arXiv subjects

Zahra Jalali-Mola

Publications and source records attributed to Zahra Jalali-Mola.

8 recordsLinked to original sources

arXiv2026

Collective light-matter interaction in plasmonic waveguide quantum electrodynamics

Rabi oscillations characterize light-matter hybridization in the waveguide quantum electrodynamics~(WQED) framework, with their associated decay rates reflecting excitation damping, yet their behavior remains unresolved when collective emitters are coupled to a collective waveguide mode. This scenario reveals a conceptually novel collective-light-collective-matter interaction, realizable when a timed-Dicke state~(TDS) of subwavelength emitters couples to a slow, delocalized surface-plasmon mode, forming a hybridized plasmon-polariton~(HPP). The HPP acquires its directionality from the TDS via momentum matching. It also exhibits plasmonic characteristics, with excitation frequencies following the surface-plasmon dispersion relation. We obtain a Rabi oscillation and a long-time decay that describe the HPP and use them to reveal weak- and strong-coupling regimes through the emergence of normal-mode splitting. By performing a finite-time Lyapunov-exponent analysis, we show that the HPP also exhibits instantaneous decay and identify three distinct decay regimes: early-time rapid, transient-time oscillatory, and long-time classical. Finally, by analyzing the emission spectrum, we observe an anticrossing of the peak doublets~(a feature also seen in cavity QED setups) which originates from quantum vacuum effects and the resulting non-Markovian HPP evolution in our WQED.

physics.optics↗

arXiv2025

Anomalous fluctuations of Bose-Einstein condensates in optical lattices

Fluctuations are fundamental in physics and important for understanding and characterizing phase transitions. In this spirit, the phase transition to the Bose-Einstein condensate (BEC) is of specific importance. Whereas fluctuations of the condensate particle number in atomic BECs have been studied in continuous systems, experimental and theoretical studies for lattice systems were so far missing. Here, we explore the condensate particle number fluctuations in an optical lattice BEC across the phase transition in a combined experimental and theoretical study. We present both experimental data using ultracold $^{87}$Rb atoms and numerical simulations based on a hybrid approach combining the Bogoliubov quasiparticle framework with a master equation analysis for modeling the system. We find strongly anomalous fluctuations, where the variance of the condensate number $δN_{\rm BEC}^2$ scales with the total atom number as $N^{1+γ}$ with an exponent around $γ_{\rm theo}=0.74$ and $γ_{\rm exp}=0.62$, which we attribute to the 2D/3D crossover geometry and the interactions. Our study highlights the importance of the trap geometry on the character of fluctuations and on fundamental quantum mechanical properties.

cond-mat.quant-gas↗

arXiv2025

Controlled Floquet Dynamics and Topological Bound States in Continuum via Colored Quantum Random Walks

We demonstrate the emergence and control of Floquet states and topological bound states in the continuum (TBICs) in a two-dimensional colored quantum random walk (cQRW) on a square lattice. By introducing three internal degrees of freedom-termed "colors"-and leveraging SU(3) group representations, we realize dispersive TBICs and intrinsic Floquet dynamics without the need for external periodic driving. Through Chern number calculations, we identify three distinct topological bands, revealing color-induced band mixing as a key mechanism underlying the natural formation of Floquet states. The cQRW framework enables precise tuning of quasi-energy spectra, supporting the emergence of localized edge states in topological band gaps and dispersive TBICs embedded within the bulk of other bands. These TBICs exhibit tunable group velocity, controllable excitation across energy regimes, and robustness, providing theoretical validation for their existence in a first-order Floquet system. Our findings position cQRWs as a powerful platform for investigating and harnessing TBICs and Floquet states, with potential applications in quantum information and communication technologies.

physics.optics↗

arXiv2023

Topological Bogoliubov quasiparticles from Bose-Einstein condensate in a flat band system

For bosons with flat energy dispersion, condensation can occur in different symmetry sectors. Here, we consider bosons in a Kagome lattice with $π$-flux hopping, which in the presence of mean-field interactions exhibit degenerate condensates in the $Γ$- and the $K$-point. We analyze the excitation above both condensates and find strikingly different properties: For the $K$-point condensate, the Bogoliubov-de Gennes (BdG) Hamiltonian has broken particle-hole symmetry (PHS) and exhibits a topologically trivial quasiparticle band structure. However, band flatness plays a key role in breaking the time reversal symmetry (TRS) of the BdG Hamiltonian for a $Γ$-point condensate. Consequently, its quasiparticle band structure exhibits non-trivial topology, characterized by non-zero Chern numbers and the presence of edge states. Although quantum fluctuations energetically favor the $K$-point condensate, the interesting properties of the $Γ$-point condensate become relevant for anisotropic hopping. The topological properties of the $Γ$-point condensate get even richer in the presence of extended Bose-Hubbard interactions. We find a topological phase transition into a topological condensate characterized by high Chern number and also comment on the realization and detection of such excitations.

cond-mat.quant-gas↗

arXiv2021

Synthetic plasmonic lattice formation through invariant frequency comb excitation in graphene structures

Nonlinear surface-plasmon polaritons~(NSPPs) in nanophotonic waveguides excite with dissimilar temporal properties due to input field modifications and material characteristics, but they possess similar nonlinear spectral evolution. In this work, we uncover the origin of this similarity and establish that the spectral dynamics is an inherent property of the system that depends on the synthetic dimension and is beyond waveguide geometrical dimensionality. To this aim, we design an ultra-low loss nonlinear plasmonic waveguide, to establish the invariance of the surface plasmonic frequency combs~(FCs) and phase singularities for plasmonic peregrine waves and Akhmediev breather. By finely tuning the nonlinear coefficient of the interaction interface, we uncover the conservation conditions through this plasmonic system and employ the mean-value evolution of the quantum NSPP field commensurate with the Schrödinger equation to evaluate spectral dynamics of the plasmonic FCs~(PFCs). Through providing suppressed interface losses and modified nonlinearity as dual requirements for conservative conditions, we propose exciting PFCs as equally spaced invariant quantities of this plasmonic scheme and prove that the spectral dynamics of the NSPPs within the interaction interface yields the formation of plasmonic analog of the synthetic photonic lattice, which we termed \textit{synthetic plasmonic lattice}~(SPL).

physics.optics↗

arXiv2019

Electrodynamics of tilted Dirac/Weyl materials: A unique platform for unusual surface plasmon polaritons

The electrodynamics of Weyl semimetals (WSMs) is an extension of Maxwell's theory where in addition to field strength tensor $F_{μν}$, an axion field enters the theory which is parameterized by a four-vector $b^μ=(b_0,\bf b)$. In the tilted Weyl matter (TWM) an additional set of parameters ${\bfζ}=(ζ_x,ζ_y,ζ_z)$ enter the theory that can be encoded into the metric of the spacetime felt by electrons in TWM. This allows an extension of Maxwell's electrodynamics that describes electric and magnetic fields in TWMs and tilted Dirac material (TDM) when $b^μ=0$. The tilt parameter $\bfζ$ appearing as off-diagonal metric entries mixing time and space components mingles $\bf E$ and $\bf B$ fields whereby modifies the inhomogeneous Maxwell's equations. Surface plasmon polariton (SPP) in these systems describes the propagation of electromagnetic waves at the {\it interface of two different spacetime geometries}. In the case of TDM, we find a characteristic dependence of SPP spectrum on the tilt parameter $ζ$ which can be used map $ζ$ from SPP measurements. In the case of TWM, depending on whether the interface with vacuum supports a Fermi arc or not, and whether the propagation direction is along the Fermi arc or transverse to it, we find many unusual spectral features for SPP modes. Our detailed study of the dependence of SPP spectra on the arrangements of three vectors $(\bf b, q,ζ)$, the first two of which are at our control, can be utilized to map the tilt characteristics and Fermi arc characteristics from SPP measurements.

cond-mat.str-el↗

arXiv2019

Polarization tensor for tilted Dirac fermion materials: Covariance in deformed Minkowski spacetime

The rich structure of solid state physics provides us with Dirac materials the effective theory of which enjoys the Lorentz symmetry. In non-symmorphic lattices, the Lorentz symmetry will be deformed in a way that the null energy-momentum vectors will correspond to on-shell condition for tilted Dirac cone dispersion. In this sense, tilted Dirac/Weyl materials can be viewed as solid state systems where the effective spacetime is non-Minkowski. In this work, we show that the polarization tensor for tilted Dirac cone systems acquires a covariant from only when the spacetime is considered to be an appropriate deformation of the Minkowski spacetime. As a unique consequence of the deformation of the geometry of the spacetime felt by the electrons in tilted Dirac cone materials, the Coulomb density-density interactions will generate corrections in both longitudinal and transverse channels. Therefore the transverse photons also participate in mediating the Coulomb forces, implying emergent Amperean forces associated with the tilt of the spacetime.

cond-mat.mes-hall↗

arXiv2018

Kinky plasmons in double layers of borophene-borophene and borophene-graphene

We investigate the collective plasmon modes in double layer of two dimensional materials where either one or both of the layers have tilted Dirac cone. Consistent with quite generic hydrodynamic treatment, similar to double layer graphene systems we find two branches of plasmons. The in-phase oscillations of the two layers disperses as $\sqrt q$, while the out-of-phase mode disperses as $q$. When even one of the layers hosts tilted Dirac cone spectrum, the plasmonic kink which is a salient feature of a monolayer of tilted Dirac cone is inherited by both of these branches. In double layers composed of graphene (nontilted) and borophene (tilted) where the two layers have two different Fermi velocities, the velocity scale of plasmonic modes is set by the greater of the two. The kink always takes place when each plasmon mode crosses an energy scale $ω_{\rm kink}$. When the two layers have different chemical potentials, there will be two such scales, and each of in-phase and out-of-phase modes develop two kinks. Moreover we find that an additional linearly dispersing overdamped mode of monolayer tilted Dirac cone system survives in the double layer system.

cond-mat.str-el↗