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Q: Fachverband Quantenoptik und Photonik

Q 56: Quantum Gases: Fermions II

Q 56.1: Vortrag

Donnerstag, 9. März 2023, 14:30–14:45, F342

Hartree-Fock-Bogoliubov Variational Approach for BCS Superfluidity — •Nikolai Kaschewski and Axel Pelster — Physics Department and Research Center OPTIMAS, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Germany

The established theory for the BCS-BEC crossover is based on formulating the underlying many-body problem with the functional integral and on performing a Hubbard-Stratonovich transformation in the Bogoliubov channel [1,2]. A saddle-point approximation reveals then that the whole BCS-BEC crossover can only be described once Gaussian fluctuations around the saddle point are taken into account, which turns out to be numerically quite demanding.

Here we tackle this many-body problem from another point of view. To this end we work out a variational approach for the underlying Hamilton operator in canonical field quantization, which includes not only the Bogoliubov but also the Hartree and the Fock channel. We determine the first beyond mean-field corrections and compare their results for the density profiles in the BCS regime with the corresponding ones of the functional integral theory.

[1] C. A. Sá de Melo, M. Randeria, and J. R. Engelbrecht, Phys. Rev. Lett. 71, 3202 (1993).

[2] J. R. Engelbrecht, M. Randeria, and C. A. R. Sá de Melo, Phys. Rev. B 55, 15153 (1997).