Ultracold bosons and entanglement in the tilted double-well

Ultracold bosons in a two-well potential are investigated via a four-mode model. It is shown that, for typical experimental parameters, the lowest lying entangled eigenstates cannot be described by the usual two-mode model that allows particles to occupy only the lowest level in each well. A small potential difference between the wells, or tilt, will cause the decoherence of entangled eigenstates. However, entangled states reappear when the tilt is equal to an integer multiple of twice the interaction strength