arXiv subjects

Raka Dasgupta

Publications and source records attributed to Raka Dasgupta.

13 recordsLinked to original sources

arXiv2026

Fluctuation Spectra and Response Function of Coupled Atomic and Molecular BECs

We investigate out-of-equilibrium properties of atomic molecular Bose Einstein condensates coupled through a Feshbach resonance, with the Feshbach coupling and detuning subject to Gaussian white noise. Using a bosonic Josephson junction framework and a Bloch sphere description, we examine the interplay of detuning, coherence, and noise governing the system dynamics. Coupling and detuning noise produce distinct fluctuation spectra, featuring both Feshbach resonant and symmetric off resonant peaks. We characterize the dispersive and absorptive response of the atom dimer system under periodic driving. The atom molecule hybridization at the Feshbach resonance maximizes the linewidth and minimizes both the effective temperature and the phase difference between the driving field and the system. This leads to an optimized power utilization and quality factor.

cond-mat.quant-gas↗

arXiv2026

Dynamical Crossover in Landau$-$Zener Tunneling in Dissipative Rydberg Lattices

In this work, we investigate the excitation dynamics of a Rabi-coupled dissipative Rydberg lattice with a time-dependent detuning. The system is analyzed using (i) a Lindblad master equation within a mean-field approximation and (ii) an effective non-Hermitian Hamiltonian framework. While the mean-field approach captures the emergence of an antiferromagnetic order in the Rydberg excitation profile, the non-Hermitian description provides direct insight into the complex energy spectrum and its avoided crossings, which govern the Landau$-$Zener dynamics. We identify a regime in which the sublattice population imbalance vanishes near the avoided crossing, resulting in identical Landau$-$Zener probabilities on the two sublattices. Beyond a critical effective blockade strength there is a dynamical crossover to another regime in which the sublattice population imbalance persists through the avoided crossing, giving rise to sublattice-dependent Landau$-$Zener probabilities. Furthermore, Rydberg interactions prolong the lifetime of Landau$-$Zener-induced excitations in the presence of weak dissipation and strong Rabi coupling. In contrast, for weak Rabi coupling, the Rydberg blockade inhibits excitation and suppresses the Landau$-$Zener transition probability.

cond-mat.quant-gas↗

arXiv2025

Roles of Polarization and Detuning in the Noise-induced Relaxation Dynamics of Atomic-Molecular Bose Condensates

We study the relaxation process of a resonant Bose gas under the influence of Gaussian white noise. We characterize the system dynamics in terms of the polarization or imbalance between the atoms and molecules, and the system coherence. The relaxation times corresponding to these two quantities are studied both using a mean-field model, and a Born Green Kirkwood Yvon hierarchy that takes into account the higher-order correlations. The role of the initial polarization and the Feshbach detuning are investigated. It is found with an increasing initial population imbalance, the longituidinal relaxation time (that governs the dyanamics of the polarization) grows, while the transverse relaxation time (that governs the dynamics of the coherence) decays. As for the varying Feshbach detuning, it is observed that the longituidinal relaxation time reaches its minima and its transverse counterpart reaches its maxima near the resonance. We also study how the initial polarization and the detuning affect physical quantities like drift speed, condensate fraction, fidelity and entanglement entropy etc, and find the results to be fully consistent with the behavior of the relaxation dynamics of the system.

cond-mat.quant-gas↗

arXiv2025

Different Phases in a Dissipative Rydberg Lattice : Roles of Occupancy and On-site Interaction

We study a two-level dissipative non-equilibrium bosonic Rydberg system in an optical lattice, where multiple atoms can occupy a single site. The system is treated using two different approaches: solution of the master equation using a mean-field approximation, and direct numerical simulation of an equivalent quantum model. It is found that, depending on the on-site interaction strength, the system can either be uniform or have an antiferromagnet-like density-wave structure in terms of the Rydberg excitation distribution. Our mean-field treatment detects an interesting oscillatory phase as well, but the numerical simulation in 1D does not capture it. The origin of all these phases are investigated by studying the spatial correlations, and by calculating the fixed points of the dynamics. It is observed that an initial population difference across the sublattices helps to enhance the density-wave order. The scaling behavior of the system is also analyzed and a signature of weak universality is obtained.

cond-mat.quant-gas↗

arXiv2025

Finite temperature phase diagram of the extended Bose-Hubbard model in the presence of disorder

We study the finite and non-zero temperature phase diagram of the Extended Bose-Hubbard Model for both pure and disordered systems. Such a system can be experimentally realized by trapping ultracold Rydberg atoms in optical lattices. By regulating the Rydberg excitation level and the lattice spacing, the system can be engineered to effectively have (i) only the nearest-neighbor interaction and (ii) both nearest-neighbor and next-nearest-neighbor interactions. For both of these situations, we construct the mean-field phase diagrams. It is found that the presence of a non-zero temperature significantly changes the phase diagram because now there is a competition between quantum and thermal fluctuations. We observe that conventional Mott insulator (MI) or charge-density-wave (CDW) lobes vanish at higher temperatures. In a pure system, they melt into a normal fluid (NF). In contrast, the insulating phases that survive at high temperatures in the presence of disorder are the Bose glass and the normal fluid. It is evident that the CDW lobes melt at a lower temperature and the Mott lobes melt at higher temperatures. These transition temperatures depend on the on-site and nearest-neighbor interaction strengths, respectively. It is also found that, with the addition of disorder, the insulating lobes are destroyed at a relatively lower temperature. The mathematical framework that we present here is capable of treating long-range interactions, disorder, and finite temperature simultaneously, and versatile enough so that it can be extended to study different forms of disorder or longer-range interactions.

cond-mat.quant-gas↗

arXiv2024

Periodic dynamics of population-imbalanced fermionic condensates in optical lattices

We investigate the dynamics of a population-imbalanced two-species fermionic system trapped in an optical lattice. The paired fermions here can form bosonic molecules via Feshbach coupling in the presence of an external magnetic field. It is shown that the natural fluctuations of the condensate fraction are periodic beyond a threshold Feshbach detuning; and below this threshold value, the condensate fraction shows no oscillation at all. The oscillation frequency vs. detuning curve is linear in nature. The slope and intercept of this line are shown to carry important information about the amount of imbalance present in the system, and the momentum space structure of the exotic phases.

cond-mat.quant-gas↗

arXiv2020

Exotic Pairing Structures in Population-Imbalanced Fermionic Systems: Dynamics as a Probe

We investigate a population-imbalanced two-species fermionic system where the resonantly-paired fermions combine to form bosonic molecules via Feshbach interaction. We study the dynamics of the intrinsic quantum fluctuations of the system. It is shown that the natural fluctuations of the condensate fraction consists of a fixed number of periodic components : indicating that these oscillations do not die out, and are sustained in the mean field dynamics of the system. These frequency components bear distinct signatures of the nature of pairing present in the system. We describe how a time dependent external magnetic field can be used to locate these oscillation frequencies, and thus to explore the momentum space structure of the population imbalanced system. We propose that this method can be used as an indirect experimental probe for detecting exotic phases like the breached pair state, FFLO state, and a phase-separated state comprising of BCS and normal regions.

cond-mat.quant-gas↗

arXiv2020

Cold Atom Quantum Simulator for String and Hadron Dynamics in Non-Abelian Lattice Gauge Theory

We propose an analog quantum simulator for simulating real time dynamics of $(1+1)$-d non-Abelian gauge theory well within the existing capacity of ultracold atom experiments. The scheme calls for the realization of a two-state ultracold fermionic system in a 1-dimensional bipartite lattice, and the observation of subsequent tunneling dynamics. Being based on novel loop string hadron formalism of SU(2) lattice gauge theory, this simulation technique is completely SU(2) invariant and simulates accurate dynamics of physical phenomena such as string breaking and/or pair production. The scheme is scalable, and particularly effective in simulating the theory in weak coupling regime, and also bulk limit of the theory in strong coupling regime up to certain approximations. This paper also presents a numerical benchmark comparison of exact spectrum and real time dynamics of lattice gauge theory to that of the atomic Hamiltonian with experimentally realizable range of parameters.

hep-lat↗

arXiv2016

Attraction-induced dynamical stability of a Bose-Einstein condensate in a nonlinear lattice

We study multiple-period Bloch states of a Bose-Einstein condensate with spatially periodic interactomic interaction. Solving the Gross-Pitaevskii equation for the continuum model, and also using a simplified discrete version of it, we investigate the energy-band structures and the corresponding stability properties. We observe a new "attraction-induced dynamical stability" mechanism caused by the localization of the density distribution in the attractive domains of the system and the isolation of these higher-density regions. This makes the superfluid stable near the zone boundary, and also enhances the stability of higher-periodic states if the nonlinear interaction strength is sufficiently high.

cond-mat.quant-gas↗

arXiv2016

Nonlinear Phenomena of Ultracold Atomic Gases in Optical Lattices: Emergence of Novel Features in Extended States

The system of a cold atomic gas in an optical lattice is governed by two factors: nonlinearity originating from the interparticle interaction, and the periodicity of the system set by the lattice. The high level of controllability associated with such an arrangement allows for the study of the competition and interplay between these two, and gives rise to a whole range of interesting and rich nonlinear effects. This review covers the basic idea and overview of such nonlinear phenomena, especially those corresponding to extended states. This includes "swallowtail" loop structures of the energy band, Bloch states with multiple periodicity, and those in "nonlinear lattices", i.e., systems with the nonlinear interaction term itself being a periodic function in space.

cond-mat.quant-gas↗

arXiv2013

Periodic dynamics of fermionic superfluids in the BCS regime

We study the zero temperature non-equilibrium dynamics of a fermionic superfluid in the BCS limit and in the presence of a drive leading to a time dependent chemical potential $μ(t)$. We choose a periodic driving protocol characterized by a frequency $ω$ and compute the fermion density, the wavefunction overlap, and the residual energy of the system at the end of $N$ periods of the drive. We demonstrate that the BCS self-consistency condition is crucial in shaping the long-time behaviour of the fermions subjected to the drive and provide an analytical understanding of the behaviour of the fermion density $n_{{\mathbf k}_F}$ (where ${\mathbf k}_F$ is the Fermi momentum vector) after a drive period and for large $ω$. We also show that the momentum distribution of the excitations generated due to such a drive bears the signature of the pairing symmetry and can be used, for example, to distinguish between s- and d-wave superfluids. We propose experiments to test our theory.

cond-mat.quant-gas↗

arXiv2011

Effects of three-body scattering processes on BCS-BEC crossover

We investigate the BCS-BEC crossover taking into account an additional three-body interaction, which is essentially the scattering between the Cooper pairs and the newly formed bosons. We show that if the two-body interaction is attractive, the presence of this additional three-body term makes the crossover process a nonreversible one. Starting from a stable Bose-Einstein condensate (BEC) state, crossover to BCS can be achieved; but if the BCS state is the starting point, instead of a stable BEC region, what the system crosses over to is a metastable condensed state.

cond-mat.quant-gas↗

arXiv2009

Stability of the Breached Pair State for a Two-species Fermionic System in the Presence of Feshbach Resonance

We investigate the phenomenon of fermionic pairing with mismatched Fermi surfaces in a two-species system in the presence of Feshbach resonance, where the resonantly-paired fermions combine to form bosonic molecules. We observe that the Feshbach parameters control the critical temperature of the gapped BCS superfluid state, and also determine the range over which a gapless breached pair state may exist. Demanding the positivity of the superfluid density, it is shown that although a breached pair state with two Fermi surfaces is always unstable, its single Fermi-surface counterpart can be stable if the chemical potentials of the two pairing species have opposite signs. This condition is satisfied only over a narrow region in the BEC side, characterized by an upper and a lower limit for the magnetic field. We estimate these limits for a mixture of two hyperfine states of $^6$Li using recent experimental data.

cond-mat.quant-gas↗