OBSERVATION OF METASTABLE STATES IN SPINOR BOSE-EINSTEIN CONDENSATES

Bose-Einstein condensates have been prepared in long-lived metastable excited states. Two complementary types of metastable states were observed. The first is due to the immiscibility of multiple components in the condensate, and the second to local suppression of spin-relaxation collisions. Relaxation via recondensation of noncondensed atoms, spin relaxation, and quantum tunneling was observed. These experiments were done with F › 1 spinor Bose-Einstein condensates of sodium confined in an optical dipole trap. [S0031-9007(99)08657-3] PACS numbers: 03.75.Fi, 05.30.Jp, 64.60.My, 67.40.Fd Metastable states of matter, excited states which relax only slowly to the ground state, are commonly encountered. This slow relaxation often arises from the presence of free-energy barriers that prevent a system from directly evolving toward its ground state; if the thermal energy to overcome this barrier is not available, the metastable state may be long lived. Many properties of Bose-Einstein condensates in dilute atomic gases [1 ‐ 4] arise from metastability; indeed, such condensates are themselves metastable, since the true equilibrium state is a solid at these low temperatures. Bose-Einstein condensates in gases with attractive interactions [3] are metastable against collapse due to a kinetic energy barrier [5]. The persistence of rotations in condensates with repulsive interactions hinges on whether