For ultra-cold atoms, thermal depletion creates the BEC from the normal component, whereas quantum depletion ejects atoms from the BEC via interactions. Strong interactions in the Zero-Momentum State promote coherent quantum state transitions. As a result of quantum fluctuations, the particles will leave the ZMS (k=0) and occupy states above ZMS (k>0). This is quantum depletion. Quasi-particles with k>0 are described by the Hamiltonian using the pairs of creation and annihilation operators which correspond to the excitations of pairs of particles. Using Bogoliubov theory, it can be shown that it’s possible for particles to leave the ZMS in pairs and move to states with k>0. If ZMS exists at finite temperature, there will be thermal depletion.
Support the magazine and subscribe to the content
This is premium stuff. Subscribe to read the entire article.