Browsing by Author "Alavi A"

Now showing 1 - 2 of 2
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    Eliminating the wave-function singularity for ultracold atoms by a similarity transformation
    (American Physical Society, 2020-11-20) Jeszenszki P; Ebling U; Luo H; Alavi A; Brand J
    A hyperbolic singularity in the wave function of δ-wave interacting atoms is the root problem for any accurate numerical simulation. Here, we apply the transcorrelated method, whereby the wave-function singularity is explicitly described by a two-body Jastrow factor, and then folded into the Hamiltonian via a similarity transformation. The resulting nonsingular eigenfunctions are approximated by stochastic Fock-space diagonalization with energy errors scaling with 1/Μ in the number M of single-particle basis functions. The performance of the transcorrelated method is demonstrated on the example of strongly correlated fermions with unitary interactions. The current method provides the most accurate ground-state energies so far for three and four fermions in a rectangular box with periodic boundary conditions.
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    Signatures of the BCS-BEC crossover in the yrast spectra of Fermi quantum rings
    (American Physical Society, 2021-05) Ebling U; Alavi A; Brand J
    We study properties of the lowest energy states at nonzero total momentum (yrast states) of the Hubbard model for spin-½ fermions in the quantum ring configuration with attractive on-site interaction at low density. In the one-dimensional (1D) case we solve the Hubbard model using the Bethe ansatz, while for the crossover into the 2D regime we use the Full-Configuration-Interaction Quantum Monte Carlo method to obtain the yrast states for the spin-balanced Fermi system. We show how the yrast excitation spectrum changes from the 1D to the 2D regime and how pairing affects the yrast spectra. We also find signatures of fragmented condensation for certain yrast states usually associated with dark solitons.