arXiv subjects

Jayendra N. Bandyopadhyay

Publications and source records attributed to Jayendra N. Bandyopadhyay.

At least 19 recordsLinked to original sources

arXiv2026

Construction-Dependent Floquet Topology in Circularly Driven $N$-Stacked Su-Schrieffer-Heeger Chains

We investigate construction-dependent Floquet topology in a two-dimensional lattice formed by stacking Su-Schrieffer-Heeger (SSH) chains with co-located sublattice orbitals. We present two constructions in the decoupled-chain limit. Construction-I: the constituent SSH chains are topologically trivial with winding number $w=0$. Construction-II: the constituent SSH chains are topologically nontrivial with $w=1$. Although these constructions are unitarily equivalent in the static limit, circular driving distinguishes them because the hopping processes related by the transformation correspond to different physical bond vectors and therefore acquire different Peierls phases. Using the Floquet-Sambe formalism, we determine the quasienergy spectra and phase diagrams in terms of the lower-band Chern number $C_L$ and directional Zak phases $(Z_x,\, Z_y)$. We find distinct Floquet phase structures, including low-frequency phases with $C_L = -3$ and $C_L = -4$ in the two constructions. Since the Chern number does not resolve the topology of the two quasienergy gaps separately, we further calculate the dynamical winding numbers $W_0$ and $W_π$, and verify the corresponding chiral edge states. In particular, at identical driving parameters, both constructions can have the same Chern numbers $C_L=-2$, while their gap-resolved winding numbers are $(W_0,\, W_π)=(0,\,+2)$ and $(-2,\,0)$, respectively. We also calculate the time-averaged optical Hall conductivity and show that $ C_Le^2/h$ determines its dc value for ideal full-band occupation. At the same time, its finite-frequency response contains photon-assisted contributions. Our results demonstrate that the physical construction of the constituent chains, although irrelevant to the static bulk spectrum, can play a decisive role in the Floquet topological structure. We discuss possible experimental realizations of the driven model.

cond-mat.mes-hall↗

arXiv2026

Quantum metrology with partially accessible chaotic sensors

Most quantum metrology protocols harness highly entangled probe states and globally accessible measurements to surpass the standard quantum limit. However, it is challenging to satisfy these requirements in realistic many-body sensors. We demonstrate that both of these constraints can be overcome in quantum chaotic sensors. Crucially, we establish that even in the presence of partial measurement accessibility, chaotic dynamics enables initial unentangled states to exhibit Heisenberg scaling of the quantum Fisher information, $I_α$ with time. In the weakly chaotic regime, we identify spin-coherent states placed at the edge of the regular islands in the mixed classical phase space as optimal initial states for enhanced sensitivity. On the other hand, in the strongly chaotic regime, $I_α$ is insensitive to the choice of the initial state. Notably, quantum-enhanced sensitivity is achieved even when a very low fraction ($\sim 5\%$) of the qubits are accessible. These results establish quantum chaos as a robust resource for quantum-enhanced sensing under realistic accessibility constraints on accessibility.

quant-ph↗

arXiv2025

Entanglement signatures of gapless topological phases in a $p$-wave superconductor

We explore the gapless topological phases of a $p$-wave superconductor, probing its rich topologically ordered phases and underlying quantum phenomena. The topological order of the system is characterized by studying its entanglement properties. This study confirms the bulk-boundary correspondence in the entanglement spectrum, even without a full bulk gap. For contractible bipartitions, the entanglement entropy varies non-monotonically with the chemical potential, displaying pronounced peaks at points where the bulk gap closes and reopens, signaling topological quantum phase transitions. This behavior remains robust in the thermodynamic limit. The entanglement entropy grows with system size for non-contractible bipartitions, indicating long-range entanglement in the gapless phase. These findings reveal the subtle interplay between symmetry, entanglement, and topology in gapless systems, and emphasize the role of entanglement-based diagnostics in identifying unconventional topological phases beyond the gapped paradigm.

cond-mat.other↗

arXiv2025

Study of entanglement and phase transitions in the coupled top systems with standard and nonstandard symmetries

We study classical and quantum versions of a coupled top system in the absence and the presence of nonlinear torsion in the individual top. The model without the torsion and couples two identical tops is well-known in the literature as the Feingold-Peres (FP) model. The permutation and chiral symmetries are preserved in the FP model. This model is classified under the BDI or chiral orthogonal symmetry class, one of the recently proposed nonstandard symmetry classes. For the nonzero torsional cases, we study two different models:(i) identical torsional term in the individual top (NZT-I model); (ii) non-identical torsional term due to their opposite sign in the individual top (NZT-II model). The NZT-I model has the permutation symmetry but no chiral symmetry; hence, this model is classified under the standard three-fold symmetry classes. On the other hand, the NZT-II model does not have permutation symmetry but has chiral symmetry; hence, this model is also classified as a nonstandard BDI symmetry class. In this study, we investigate the role of underlying symmetries on the entanglement between the two tops. Moreover, we explore the interrelations among classical phase space dynamics, energy transitions, and the entanglement between the tops.

quant-ph↗

arXiv2025

Harmonic emission as a probe to coherent transitions in the topological superconductors

We investigate the dynamical behavior of a topological superconducting system, demonstrating that its static configuration undergoes a transition driven by an intrinsic supercurrent. By analyzing the band population, we confirm the quasiparticle nature of the system both in the presence and absence of an external laser field. Under laser driving, we observe an enhancement in static emission forming a plateau-like structure, accompanied by multiple coherent transitions in the population. These transitions exhibit Rabi-like oscillations, attributed to the presence of Majorana bound states (MBS), further reinforcing the quasiparticle character of the model. Our results highlight the efficacy of laser driving as a probe of the system's topological and dynamical stability.

cond-mat.other↗

arXiv2025

Engineering harmonic emission through spatial modulation in a Kitaev chain

We investigate High-harmonic generation (HHG) in a dimerized Kitaev chain. The dimerization in the model is introduced through a site-dependent modulating potential, determined by a parameter $λ\in [-1:1]$. This parameter also determines the strength of the hopping amplitudes and tunes the system's topology. Depending upon the parameter $λ$, the HHG emission spectrum can be classified into three segments. The first segment exhibits two plateau structures, with the dominant one resulting from transitions to the chiral partner state, consistent with quasiparticle behavior in the topological superconducting phase. The second segment displays multiple plateaus, where intermediate states enable various transition pathways to higher conduction bands. Finally, the third segment presents broader plateaus, indicative of active interband transitions. In the $λ\leq0$ regime, we observe the mid-gap states (MGSs) hybridize with the bulk, suppressing the earlier observed harmonic enhancements. This highlights the key role of the intermediate states, particularly when MGSs are isolated. These results demonstrate that harmonic emission profiles can be selectively controlled through the modulating parameter $λ$, offering new prospects for tailoring HHG in topological systems.

cond-mat.other↗

arXiv2025

Adiabatic modulation of driving protocols in periodically driven quantum systems

We consider a periodically driven system where the high-frequency driving protocol consists of a sequence of potentials switched on and off at different instants within a period. We explore the possibility of introducing an adiabatic modulation of the driving protocol by considering a slow evolution of the instants when the sequence of potentials is switched on/off. We examine how this influences the long-term dynamics of periodically driven quantum systems. By assuming that the slow and fast timescales in the problem can be decoupled, we derive the stroboscopic (effective) Hamiltonian for a four-step driving sequence up to the first order in perturbation theory. We then apply this approach to a spin-$1/2$ system, where the adiabatic modulation of the driving protocol is chosen to produce an evolving emergent magnetic field that interacts with the spin. We study the emergence of diabolical points and diabolical loci in the parameter space of the effective Hamiltonian. Further, we study the topological properties of the maps of the adiabatic paths in the parameter space to the eigenspace of the effective Hamiltonian. In effect, we obtain a technique for tuning the topological properties of the eigenstates by selecting different adiabatic evolutions of the driving protocol, characterized by distinct paths in parameter space. This technique can be applied to any periodic driving protocol to achieve desirable topological effects.

quant-ph↗

arXiv2025

Investigating topological in-gap states in non-Hermitian quasicrystal with unconventional $p$-wave pairing

The interplay of onsite quasiperiodic potential, superconductivity, and non-Hermiticity is explored in a non-Hermitian unconventional superconducting quasicrystal described by Aubry-André-Harper (NHAAH) model with $p$-wave pairing. In previous studies, the non-Hermiticity was only considered at the onsite quasiperiodic potential of the NHAAH model, and Majorana zero modes (MZMs) were observed under open boundary conditions (OBC) in this model. In this work, we study an NHAAH model with $p$-wave pairing, where non-Hermiticity is considered onsite by introducing complex quasiperiodic potential and asymmetry at the hopping part. Our analysis uncovers triple-phase transitions, where topological, metal-insulator, and unconventional real-to-complex transitions coincide at weak $p$-wave pairing strength. Additionally, instead of the MZMs observed in the symmetric hopping case, we observe the emergence of in-gap states under OBC in this model. These in-gap states are robust against disorder, underscoring their topological protection. Therefore, unlike the MZMs, which are very challenging to experimentally realize, these in-gap states can be used in topological quantum computational protocols.

cond-mat.dis-nn↗

arXiv2024

Superconducting $p$-wave pairing effects on one-dimensional non-Hermitian quasicrystals with power law hopping

We study the effects of superconducting $p$-wave pairing on the non-Hermitian Aubry-André-Harper model with power-law hopping. For the case of short-range hopping, weak pairing leads to oscillating quasi-Majorana zero modes, turning to edge-localized Majorana zero modes as pairing strength increases. For the case of long-range hopping, we observe the emergence of massive Dirac modes having oscillatory behavior, similar to Majorana modes with weak pairing. The massive Dirac modes localize at the edges as the pairing strength grows. The superconducting pairing spoils the plateaus observed in the fractal dimension of all the energy eigenstates of the Aubry-André-Harper model with power-law hopping. The number of plateaus decreases with the increasing pairing strength for the weak non-Hermiticity in the system. The phase diagram of the system reveals that real and complex energy spectrums correlate differently with the localization properties of the eigenstates depending on the strength of pairing and hopping range.

cond-mat.supr-con↗

arXiv2024

Quasi-Majorana modes in the $p$-wave Kitaev chains on a square lattice

The topological characteristics of the $p$-wave Kitaev chains on a square lattice with nearest-neighbor and next-nearest-neighbor inter-chains hopping and pairing are investigated. Besides gapless exact zero-energy modes, this model exhibits topological gapless phase hosting edge modes, which do not reside strictly at zero energy. However, these modes can be distinguished from the bulk states. These states are known as pseudo- or quasi-Majorana Modes (qMMs). The exploration of this system's bulk spectrum and Berry curvature reveals singularities and flux-carrying vortices within its Brillouin zone. These vortices indicate the presence of four-fold Dirac points arising from two-fold degenerate bands. Examining the Hamiltonian under a cylindrical geometry uncovers the edge properties, demonstrating the existence of topological edge modes. These modes are a direct topological consequence of the Dirac semimetal characteristics of the system. The system is analyzed under open boundary conditions to distinguish the multiple MZMs and qMMs. This analysis includes a study of the normalized site-dependent local density of states, which pinpoints the presence of localized edge states. Additionally, numerical evidence confirms the robustness of the edge modes against disorder perturbations. The emergence of topological edge states and Dirac points with zero Chern number indicates that this model is a weak topological superconductor.

cond-mat.other↗

arXiv2024

Transport properties in a two-dimensional Su-Schrieffer-Heeger model in Quantum Hall Regime

We investigate the transport properties of a two-dimensional Su-Schrieffer-Heeger (2D SSH) model in the quantum Hall regime using non-equilibrium Green's function formalism (NEGF). The device Hamiltonian, where the 2D SSH model serves as the channel, is constructed using a nearest-neighbor tight-binding model. The effect of an external perpendicular magnetic field is incorporated into the contacts via Peierls substitution. We observe a transition from a gapped phase to a flat band regime at zero energy by varying the magnetic field. This transition is characterized by the emergence of highly localized states in the bulk or edges, which we observe by calculating local density-of-states (LDOS). We analyze transport in the system along two directions ($x$ and $y$) via transmission measurements, indicating a magnetic field-induced transition from insulating to metallic phase. The study of the energy spectrum of the system shows the formation of Landau levels. Moreover, the quantum number of the non-degenerate and degenerate Landau levels (transmission modes) can be any integer or only an odd integer, depending on diagonal, inter-cell, and intra-cell hopping strengths. From the analysis of the transport properties along $y$-direction, we find that edge modes play a crucial role in facilitating ballistic transport.

cond-mat.mes-hall↗

arXiv2024

Meijer-G Function with Continued Product and Integer Exponent: Performance of Multi-Aperture UOWC System over EGG Turbulence

Signal transmission over underwater optical wireless communication (UOWC) experiences the combined effect of oceanic turbulence and pointing errors statistically modeled using the sum of two Meijer-G functions. There is a research gap in the exact statistical analysis of multi-aperture UOWC systems that use selection combining diversity techniques to enhance performance compared to single-aperture systems. In this paper, we develop a general framework for the continued product and positive integer exponent for the sum of Meijer-G functions to analyze the exact statistical performance of the UOWC system in terms of multivariate Fox-H function for both independent and non-identically distributed (i.ni.d.) and independent and identically distributed (i.i.d.) channels. We also approximate the performance of a multi-aperture UOWC system with i.i.d. channels using the single-variate Fox-H function. Using the generalized approach, we present analytical expressions for average bit-error rate (BER) and ergodic capacity for the considered system operating over exponential generalized gamma (EGG) oceanic turbulence combined with zero-boresight pointing errors. We also develop asymptotic expressions for the average BER at a high signal-to-noise (SNR) to capture insights into the system's performance. Our simulation findings confirm the accuracy of our derived expressions and illustrate the impact of turbulence parameters for i.ni.d. and i.i.d. models for the average BER and ergodic capacity, which may provide a better estimate for the efficient deployment of UOWC.

eess.SP↗

arXiv2024

Probing topological phase transitions in Aubry-Andre-Harper model via high-harmonic generation

We study the high-harmonic generation in the Aubry-Andre-Harper (AAH) model. The modulating phase of the AAH model is used as a control parameter while preserving the chiral symmetry hosting the zero-energy edge states. The harmonic yield in a particular energy range exhibits a strong dependence on the control parameter with clear separation of the region of topologically trivial and nontrivial phases of the system. The threshold for the harmonic yield is found to serve as an all-optical tool for detecting topological phases. We extended our study with broken chiral symmetry by including the onsite potential. The introduction of the onsite potential lifts the degeneracy in the edge states, which affects the harmonic enhancement. Furthermore, it is also observed that the system's onsite strength can control the HHG yield.

cond-mat.str-el↗

arXiv2024

Non-Hermitian Aubry-André-Harper model with short- and long-range p-wave pairing

We investigate a non-Hermitian Aubry-André-Harper model with short-range, as well as long-range p-wave pairing. Here, the non-Hermiticity is introduced through the onsite potential. A comprehensive analysis of several critical aspects of this system is conducted, which includes eigenspectra, topological properties, localization properties, and the transition from real to complex energies. Specifically, we observe the emergence of Majorana zero modes in the case of short-range pairing, whereas massive Dirac modes emerge in the case of long-range pairing. More importantly, for the case of short-range pairing, we observe two simultaneous phase transitions or double phase transitions: topological and multifractal to localized phase. On the other hand, in the case of the long-range pairing, the topological and multifractal to localized transitions do not coincide. However, for both ranges of pairing, we identify a double phase transition where delocalized (or metallic) to a critical multifractal state is accompanied by an unconventional shift from real to complex energies. Unlike the short-range pairing case, we observe mobility edges in the long-range pairing case.

cond-mat.dis-nn↗

arXiv2024

Role of inter- and intraband current in laser interaction with bi-chromatic quasi-periodic crystals

We study the role of the inter- and intraband current in the laser interaction with the bi-chromatic quasi-periodic crystals. The interaction dynamics are simulated by solving the time-dependent Schrödinger equation in the $k$-space, and time evolution of the inter- and intraband current is obtained in a gauge invariant form. We observed that for certain bi-chromatic potential ratios, the energy band structure of the `valence band' and the `conduction band' facilitate the interband transitions only at the center or at the edge of the Brillouin zone, which leads to a very interesting population transfer mechanism between the bands. The temporal profile of the inter- and intraband current gives a detailed account of the interaction. The higher-order harmonic generation (HHG) is also studied for these bi-chromatic optical lattices, and the resultant harmonic yield is commented upon.

physics.atm-clus↗

arXiv2023

Laser induced Flqouet topological phases in a 2D weak topological insulator with unconventional nonlinear dispersion

Recently, we presented a two-dimensional (2D) model of a weak topological insulator formed by stacking an $N$ number of Su-Schrieffer-Heeger (SSH) chains \cite{Agrawal_2022-02}. We now study the influence of periodic driving on the topological properties of this system, which has all the fundamental symmetries, by shining it with circularly polarized light (CPL). The CPL is chosen because it breaks the time-reversal symmetry, which induces more exotic topological properties in the system. We investigate two different formations of the $N$ stacked SSH chains: all the SSH chains are topologically trivial in one formation and nontrivial in the other one. In contrast to the undriven or static case, both formations exhibit distinct topological behaviors. Here, we particularly derive the Floquet or the effective Hamiltonian using the replica method, which facilitates the study of high- and low-frequency regimes. We have discovered that this model exhibits laser-induced Floquet topological phases with higher Chern numbers. This system has nonlinear dispersion along both directions with additional $k_x-k_y$ coupling terms, which made the dispersion of this system {\it unconventional}. We closely study the role of this unconventional dispersion in the system at the low-energy limit and its response to periodic driving. The low-energy Hamiltonian also reveals a hierarchy in the gaps of the neighboring Floquet bands. Interestingly, though this model has nonlinear quasi-energy dispersion, it still shows some signatures of hierarchy, which was observed in the system with linear dispersion like graphene. Furthermore, we study the effect of linearly polarized light (LPL) on the topological properties of the system. In response to the LPL driving, the band-touching point either opens up or splits into two band-touching points.

cond-mat.mes-hall↗

arXiv2023

Cataloging topological phases of $N$-stacked Su-Schrieffer-Heeger chains by a systematic breaking of symmetries

Two-dimensional (2D) model of a weak topological insulator with $N$-stacked Su-Schrieffer-Heeger (SSH) chain is studied. This study starts with a basic model with all the fundamental symmetries (chiral, time-reversal, and particle-hole) preserved. Different topological phases are introduced in this model by systematically breaking the system's symmetries. The symmetries are broken by introducing different bonds (hopping terms) in the system. First, the chiral symmetry is broken by introducing hopping within each sub-lattice or intra-sub-lattice hopping, where the hopping strengths of the sub-lattices are equal in magnitudes but opposite in sign. Then, following Haldane, the time-reversal (TR) symmetry is broken by replacing the real intra-sub-lattice hopping strengths with imaginary numbers without changing the magnitudes. We find that breaking chiral and TR symmetries are essential for the weak topological insulator to be a Chern insulator. These models exhibit nontrivial topology with the Chern number $C = \pm 1$. The preservation of the particle-hole (PH) symmetry in the system facilitates an analytical calculation of $C$, which agrees with the numerically observed topological phase transition in the system. An interesting class of topologically nontrivial systems with $C=0$ is also observed, where the non-triviality is identified by quantized and fractional 2D Zak phase. Finally, the PH symmetry is broken in the system by introducing unequal amplitudes of intra-sub-lattice hopping strengths, while the equal intra-sub-lattice hopping strengths ensures the preservation of the inversion symmetry. We investigate the interplay of the PH and the inversion symmetries in the topological phase transition. A discussion on the possible experimental realizations of this model is also presented.

cond-mat.str-el↗

arXiv2023

Topological triple phase transition in non-Hermitian quasicrystals with complex asymmetric hopping

The triple phase transitions or simultaneous transitions of three different phases, namely topological, parity-time (PT) symmetry breaking, and metal-insulator transitions, are observed in an extension of PT symmetric non-Hermitian Aubry-André-Harper model. In this model, besides non-Hermitian complex quasi-periodic onsite potential, non-Hermiticity is also included in the nearest-neighbor hopping terms. Moreover, the nearest-neighbor hopping terms is also quasi-periodic. The presence of two non-Hermitian parameters, one from the onsite potential and another one from the hopping part, ensures PT symmetry transition in the system. In addition, tuning these two non-Hermitian parameters, we identify a parameters regime, where we observe the triple phase transition. Following some recent studies, an electrical circuit based experimental realization of this model is also discussed.

cond-mat.dis-nn↗