Quantum Information, Computation and Complexity * Programme at the Institut Henri Poincare, January 4th – April 7th, 2006 * Organizers: Ph.Grangier, M.Santha and D.L.Shepelyansky * Lectures have been filmed by Peter Rapcan and Michal Sedlak from Bratislava with the support of the Marie Curie RTN CONQUEST A trimester at the Centre Emile Borel - Institut Henri Poincare is devoted to modern developments in a rapidly growing field of quantum information and communication, quantum computers and algorithms for complex problems. The Programme includes lecture courses, workshops, discussion sessions and seminar series.
Abstract We consider dilute Bose gases on the three-dimensional unit torus that interact through a pair potential with scattering length of order
Nκ−1 N κ - 1 , for some
κ>0 κ > 0 . For the range
κ∈[0,431) κ ∈ [ 0 , 1 43 ) , Adhikari et al. (Ann Henri Poincaré 22:1163–1233, 2021) proves complete BEC of low energy states into the zero momentum mode based on a unitary renormalization through operator exponentials that are quartic in creation and annihilation operators. In this paper, we give a new and self-contained proof of BEC of the ground state for
κ∈[0,201) κ ∈ [ 0 , 1 20 ) by combining some of the key ideas of Adhikari et al. (Ann Henri Poincaré 22:1163–1233, 2021) with the novel diagonalization approach introduced recently in Brooks (Diagonalizing Bose Gases in the Gross–Pitaevskii Regime and Beyond, arXiv:2310.11347 ), which is based on the Schur complement formula. In particular, our proof avoids the use of operator exponentials and is significantly simpler than Adhikari et al. (Ann Henri Poincaré 22:1163–1233, 2021).