arXiv subjects

A. Levent Subaşı

Publications and source records attributed to A. Levent Subaşı.

5 recordsLinked to original sources

arXiv2026

Composite-Boson Ansatz for Fractional Quantum Hall Manifolds of Lattice Bosons at Generic Fillings $ν<1/2$

Hofstadter systems provide a lattice route to fractional quantum Hall physics, but their low-energy manifolds often lack simple wave-function descriptions. Here we present a composite-boson ansatz for a broad family of finite-size lattice-split Laughlin-quasihole manifolds in the low-flux Hofstadter--Bose--Hubbard model on a torus at generic fillings $ν<1/2$. Attaching two vortices to each boson yields reduced-flux orbitals from which we construct a many-body trial basis. Its translation-resolved rank reproduces the expected low-energy-manifold dimension and provides a composite-boson interpretation of the established quasihole counting previously inferred from generalized exclusion rules and thin-torus arguments. For smaller systems, diagonalization within the lowest-band-projected ansatz span closely reproduces the exact projected spectrum, while variational Monte Carlo extends the rank and energetic analysis to larger systems for which explicit subspace construction becomes costly. To probe the fractional quantum Hall character of these manifolds, we calculate their many-body Chern-numbers and show that localized added-flux excitations exhibit quasihole-like behavior, with fractional density depletion and an Aharonov--Bohm-free braiding phase that both track the effective filling. Together, these results establish a microscopic composite-boson framework for organizing a broad family of sub-half-filled fractional quantum Hall manifolds of lattice bosons.

cond-mat.quant-gas↗

arXiv2025

Neuromodulation via Krotov-Hopfield Improves Accuracy and Robustness of RBMs

In biological systems, neuromodulation tunes synaptic plasticity based on the internal state of the organism, complementing stimulus-driven Hebbian learning. The algorithm recently proposed by Krotov and Hopfield \cite{krotov_2019} can be utilized to mirror this process in artificial neural networks, where its built-in intra-layer competition and selective inhibition of synaptic updates offer a cost-effective remedy for the lack of lateral connections through a simplified attention mechanism. We demonstrate that KH-modulated RBMs outperform standard (shallow) RBMs in both reconstruction and classification tasks, offering a superior trade-off between generalization performance and model size, with the additional benefit of robustness to weight initialization as well as to overfitting during training.

cond-mat.dis-nn↗

arXiv2021

Phase separation in a mixture of trapped charged Bose-Einstein condensates

We study the phase separation configurations and their rotational properties for a mixture of two interacting charged Bose-Einstein condensates subject to a magnetic field trapped in disc and Corbino geometries. We calculate the ground state energies of azimuthal and radial phase separation configurations using the Gross-Pitaevskii and the Thomas-Fermi approximations. We show that the results for experimentally relevant system parameters from both approaches are in good agreement. The immiscible mixture in both geometries with equal intracomponent interactions favors the azimuthal phase separation for all intercomponent interactions. Only an imbalance in the intracomponent interactions can result in a transition to the radial phase separation, for which the transition becomes sensitive to the shape of the trap. We present phase diagrams as a function of the inter and intracomponent interactions. While the radial phase separation is widely favoured in disc geometry, the azimuthal phase separation is favoured for narrower Corbino geometries. We explore the rotational properties of the spatially separated condensates under the magnetic field, studying their angular momenta and velocity fields. The quantization of circulation breaks down for the azimuthal phase separation. In this case, the bulk region of the condensate continues to display superfluid flow behavior whereas the velocity field shows a rigid body behavior along the phase boundaries.

cond-mat.quant-gas↗

arXiv2020

Fulde-Ferrell states in unequally charged Fermi gases

Atoms with different internal states can exhibit different responses to an artificial magnetic field. An atomic gas mixture of two different components can therefore be interpreted as a mixture of two atomic gases carrying different synthetic charges. We consider the superfluid state of such unequally charged Fermi gases coupled to a magnetic field via the orbital effect and trapped in a torus geometry. The orbital coupling to the magnetic field favors an inhomogeneous superfluid state with optimum finite center-of-mass momentum pairing. The resulting population-balanced orbital Fulde-Ferrell (FF) state is robust against the magnetic field and does not undergo pair breaking unlike the conventional BCS and Fulde-Ferrell-Larkin-Ovchinnikov type pairing states under the Zeeman effect. We contrast the homogeneous and inhomogeneous cases emphasizing the advantages of the unequally charged systems and present their momentum distributions. We conclude that an unequally charged atomic Fermi gas system orbitally coupled to an artificial magnetic field provides an ideal candidate for experimental realization of the FF state.

cond-mat.quant-gas↗

arXiv2019

Mixture of two unequally charged superfluids in a magnetic field

The artificial magnetic fields engineered for ultra cold gases depend on the internal structure of the neutral atoms. Therefore the components of a mixture composed of two atomic gases can exhibit a different response to an artificial magnetic field. Such a mixture can be interpreted as a mixture of two atomic gases, carrying different synthetic charges. In this article, we consider such mixtures of two superfluids with unequal synthetic charges in a ring trap subject to a uniform artificial magnetic field. The charge imbalance in such a mixture changes the distribution of excited particles over angular momentum states compared to that of an equally charged mixture. This microscopic difference exhibits macroscopic consequences; such as the occurrence of an angular momentum transfer between two unequally charged components. Due to the inter-fluid atomic interactions in a ring, the angular momentum transfer can create a counter flowing persistent current in the weakly charged superfluid. Even in the limiting case of a charged and an uncharged superfluid mixture, a persistent current can be induced in the uncharged superfluid, despite the fact that it is not directly coupled to the magnetic field. The stability analysis shows that the induction depends on the interplay between inter-fluid interaction and the applied magnetic field. We obtain instability boundaries of the system and construct phase diagrams as a function of the inter-fluid interaction and the magnetic field. We investigate these properties employing the Bogoliubov approximation.

cond-mat.quant-gas↗