control in the STM junction, we discuss potential applications of the ESR-STM method for coherent multi-spin control which enables multiple-qubit operations. Finally, we address recent developments in coupled electron-nuclear spin systems, including hyperfine-resolved ESR spectroscopy, and the driving and polarization of nuclear spins in ESR-STM.

cond-mat.mes-hall↗

arXiv2026

Overcoming limitations on gate fidelity in noisy static exchange-coupled surface qubits

Recent experiments demonstrated that the spin state of individual atoms on surfaces can be quantum-coherently controlled through all-electric electron spin resonance. By constructing interacting arrays of atoms this results in an atomic-scale qubit platform. However, the static exchange coupling between qubits, limited lifetime and polarization of the initial state, impose significant limits on high-fidelity quantum control. We address this issue using open quantum systems simulation and quantum optimal control theory. We demonstrate the conditions under which high-fidelity operations ($\mathcal{F} \gtrsim 0.9$) are feasible in this qubit platform, and show how the Krotov method of quantum optimal control theory adapts to specific noise sources to outperform the conventional Rabi drivings. Finally, we re-examine the experimental setup used in the initial demonstration of this qubit platform and propose optimized experimental designs to maximize gate fidelity in this platform.

quant-ph↗

arXiv2026

Quantum Entanglement of Anyonic Charges and Emergent Spacetime Geometry

Intrinsically topologically ordered phases can host anyons. Here, we take the view that entanglement between anyons can give rise to an emergent geometry resembling Anti-de Sitter (AdS) space. We analyze the entanglement structure of fractionalized anyons using mutual information and interpret the results within this emergent geometric framework. As a concrete example, we consider pairs of $e/2$-charged semions that arise from instanton configurations in a disordered zigzag graphene nanoribbon. These fractional charges, located on opposite zigzag edges, show long-range quantum entanglement despite being spatially separated. We analyze the scale dependence of their entanglement and embed the ribbon into an AdS-like bulk geometry. In this setup, the entanglement structure defines minimal surfaces in the bulk, providing a geometric view of the edge correlations. This gives a holographic picture of fractionalized degrees of freedom in quasi-one-dimensional systems and shows how quantum entanglement can generate emergent geometry even without conformal symmetry.

cond-mat.str-el↗

arXiv2025

Efficient driving of a spin-qubit using single-atom magnets

The realization of electron-spin resonance at the single-atom level using scanning tunneling microscopy has opened new avenues for coherent quantum sensing and quantum state manipulation at the ultimate size limit. This allows to build many-body Hamiltonians and the study of their complex physical behavior. Recently, a novel qubit platform has emerged from this field, raising questions about the driving mechanism from single-atom magnets. In this work, we demonstrate how single-atom magnets can be used to drive a nearby single spin qubit efficiently. We show that the modulation of exchange coupling is the primary driving force, which successfully reproduces Rabi rates in the tens of MHz range, consistent with experimental data, while also addressing critical aspects related to the optimization of experimental parameters.

cond-mat.mes-hall↗

arXiv2025

Instantons and topological order in two-leg electron ladders: A universality class

Our numerical study of the disordered Hubbard model with nearest-neighbor hopping shows that a two-leg electron ladder has a finite topological entanglement entropy in the regime where the density of states exhibits an exponentially decaying gap. The value of the topological entanglement entropy suggests that two-leg ladders belong to the same universality class as graphene zigzag nanoribbons, despite several structural differences. A Shankar-Witten-type bosonization Lagrangian with disorder captures several features of the numerically obtained results for disordered two-leg ladders. Additionally, we propose a Lagrangian in which the fusion of two semions residing on different chains generates a fermion (instanton). We apply this Lagrangian within the framework of the pinned charge-density-wave model and compute the relevant Green's function using the bosonization method. This approach predicts a linear density of states at a critical disorder strength. Below this threshold, a soft gap emerges, which is in qualitative agreement with our numerical results.

cond-mat.str-el↗

arXiv2025

The Effects of Trade Openness on CO2 Emission in Vietnam

This paper investigates the relationship between trade openness and CO2 emissions in Vietnam using the data from 1986 to 2014. We examine the consistency of the environmental Kuznets curve hypothesis (EKC) and the pollution heaven hypothesis (PHH) in Vietnam case. In 1986 Vietnam government began to launch free-market economic reforms. Since then, Vietnam economy experienced the breakthrough innovation in trade openness. On the other hand, Vietnam witness a growing level of CO2 emission. The annual growth rate of CO2 emission during the period is 7.26%, and that of trade volume is 16.11%. The empirical results show that the relationship between CO2 emissions and income per capita is an inverted U-shaped, consistent with to EKC hypothesis. We also find that the pollution heaven hypothesis is supported in that energy use and international trade contribute to air pollution, but becoming a full member of WTO brings positive effect to Vietnamese environment.

econ.GN↗

arXiv2025

The impact of institutional quality on the relation between FDI and house prices in ASEAN emerging countries

This study investigates the relationship between house prices and capital inflows in ASEAN emerging economies, and the impact of institutional quality on that relation. Using a unique balanced panel data set of six emerging countries in ASEAN from 2009 to 2019, we employ various econometric techniques to examine the impact of foreign direct investment (FDI) on the house price index. Our findings indicate a long-run relationship and Granger causality from FDI to the house price index in these markets, and we also find evidence of co-movement between the stock price index and the house price index. Additionally, our results suggest that better institutions reduce the impact of FDI on host country housing markets in the context of ASEAN emerging economies. This is one of the first studies to shed light on the role of institutional quality in the effect of FDIs on housing prices in this region.

econ.GN↗

arXiv2025

Investigation of Cross-border Banking Activities

This paper investigates cross-border lending behavior from the Group of Seven (G7) during the 2001-2013 period. We employ gravity model to consider how bilateral factors, global factors, and other determinants of pull factors affect cross -border lending . The empirical results demonstrate that driving factors for cross-border lending have been changing since the 2008 Global Financial Crisis . Particularly , continent variable has more significant correlation with cross-border claims during the post-crisis period, while distance variable becomes less important during that time than it was in the pre-crisis period. Additionally , higher lending claims is more likely related to common language after the financial crisis. Moreover, the role of pull factors, except the size of borrowing economies, is not significant in explaining cross-border banking activities since GFC.

q-fin.GN↗

arXiv2024

Anomalous Induced Density of Supercritical Coulomb Impurities in Graphene Under Strong Magnetic Fields

The Coulomb impurity problem of graphene, in the absence of a magnetic field, displays discrete scale invariance. Applying a magnetic field introduces a new magnetic length scale $\ell$ and breaks discrete scale invariance. Moreover, a magnetic field is a singular perturbation as it turns complex energies into real energies. Nonetheless, the Coulomb potential must be regularized with a length $R$ at short distances for supercritical impurities. We investigate the structure of the induced density of a filled Landau impurity band in the supercritical regime. The coupling between Landau level states by the impurity potential is nontrivial and can lead to several anomalous effects. First, we find that the peak in the induced density can be located away from the center of the impurity, depending on the characteristics of the Landau impurity bands. Second, the impurity charge is screened, despite the Landau impurity band being filled. Third, anticrossing impurity states lead to additional impurity cyclotron resonances.

cond-mat.mes-hall↗

arXiv2023

Mutual information and correlations across topological phase transitions in topologically ordered graphene zigzag nanoribbons

Graphene zigzag nanoribbons, initially in a topologically ordered state, undergo a topological phase transition into crossover phases distinguished by quasi-topological order. We computed mutual information for both the topologically ordered phase and its crossover phases, revealing the following results: (i) In the topologically ordered phase, A-chirality carbon lines strongly entangle with B-chirality carbon lines on the opposite side of the zigzag ribbon. This entanglement persists but weakens in crossover phases. (ii) The upper zigzag edge entangles with non-edge lines of different chirality on the opposite side of the ribbon. (iii) Entanglement increases as more carbon lines are grouped together, regardless of the lines' chirality. No long-range entanglement was found in the symmetry-protected phase in the absence of disorder.

cond-mat.mes-hall↗