arXiv subjects

Diptiman Sen

Publications and source records attributed to Diptiman Sen.

At least 19 recordsLinked to original sources

arXiv2026

Topological signatures in the quench dynamics of periodically driven quantum systems

We study the quench dynamics of graphene, without and with a staggered mass, following the sudden switch-on of circularly polarized light where coupling to a fermionic bath is also considered. Using an armchair nanoribbon, we compute the period-averaged bond current near the edge at successive stroboscopic times. For the isolated system, the current oscillates around a dc value which, we analytically show, equals the Floquet band currents weighted by their projected occupations; a nonzero dc current signals an induced topological phase. When coupled to a bath with a finite coupling, the current and conductance initially increase and then saturate, indicating a nonequilibrium steady state. In the limit of vanishingly small coupling, the period-averaged conductance becomes quantized after summing over bath chemical potentials shifted by integer multiples of the driving frequency, revealing the number of edge modes crossing the zero-quasienergy gap and the Floquet zone boundary gap. We support these results by computing the two-terminal conductance of a finite-size tight-binding model under a three-step driving protocol; the bond conductance after applying the sum rule corroborates our findings.

cond-mat.mes-hall↗

arXiv2026

Topological zero-reflection points in multi-terminal quantum wire junctions

We study scattering in noninteracting multi-terminal quantum wire junctions and show that junctions with dihedral symmetry can exhibit exact zero-reflection points for $N \ge 4$ terminals. By analyzing the scattering matrix, we identify these reflectionless points in the $(E,t')$ parameter space, where $E$ is the incident particle energy and $t'$ is the junction hopping amplitude. These points exhibit an even-odd dependence on $N$ and converge asymptotically to a common limiting value in the large-$N$ limit. We show that the reflectionless points are characterized by an integer winding number associated with the phase of the reflection amplitude, providing a topological description for their stability against weak on-site disorder. We also consider junctions with broken time-reversal symmetry and find that a magnetic flux can induce additional reflectionless points, including for the $N = 3$ case. For a four-terminal junction threaded by a $\pi$-flux, we identify a unique parameter regime in which the reflection amplitude vanishes over the entire energy band. Finally, we discuss experimental signatures through the behavior of Friedel oscillations and examine the stability of these reflectionless points in the presence of weak interactions.

cond-mat.mes-hall↗

arXiv2026

Second quantization of anyons and spin-anyon duality

Anyons exhibit a non-trivial interplay between local exclusion rules and non-local braiding and exchange phases, making a consistent commutation algebra and second-quantized formulation challenging. We develop an algebraic framework for Abelian anyons in one dimension with statistical phase $\theta$ = $\pi$/N that enforces a finite on-site occupancy of N-1 anyons with the exchange phase $\theta$ between different sites. Moreover, we introduce an exact Jordan-Wigner duality between $\pi$/3 anyons and spin-1 operators, allowing us to map a tight-binding anyon model to an XY-like spin-1 model. The model exhibits anyon-density-dependent flux, incompressible or gapless regions, and critical points with level crossings that appear as discontinuities in ground-state currents, momenta, fidelities, and correlation functions. Our second-quantization formalism establishes a novel spin anyon duality, offering a conceptually new route to realize anyons from spin Hamiltonians and to engineer corresponding device architectures.

cond-mat.str-el↗

arXiv2026

Emergent prethermal Bethe integrability in a periodically driven Rydberg chain

We study a chain of periodically driven Rydberg atoms and identify a class of drive protocols for which the system exhibits emergent prethermal Bethe integrability at special drive frequencies. We provide a perturbative analytic expression of its Floquet Hamiltonian in the large drive amplitude regime. We demonstrate integrability of the leading term of this Floquet Hamiltonian at special drive frequencies, which we identify, by mapping it to the Hamiltonian of the paradigmatic spin-$1/2$ ${\rm XXZ}$ chain. We support our analytical results by exact diagonalization studies on finite chains. Our numerical results on level statistics, half-chain entanglement entropy, and longitudinal magnetization of the driven chain brings out its emergent integrable nature at the special drive frequencies which persists up to a large prethermal timescale.

quant-ph↗

arXiv2026

Emergence of a molecular quantum liquid in one dimension

We investigate the fate of a one-dimensional lattice superfluid formed by hard-core bosons, aka `atoms' (alternatively, a free spinless Fermi sea) subjected to nearest-neighbor attractive Hubbard-like interactions only in subgroups of two sites. The system, as expected, stabilizes a fluid of dimerized molecules at large attractive interactions. However, the composite molecules have an effective meek hopping scale and dominant repulsive interactions solely due to virtual quantum fluctuations. Interestingly, at an intermediate attractive potential, the system realizes a phase-separated region where the system is in an absorbing state. We show that this phase-separated region is due to an emergent attractive interaction between the dimers which leads to a local charge-density wave puddle where particles effectively cluster with local half-filling. Moreover the molecular superfluid gets spontaneously charge-ordered in the addition of an unpaired atom, reflecting the extreme sensitivity of the system to the existence of lone atoms. Using density-matrix renormalization group studies and effective low-energy Hamiltonians, we isolate the quantum processes to uncover the physics behind molecule formation in a strongly interacting one-dimensional system.

cond-mat.quant-gas↗

arXiv2026

Floquet scars and prethermal fragmentation in a driven spin-one chain

We study the periodic dynamics of a spin-one chain driven using a square-pulse protocol with amplitude $Q_0$ and frequency $\omega_D$. The Hamiltonian of the spin chain hosts a thermodynamically large number of $Z_2$-valued conserved quantities $W_{\ell}$ on the links $\ell$. This allows us to study the Floquet dynamics of this chain within a given sector with fixed values of $W_{\ell}$. For the sector with all $W_{\ell}=1$, we find signatures of quantum many-body scar states for $\hbar \omega_D \gg Q_0$; they lead to oscillatory dynamics and fidelity revival for specific initial states. Upon lowering $\omega_D$, we find an ergodic regime exhibiting fast thermalization consistent with the prediction of the (Floquet) eigenstate thermalization hypothesis. In addition, we identify special drive frequencies $\omega_n^{\ast}= Q_0/(2n \hbar)$ (where $n = 1, 2, 3, \cdots$) at which the Floquet Hamiltonian exhibits prethermal strong Hilbert space fragmentation (HSF) with the largest fragment being ergodic; in contrast, a weak HSF is found at $\omega'_n= Q_0/[\hbar(2n+1)]$ (where $n = 0, 1, 2, \cdots$). We also study the sector with $W_{\ell} =\{\cdots 1,1,-1,1,1,-1 \cdots \}$ which shows strong HSF at $\omega_n^{\ast}$ but no fragmentation at $\omega'_n$. Our analysis indicates that the strong HSF in this sector harbors an integrable largest fragment. We provide numerical support for our analytical and perturbative results using exact-diagonalization (ED) studies on finite chains of length $L\le 24$. Our numerical results for entanglement entropy, fidelity, and correlation functions of the driven chain provide definitive signatures of prethermal strong HSF for both sectors.

cond-mat.stat-mech↗

arXiv2025

Anomalous topological phases in a Chern insulator connected to leads in a cylindrical geometry

The observed robustly quantized Hall conductance in quantum Hall systems and Chern insulators (CI) is normally understood in terms of the bulk topology of isolated systems, not coupled to leads. It is assumed that the leads act as inert reservoirs. Within a model of a CI coupled to leads with a cylindrical geometry, we show that this is not always true. We identify the Hall conductance with a boundary invariant, the winding number of the phase of the reflection coefficient. We find anomalous topological phases where the boundary invariant is not the same as the bulk Chern number, even in the limit of weak lead coupling.

cond-mat.mes-hall↗

arXiv2025

Su-Schrieffer-Heeger model driven by sequences of two unitaries: periodic, quasiperiodic, aperiodic, and random protocols

We study the effect of driving the Su-Schrieffer-Heeger model using two unitary operators $U_1$ and $U_2$ in different combinations; the unitaries differ in the values of the inter-cell hopping amplitudes. Specifically, we study the cases where the unitaries are applied periodically, quasiperiodically, aperiodically and randomly. For a periodic protocol, when $U_1 = e^{-i H_1 T/2}$ and $U_2 = e^{-i H_2 T/2}$ are applied alternately, we find that end modes may appear, but the number of end modes does not always agree with the winding number which is a $Z$-valued topological invariant. We then study the Loschmidt amplitude ($LA$) starting with a initial state which is an end mode of $H_1$. We find that the $LA$ exhibits pronounced oscillations whose Fourier transform has a peak at a frequency which is equal to the quasienergy of an end mode of $U$. Next, when $U_1$ and $U_2$ are applied in a quasiperiodic or aperiodic way (we consider the Fibonacci and Thue-Morse protocols as examples), we study the Loschmidt echo ($LE$) starting with an initial state which is an end mode of the Hamiltonian $H_1$. When the inter-cell hoppings differ by a small amount denoted by $\epsilon$, and the time period $T$ of each unitary is also small, the distance between the unitaries is found to be proportional to $\epsilon T$. We then find that the $LE$ oscillates around a particular value for a very long time before decaying to zero. The deviation of the value of the $LE$ from 1 scales as $\epsilon^2$ for a fixed value of $T$, while the time after which the $LE$ starts decaying to zero has an interesting dependence on $\epsilon$ and $T$. Finally, when $U_1$ and $U_2$ are applied in a random order, the $LE$ rapidly decays to zero with increasing time. We have presented a qualitative understanding of the above results.

cond-mat.mes-hall↗

arXiv2025

Refraction-induced transverse charge transport

We introduce a mechanism that produces a Hall-like transverse response in time-reversal-invariant materials, driven entirely by geometric effects. Specifically, we demonstrate that a tilted potential interface causes electron wave packets to undergo a refractionlike deflection upon transmission through the barrier, leading to a finite transverse current and a corresponding Hall-like conductance. Our analytical framework captures the essential features of this refraction-driven charge transport, and the resulting transverse conductance profile is corrob- orated by numerical simulations across different lattice models and device geometries. We further visualize our predicted effect through real-time wave packet dynamics, which reveals its purely geometric origin and the robustness of the transverse response. These findings establish a fundamentally distinct class of Hall-like transport phenomena in mesoscopic systems that preserve time-reversal symmetry.

cond-mat.mes-hall↗

arXiv2025

Metric response of relative entropy: A universal indicator of quantum criticality

The information-geometric origin of fidelity susceptibility and its utility as a universal probe of quantum criticality in many-body settings have been widely discussed. Here we explore the metric response of quantum relative entropy (QRE), by tracing out all but $n$ adjacent sites from the ground state of spin chains of finite length $N$, as a parameter of the corresponding Hamiltonian is varied. The diagonal component of this metric defines a susceptibility of the QRE that diverges at quantum critical points (QCPs) in the thermodynamic limit. We study two spin-$1/2$ models as examples, namely the integrable transverse field Ising model (TFIM) and a non-integrable Ising chain with three-spin interactions. We demonstrate distinct scaling behaviors for the peak of the QRE susceptibility as a function of $N$: namely a square logarithmic divergence in TFIM and a power-law divergence in the non-integrable chain. This susceptibility encodes uncertainty of entanglement Hamiltonian gradients and is also directly connected to other information measures such as Petz-R\'enyi entropies. We further show that this susceptibility diverges even at finite $N$ if the subsystem size, $n$, exceeds a certain value when the Hamiltonian is tuned to its classical limits due to the rank of the RDMs being finite; unlike the divergence associated with the QCPs which require $N \rightarrow \infty$.

cond-mat.stat-mech↗

arXiv2025

Floquet multiple exceptional points with higher-order skin effect

We investigate the rich non-equilibrium physics arising in periodically driven open quantum systems, specifically those realized within microcavity resonators, whose dynamics are governed by a non-Hermitian Hamiltonian hosting Floquet Exceptional Points (FEPs). By introducing a periodically quenched driving protocol, we analytically derive the Floquet effective Hamiltonian and determine the locations of multiple FEPs harbored within the Floquet bulk bands. We demonstrate that the pair-production and annihilation of these FEPs can be precisely controlled by fine-tuning the system parameters, and zero and $\pi$ FEPs are topologically characterized by robust integer quantized winding numbers. To probe these singularities, we introduce a bi-orthogonal Floquet fidelity susceptibility, whose value exhibits large non-zero peaks at the momentum points hosting FEPs in the Brillouin zone. Furthermore, the momentum-summed susceptibility displays a sharp divergence when the number of FEPs change with respect to the time period of the drive. Our findings also reveal the emergence of Floquet edge states around zero energy and Dirac-like dispersion around $\pi$. Moreover, our model reveals a higher-order skin effect, where the periodically driven Hamiltonian hosts skin modes localized at both edges and corners. These insights offer novel avenues for the Floquet engineering of topological singularities in driven dissipative systems, with significant potential for manipulating light and matter at the microscale.

cond-mat.mes-hall↗

arXiv2025

Phase and Photon Number Dependent NOON State Localization in Flat Band Lattices

Flat-band lattices supporting compact localized states provide a versatile platform for exploring unconventional transport phenomena in photonic, ultracold atomic, electronic, and other systems. Here, we investigate the transport of path-entangled multi-photon NOON states in a flat-band rhombic lattice and observe intriguing localization-delocalization features that depend on both the phase and photon number of the NOON states. To experimentally emulate photon number correlations, we develop an intensity correlation measurement protocol using coherent laser light with tunable relative phases. We first apply this protocol to show spatial bunching and anti-bunching of two-photon NOON states in a one-dimensional waveguide lattice. In the rhombic lattice, we show that for an even (odd) photon number $N$, localization occurs at $0 \, (\pi)$ phase of the NOON state with a probability of $2^{1-N}$, which is demonstrated up to eight photons. Our results open an exciting route towards understanding the dynamics of correlated photons in complex photonic networks.

physics.optics↗

arXiv2025

Heating suppression via two-rate random and quasiperiodic drive protocols

We study a random and quasiperiodically driven one-dimensional non-integrable PXP spin chain in a magnetic field for two distinct drive protocols. Each of these protocols involves square pulses with two driving frequencies which are integer multiples of each other. For the first class of protocols, the duration of the pulse is changed randomly by an amplitude $dT$ while for the second class we use a random/quasiperiodic dipolar drive, where the quasiperiodicity is implemented using the Thue-Morse (TM) or Fibonacci sequences. For both protocols, we identify parameter regimes for which the thermalization of the driven chain is drastically slowed down due to proximity to a two-rate drive induced exact dynamical freezing. We also study the properties of these driven system moving slightly away from the freezing limit. For the first type of protocols, we show the existence of special value of $dT$ for which the thermalization rate remains small and provide an analytic explanation for such slow thermalization. For the second class of protocols, in contrast to random/quasiperiodic drives involving a single frequency studied earlier, we find that the TM quasiperiodic drive leads to a distinctly slower thermalization than that for drive protocols which are either periodic or follow a random or quasiperiodic Fibonacci sequence. We provide a qualitative semi-analytic understanding of these phenomena either using an exact calculation for small system sizes or carrying out a perturbative analysis in the large drive-amplitude limit. Our analysis brings out the central role of such two-frequency protocols in the reduction of heating in driven quantum systems. We discuss experiments which can test our theory.

quant-ph↗

arXiv2025

Probing the Topological Anderson Transition in Quasiperiodic Photonic Lattices via Chiral Displacement and Wavelength Tuning

The interplay of topology and disorder in quantum dynamics has recently attracted significant attention across diverse platforms, including solid-state devices, ultracold atoms, and photonic systems. Here, we report on a topological Anderson transition caused by quasiperiodic modulation of the stronger intra-cell couplings in photonic Su-Schrieffer-Heeger lattices. As the quasiperiodic strength is varied, the system exhibits a reentrant transition from a trivial phase to a topological phase and back to a trivial phase, accompanied by the closing and reopening of the band gap around zero energy. Unlike the traditional detection of photonic topological edge modes, we measure the mean chiral displacement from the transport of light in the bulk of the lattices. In our photonic lattices with a fixed length, the propagation dynamics is retrieved by varying the wavelength of light, which tunes the inter-waveguide couplings.

physics.optics↗

arXiv2025

Topological phase transition through tunable nearest-neighbor interactions in a one-dimensional lattice

We investigate the phase diagram of a one-dimensional model of hardcore bosons or spinless fermions with tunable nearest-neighbor interactions. By introducing alternating repulsive and attractive interactions on consecutive bonds, we show that the system undergoes a transition from a bond-ordered (BO) phase to a charge-density wave-II (CDW-II) phase as the attractive interaction strength increases at a fixed repulsive interaction. For a specific interaction pattern, the BO phase exhibits topological properties, which vanish when the pattern is altered, leading to a transition from a topological BO phase to a trivial BO phase through a gap-closing point where both interactions vanish. We identify these phases using a combination of order parameters, topological invariants, edge-state analysis and Thouless charge pumping. By extending our analysis beyond half-filling, we explore the phase diagram across all densities and identify the superfluid (SF) and the pair-superfluid (PSF) phases, characterized by single-particle and bound-pair excitations at incommensurate densities. The proposed model is experimentally realizable in platforms such as Rydberg excited or ultracold atoms in optical lattices, offering a versatile framework to study such interplay between topology and interactions in low-dimensional systems.

cond-mat.quant-gas↗

arXiv2025

Quantum dynamics of a spin model with an extensive degeneracy

We study the role played by extensive degeneracy in shaping the nature of the quantum dynamics of a one-dimensional spin model for both ramp and periodic drive protocols. The model displays an extensive degenerate manifold of states for a specific value of one of the parameters of its Hamiltonian. We study a linear ramp which takes the spin model through this degenerate point and show that it leads to a deviation from the usual Kibble-Zurek behavior. We also study the St\"uckelberg oscillations in such a model for a ramp which passes twice through the degenerate point. Our study indicates that such oscillations are strongly suppressed leading to a distinct behavior compared to those arising from double passage through a quantum critical point. Finally, we study the periodic dynamics of the model and show, for a large drive amplitude, the existence of special drive frequencies at which the system exhibits an approximate emergent $U(1)$ symmetry. We study the effect of this emergent symmetry on the correlators of the driven system and demonstrate the existence of dynamic symmetry restoration at these frequencies. We study the fate of the emergent symmetry when the drive amplitude is decreased and discuss possible experiments to test our theory.

quant-ph↗

arXiv2024

Aspects of Hilbert space fragmentation in the quantum East model: fragmentation, subspace-restricted quantum scars, and effects of density-density interactions

We investigate a one-dimensional correlated-hopping model of spinless fermions with an East constraint. We first analytically unravel the complete fragmentation structure of this model by labeling each fragment by a unique root configuration and utilizing the transfer matrix method. We show that the growth of the size of each fragment of the model follows the widely studied Dyck sequence, and is therefore analytically tractable with the help of Catalan triangles. While the eigenstate thermalization hypothesis (ETH) does not hold within the full Hilbert space which exhibits Poisson statistics of the energy level spacing, an examination of various quantities restricted to the largest fragments shows that a weaker version of the subspace-restricted thermalization holds. This weaker violation of the ETH within the largest fragments is supported by the presence of subspace-restricted quantum many-body scars due to quantum fragmentation. Next, we show that the inclusion of a nearest-neighbor density-density interaction with strength $V$ induces a spectral transition within the largest fragment from a weakly ETH-violating phase containing scars to a statistical bubble localized phase as $V$ increases. In particular, the $V\to \infty$ limit produces an integrable model. We find that the addition of finite-$V$ stabilizes the ground state near half-filling while keeping intact the fragmentation structure of the East model. However, this behavior abruptly changes exactly at $V = \infty$ due to the emergence of a distinct fragmentation structure. The infinite-$V$ model has many interesting properties, among which the appearance of the ground state and the largest fragment at two different filling fractions is specially noteworthy. Finally, we propose an experimental setup to realize the infinite-$V$ model as a particular limit of a special kind of $t-V$ model with an on-site potential.

cond-mat.stat-mech↗

arXiv2024

Phases and phase transitions in a dimerized spin-$\mathbf{\frac{1}{2}}$ XXZ chain

We revisit the phase diagram of the dimerized XXZ spin-$\frac{1}{2}$ chain with nearest-neighbor couplings which was studied numerically in Phys. Rev. B 106, L201106 (2022). The model has isotropic $XY$ couplings which have a uniform value and $ZZ$ couplings which have a dimerized form, with strengths $J_a$ and $J_b$ on alternate bonds. We find a rich phase diagram in the region of positive $J_a, ~J_b$. We provide a detailed understanding of the different phases and associated quantum phase transitions using a combination of mean-field theory, low-energy effective Hamiltonians, renormalization group calculations employing the technique of bosonization, and numerical calculations using the density-matrix renormalization group (DMRG) method. The phase diagram consists of two Ising paramagnetic phases called IPM$_0$ and IPM$_\pi$, and a phase with Ising Neel order called IN; all these phases are gapped. The phases IPM$_0$ and IPM$_\pi$ are separated by a gapless phase transition line given by $0 \le J_a = J_b \le 1$ which is described by a conformal field theory with central charge $c=1$. There are two gapless phase transition lines separating IPM$_0$ from IN and IPM$_\pi$ from IN; these are described by conformal field theories with $c=\frac{1}{2}$ corresponding to quantum Ising transitions. The $c=1$ line bifurcates into the two $c=\frac{1}{2}$ lines at the point $J_a = J_b = 1$; the shape of the bifurcation is found analytically using RG calculations. A symmetry analysis shows that IPM$_0$ is a topologically trivial phase while IPM$_\pi$ is a time-reversal symmetry-protected topological phase (SPT) with spin-$\frac{1}{2}$ states at the two ends of an open system. The numerical results obtained by the DMRG method are in good agreement with the analytical results. Finally we propose experimental platforms for testing our results.

cond-mat.str-el↗