• Corpus ID: 235352570

Many-body excitations in trapped Bose gas: A non-Hermitian view

@inproceedings{Grillakis2021ManybodyEI,
  title={Many-body excitations in trapped Bose gas: A non-Hermitian view},
  author={Manoussos G. Grillakis and Dionisios Margetis and Stephen Sorokanich},
  year={2021}
}

• M. Grillakis, D. Margetis, S. Sorokanich
• Published 3 June 2021
• Physics

We provide the analysis of a physically motivated model for a trapped dilute Bose gas with repulsive pairwise atomic interactions at zero temperature. Our goal is to describe aspects of the excited many-body quantum states by accounting for the scattering of atoms in pairs from the macroscopic state (condensate). We formally construct a many-body Hamiltonian, Happ, that is quadratic in the Boson field operators for noncondensate atoms. This Happ conserves the total number of atoms. Inspired by Wu (J. Math. Phys., 2:105–123, 1961), we apply a non-unitary transformation to Happ. Key in this non-Hermitian view is the pair-excitation kernel, which in operator form obeys a Riccati equation. In the stationary case, we develop an existence theory for solutions to this operator equation by a variational approach. We connect this theory to the one-particle excitation wave functions heuristically derived by Fetter (Ann. Phys., 70:67–101, 1972). These functions solve an eigenvalue problem for a J-self-adjoint operator. From the non-Hermitian Hamiltonian, we derive a one-particle nonlocal equation for low-lying excitations, describe its solutions, and recover Fetter’s excitation spectrum. Our approach leads to a description of the excited eigenstates of the reduced Hamiltonian in the N-particle sector of Fock space.