Physics – Condensed Matter – Quantum Gases
Scientific paper
2011-03-17
Phys. Rev. A 84, 013625 (2011)
Physics
Condensed Matter
Quantum Gases
7 pages, 7 figures
Scientific paper
10.1103/PhysRevA.84.013625
We investigate the energy spectrum of systems of two, three and four spin-1/2 fermions with short range attractive interactions both exactly, and within the scattering length approximation. The formation of molecular bound states and the ferromagnetic transition of the excited scattering state are examined systematically as a function of the 2-body scattering length. Identification of the upper branch (scattering states) is discussed and a general approach valid for systems with many particles is given. We show that an adiabatic ferromagnetic transition occurs, but at a critical transition point kF a much higher than predicted from previous calculations, almost all of which use the scattering length approximation. In the 4-particle system the discrepancy is a factor of 2. The exact critical interaction strength calculated in the 4-particle system is consistent with that reported by experiment. To make comparisons with the adiabatic transition, we study the quench dynamics of the pairing instability using the eigenstate wavefunctions.
Ceperley David. M.
Zhang Shiwei
Zhou Sheng-Qi
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