arXiv subjects

Hong-Yi Chen

Publications and source records attributed to Hong-Yi Chen.

At least 19 recordsLinked to original sources

arXiv2026

Rashba Spin-Orbit Driven Topological Phase Transitions in Heterogeneous Armchair Honeycomb Nanoribbons

We investigate the emergence of nontrivial topological phases in heterogeneous armchair honeycomb nanoribbons arising from the interplay between structural geometry and Rashba spin-orbit coupling (RSOC). The system consists of a central RSOC-active region sandwiched between two pristine segments, forming interfaces between topologically distinct phases. As the RSOC strength increases, interface states emerge and become localized at the junctions, exhibiting robustness against edge perturbations. For finite ribbon widths, the RSOC induces a closing and subsequent reopening of the bulk energy gap, signaling a topological phase transition without altering the underlying lattice geometry. These findings reveal a route to engineering tunable topological states through the cooperative effects of interfacial structure and spin-orbit interactions.

cond-mat.mes-hall↗

arXiv2025

Continuous Wave Quantum Detection and Ranging with quantum heterodyne detection

In the continuous-wave Detection and Ranging technology, simultaneous and accurate range and velocity measurements of an unknown target are typically achieved using a frequency-modulated continuous wave (FMCW) with a heterodyne receiver. The high time-bandwidth product of the FMCW waveform facilitates the optimization and high-precision of these measurements while maintaining low transmission power. Despite recent efforts to develop the quantum counterpart of this technology, a quantum protocol for FMCW that enhances measurement precision in lossy channels with background noise has yet to be established. Here, we propose a quantum illumination protocol for FMCW technology that utilizes sum frequency generation and an entangled light source with low transmission power. This protocol demonstrates a 3 dB enhancement in the precision limit for high-loss channels compared to classical approaches, independent of the background noise level. This precision limit is achieved through quantum heterodyne detection (QHD), followed by signal processing. Moreover, in classical approaches, QHD is only optimal in high-loss channels when strong background noise is present. In weak background noise scenarios, our protocol can further provides precision enhancements up to 6 dB over classical methods with QHD.

quant-ph↗

arXiv2025

Impurity-Induced Interference at a Topological Boundary in an Infinite SSH Heterojunction

In this work, we investigate the coupling between a strong impurity and the topological boundary of an SSH heterojunction, composed of two SSH chains belonging to different topological classes. We show that impurity boundary coupling gives rise to bonding and antibonding states within the SSH bulk gap. This coupling produces an interference effect in the local density of states, as the impurity approaches the boundary the LDOS evolves from a single sharp peak to a characteristic double peak structure. Moreover, the interference strength can be quantified by the decay length of the bonding or antibonding wavefunction and by the energy splitting of the LDOS resonance peaks near the Fermi energy.

cond-mat.mes-hall↗

arXiv2023

Quantum LiDAR with Frequency Modulated Continuous Wave

The range and speed of a moving object can be ascertained using the sensing technique known as light detection and ranging (LiDAR). It has recently been suggested that quantum LiDAR, which uses entangled states of light, can enhance the capabilities of LiDAR. Entangled pulsed light is used in prior quantum LiDAR approaches to assess both range and velocity at the same time using the pulses' time of flight and Doppler shift. The entangled pulsed light generation and detection, which are crucial for pulsed quantum LiDAR, are often inefficient. Here, we study a quantum LiDAR that operates on a frequency-modulated continuous wave (FMCW), as opposed to pulses. We first outline the design of the quantum FMCW LiDAR using entangled frequency-modulated photons in a Mach-Zehnder interferometer, and we demonstrate how it can increase accuracy and resolution for range and velocity measurements by $\sqrt{n}$ and $n$, respectively, with $n$ entangled photons. We also demonstrate that quantum FMCW LiDAR may perform simultaneous measurements of the range and velocity without the need for quantum pulsed compression, which is necessary in pulsed quantum LiDAR. Since the generation of entangled photons is the only inefficient nonlinear optical process needed, the quantum FMCW LiDAR is better suited for practical implementations. Additionally, most measurements in the quantum FMCW LiDAR can be carried out electronically by down-converting optical signal to microwave region.

quant-ph↗

arXiv2017

Maps on positive definite operators preserving the quantum $χ_α^2$-divergence

We describe the structure of all bijective maps on the cone of positive definite operators acting on a finite and at least two-dimensional complex Hilbert space which preserve the quantum $χ_α^2$-divergence for some $α\in [0,1]$. We prove that any such transformation is necessarily implemented by either a unitary or an antiunitary operator. Similar results concerning maps on the cone of positive semidefinite operators as well as on the set of all density operators are also derived.

math-ph↗

arXiv2016

Effects of single- and multi-substituted Zn ions in doped-122 type iron-based superconductors

Recent experiments on Zn-substituted 122-type iron-based superconductors (FeSCs) at electron- and hole- doped region provide us with a testing ground for understanding the effect of Zn impurities in these systems. Our first-principle calculations of the electronic structure reveal that the Zn 3d orbitals are far below the Fermi level and chemically inactive, while the Zn 4s-orbital is partially occupied and its wave function overlapping with those 3d-orbitals of neighboring Fe-ions. This suggests that the impurity effect is originating in the Zn 4s-orbital, not its 3d-orbitals. Employing a phenomenological two-orbital lattice model for 122-FeSCs and the self-consistent Bogoliubov-de Gennes equations, we study how the Zn-impurities suppress the superconductivity in electron- and hole- doped compounds. Our obtained results qualitatively agree with the experimental measurements.

cond-mat.supr-con↗

arXiv2015

Synthesising Interprocedural Bit-Precise Termination Proofs (extended version)

Proving program termination is key to guaranteeing absence of undesirable behaviour, such as hanging programs and even security vulnerabilities such as denial-of-service attacks. To make termination checks scale to large systems, interprocedural termination analysis seems essential, which is a largely unexplored area of research in termination analysis, where most effort has focussed on difficult single-procedure problems. We present a modular termination analysis for C programs using template-based interprocedural summarisation. Our analysis combines a context-sensitive, over-approximating forward analysis with the inference of under-approximating preconditions for termination. Bit-precise termination arguments are synthesised over lexicographic linear ranking function templates. Our experimental results show that our tool 2LS outperforms state-of-the-art alternatives, and demonstrate the clear advantage of interprocedural reasoning over monolithic analysis in terms of efficiency, while retaining comparable precision.

cs.SE↗

arXiv2014

Simulating a two-dimensional frustrated spin system with fermionic resonating-valence-bond states

The frustrated Heisenberg $J_{1}-J_{2}$ model on a square lattice is numerically investigated by variational Monte Carlo simulations. We propose a antiferromagnetic fermion resonating-valence-bond (AF-fRVB) state that has ability to examine the entire phase diagram in the $J_{1}-J_{2}$ model. Two phase transition points, the second order around $J_{2}/J_{1}=0.45$ and the first order around $J_{2}/J_{1}=0.6$, can be extracted more clearly than the conventional bosonic RVB state. At the maximally frustrated point ($J_{2}/J_{1}=0.5$), the AF-fRVB state shows the variational ground-state energy in the thermodynamic limit very close to the one estimated by the projected entangled pair state at the largest bond dimension available. On the other hand, in the frustrated regime $0.4\lesssim J_{2}/J_{1}\leq0.5$, AF-fRVB states with $s_{+-}$ (using the terminology in the field of iron-based superconductors) and $d_{xy}$ pairing symmetries are degenerate in the thermodynamic limit, implying the existence of gapless Dirac excitations in the spinon spectrum.

cond-mat.str-el↗

arXiv2012

Effect of nonlocal interactions on the disorder-induced zero-bias anomaly in the Anderson-Hubbard model

To expand the framework available for interpreting experiments on disordered strongly correlated systems, and in particular to explore further the strong-coupling zero-bias anomaly found in the Anderson-Hubbard model, we ask how this anomaly responds to the addition of nonlocal electron-electron interactions. We use exact diagonalization to calculate the single-particle density of states of the extended Anderson-Hubbard model. We find that for weak nonlocal interactions the form of the zero-bias anomaly is qualitatively unchanged. The energy scale of the anomaly continues to be set by an effective hopping amplitude renormalized by the nonlocal interaction. At larger values of the nonlocal interaction strength, however, hopping ceases to be a relevant energy scale and higher energy features associated with charge correlations dominate the density of states.

cond-mat.str-el↗

arXiv2010

Analysis of the Disorder-Induced Zero Bias Anomaly in the Anderson-Hubbard Model

Using a combination of numerical and analytical calculations, we study the disorder-induced zero bias anomaly (ZBA) in the density of states of strongly-correlated systems modeled by the two dimensional Anderson-Hubbard model. We find that the ZBA comes from the response of the nonlocal inelastic self-energy to the disorder potential, a result which has implications for theoretical approaches that retain only the local self-energy. Using an approximate analytic form for the self-energy, we derive an expression for the density of states of the two-site Anderson-Hubbard model. Our formalism reproduces the essential features of the ZBA, namely that the width is proportional to the hopping amplitude $t$ and is independent of the interaction strength and disorder potential.

cond-mat.str-el↗

arXiv2010

Effect of Strong Correlations on the Disorder-Induced Zero Bias Anomaly in the Two-Site Anderson-Hubbard Model

Several recent exact diagonalization calculations have established that the Anderson-Hubbard model has a disorder-induced zero bias anomaly (ZBA) (also called a disorder-induced pseudogap) in the density of states. In order to understand the physics of the ZBA, we study a simplified problem---an ensemble of two-site molecules with random site energies---for which analytical results are possible. For this ensemble, we examine how the ZBA forms in both the weakly correlated (mean field) and strongly correlated limits. In the weakly correlated case, the ZBA can be understood as the result of level repulsion between bonding and antibonding molecular orbitals. A similar level repulsion occurs in the strongly correlated case too, but a larger contribution to the ZBA comes from the suppression of a triplet excitation mode. This inherently many-body mechanism does not have a counterpart in mean-field models.

cond-mat.str-el↗

arXiv2008

Electronic Correlations in Double Quantum Dots

We present a study of the electronic structure of two laterally coupled gaussian quantum dots filled with two particles. The exact diagonalization method has been used in order to inspect the spatial correlations and examine the particular spin singlet-triplet configurations for different coupling degrees between quantum dots. The outcome of our research shows this structure to have highly modifiable properties promoting it as an interesting quantum device, showing the possible use of this states as a quantum bit gate.

cond-mat.mes-hall↗

arXiv2006

The Fock-Darwin States of Dirac Electrons in Graphene-based Artificial Atoms

We have investigated the Fock-Darwin states of the massless chiral fermions confined in a graphitic parabolic quantum dot. In the light of the Klein tunneling, we have analyzed the condition for confinement of the Dirac fermions in a cylindrically-symmetric potential. New features of the energy levels of the Dirac electrons as compared to the conventional electronic systems are dicussed. We have also evaluated the dipole-allowed transitions in the energy levels of the dots. We propose that in the high magnetic field limit, the band parameters can be accurately determined from the dipole-allowed transitions.

cond-mat.mes-hall↗

arXiv2006

Spin-Orbit Coupling and Tunneling Current in a Parabolic Quantum Dot

We propose a novel approach to explore the properties of a quantum dot in the presence of the spin-orbit interaction and in a tilted magnetic field. The spin-orbit coupling within the quantum dot manifest itself as anti-crossing of the energy levels when the tilt angle is varied. The anti-crossing gap has a non-monotonic dependence on the magnitude of the magnetic field and exhibits a peak at some finite values of the magnetic field. From the dependence of the tunneling current through the quantum dot on the bias voltage and the tilt angle, the anti-crossing gap and most importantly the spin-orbit strength can be uniquely determined.

cond-mat.mes-hall↗

arXiv2006

Quantum interference in dirty d-wave superconductors

The local differential tunneling conductance on a Zn impurity in a disordered d-wave superconductors is studied. Quantum interference between many impurities leads to definitive quasiparticle spectra. We suggest that an elaborate analysis on impurity-induced spectra with quantum interference effect included may be able to pin down the sign and strength of the scattering potential of a Zn impurity in low density limit. Numerical simulations calculated with appropriately determined impurity parameters are in satisfactory agreement with the observations from scanning tunneling microscopy (STM) experiments even in subtle details.

cond-mat.supr-con↗

arXiv2004

The temperature dependence of the local tunnelling conductance in cuprate superconductors with competing AF order

Based on the $t-t'-U-V$ model with proper chosen parameters for describing the cuprate superconductors, it is found that near the optimal doping at low temperature ($T$), only the pure d-wave superconductivity ($d$SC) prevails and the antiferromagnetic (AF) order is completely suppressed. At higher $T$, the AF order with stripe modulation and the accompanying charge order may emerge, and they could exist above the $d$SC transition temperature. We calculate the local differential tunnelling conductance (LDTC) from the local density of states (LDOS) and show that their energy variations are rather different from each other as $T$ increases. Although the calculated modulation periodicity in the LDTC/LDOS and bias energy dependence of the Fourier amplitude of LDTC in the "pseudogap" region are in good agreement with the recent STM experiment [Vershinin $et al.$, Science {\bf 303}, 1995 (2004)], we point out that some of the energy dependent features in the LDTC do not represent the intrinsic characteristics of the sample.

cond-mat.supr-con↗

arXiv2004

LDOS modulations in cuprate superconductors with competing AF order: the temperature effect

Based upon a phenomenological $t-t'-U-V$ model and using Bogoliubov-de Gennes equations, we found that near the optimal doping $δ=0.15$ at low temperature ($T$), only the pure d-wave superconductivity (dSC) prevails and the antiferromagnetic (AF) order is completely suppressed. However, at higher $T$ the AF order with stripe modulation and the accompanying charge density wave (CDW) emerge, and they could exist even above the superconducting transition temperature. This implies that the existence of the CDW depends critically on the presence of the AF order, not so much on the dSC. The LDOS (local density of states) image indicates that the stripe modulation has an energy independent spacing of $5a/4a$ spreading over a $24a \times 48a$ lattice, corresponding to an average periodicity $4.8a$. This result may be relevant to the recent STM experiment [Vershinin $et al.$, Science {\bf 303}, 1995 (2004)].

cond-mat.supr-con↗

arXiv2004

Spatial Distribution of LDOS in Cuprate Superconductors With Magnetic-Field-Induced Stripe Modulation

A phenomenological model defined in a two dimensional lattice is employed to investigate the d-wave superconductivity and the competing antiferromagnetic order in cuprate superconductors. Near the optimally doped regime, we show that it is possible to induce the spin density wave (SDW) and the accompanying charge density wave (CDW) orders with stripe modulations by applying a magnetic field. The periods of the magnetic field induced SDW and CDW are $8a$ and $4a$, respectively. The spatial profiles of the local density of states (LDOS) at various bias energies have also been numerically studied. Near and beyond the energies of the vortex core states, we found that the LDOS may display the CDW stripe-like modulation throughout the whole magnetic unit cell. For energies closer to the zero bias, the stripes appear to be rather localized to the vortex. The intensity of the integrated spectrum of the LDOS shows that the strength of the stripe modulation is decaying away from the vortex core. This feature is in good agreement with STM experiments. The case for the magnetic-field induced SDW/CDW with 4-fold symmetry has also been studied.

cond-mat.supr-con↗