Excitation picture of an interacting Bose gas
arXiv:1407.4920 · doi:10.1016/j.aop.2014.08.022
Abstract
Atomic Bose-Einstein condensates (BECs) can be viewed as macroscopic objects where atoms form correlated atom clusters to all orders. Therefore, the presence of a BEC makes the direct use of the cluster-expansion approach --- lucrative e.g. in semiconductor quantum optics --- inefficient when solving the many-body kinetics of a strongly interacting Bose. An excitation picture is introduced with a nonunitary transformation that exclusively describes the system in terms of atom clusters within the normal component alone. The nontrivial properties of this transformation are systematically studied, which yields a cluster-expansion friendly formalism for a strongly interacting Bose gas. Its connections and corrections to the standard Hartree-Fock Bogoliubov approach are discussed and the role of the order parameter and the Bogoliubov excitations are identified. The resulting interaction effects are shown to visibly modify number fluctuations of the BEC. Even when the BEC has a nearly perfect second-order coherence, the BEC number fluctuations can still resolve interaction-generated non-Poissonian fluctuations.
58 pages, 6 figures
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- Bound-state signatures in quenched Bose-Einstein condensates
- Bose-Einstein condensation of Efimovian triples in the unitary Bose gas
- Hyperbolic Bloch equations: atom-cluster kinetics of an interacting Bose gas
- Evolution of the unitary Bose gas for broad to narrow Feshbach resonances
- Quantum kinetic theory of light-matter interactions in degenerate plasmas
- Resonance triplet dynamics in the quenched unitary Bose gas