Exact Results in Quantum Theory
Sala Duża Teoretyczna (229), ul. Hoża 69
2011-02-25 (14:15) 
Marcin Napiórkowski (KMMF UW)
On the minimization of Hamiltonians over pure Gaussian states
A Hamiltonian defi ned as a polynomial in creation and annihilation operators is considered. After a minimization of its expectation value over pure Gaussian states, the Hamiltonian is Wick-ordered in creation andannihillation operators adapted to the minimizing state. I will show that this procedure eliminates from the Hamiltonian terms of degree 1 and 2 that do not preserve the particle number, and leaves only the terms thatcan be interpreted as quasiparticles excitations.