Bose-Einstein Condensation in Quasi-2D Trapped Gases

We discuss Bose-Einstein condensation (BEC) in quasi-2D trapped gases and find that well below the transition temperature $T_c$ the equilibrium state is a true condensate, whereas at intermediate temperatures $T<\mathrm{}{T}_c$ one has a quasicondensate (condensate with fluctuating phase). The mean-field interaction in a quasi-2D gas is sensitive to the frequency ${\omega }_0$ of the (tight) confinement in the “frozen” direction, and one can switch the sign of the interaction by changing ${\omega }_0$. Variation of ${\omega }_0$ can also reduce the rates of inelastic processes. This offers promising prospects for tunable BEC in trapped quasi-2D gases.