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We study the formation of stable homonuclear and heteronuclear pentamers from ultracold atoms via a generalized stimulated Raman adiabatic passage scheme. The atom-molecule dark-state solutions for the system are obtained, and the linear instability and the adiabatic fidelity of the dark state are investigated. We also discuss the effects of external field parameters on the conversion efficiency.

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The quantum transition of three coupled Bose-Einstein condensates subjected to an artificial gauge potential is studied in a full quantum description. It shows that as the attractive atomic interaction increases, the system undergoes a transition from non-degenerate to degenerate ground states. This quantum transition point will reach the phase transition point predicted by the mean-field methods when the particle number is infinite, and it can be controlled via the 'magnetic flux' ϕ induced by the artificial gauge potential. Specially, when ϕ is odd times of π, around the zero-interaction point, i.e. the phase transition point predicted by the mean-field approach, an interesting quantum phenomenon occurs that the system with finite particles shows different parity effects at two sides of this point. For attractive (repulsive) interaction, the ground state is non-degenerate only when the particle number is a multiple of two (three). The parity effect is due to the symmetric properties of the system at different sides of the transition point. The transition point is then protected by the system symmetry and does not change with the particle numbers.

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