In the context of quantum tunneling of ultracold atoms in an optical trap, the atom does not escape completely out of the lattice, but rather shifts its position within the lattice. Quantum tunneling is a phenomenon where a particle can pass through a potential barrier that classically it would not have enough energy to overcome.
In the case of an optical lattice, the atoms are trapped by an arrangement of laser beams, creating a periodic potential. This potential forms a lattice-like structure where the atoms are localized at specific positions. However, due to the wave-like nature of quantum particles, there is a non-zero probability for an atom to tunnel through the potential barrier and occupy a neighboring lattice site.
The degree to which the atom tunnels depends on various factors such as the depth of the lattice potential, the temperature of the atoms, and the specific experimental conditions. In some cases, the tunneling may be relatively weak, causing the atom to predominantly remain in its initial lattice site. In other cases, the tunneling can be more significant, leading to the atom occupying multiple lattice sites or spreading out over a larger region within the lattice.
It's important to note that the exact behavior of ultracold atoms in an optical lattice depends on the specific experimental parameters and the quantum state of the atoms. Different systems can exhibit different tunneling characteristics, ranging from strong to weak tunneling effects.