The parent comment is now deleted, so I don't know what was said. But as per your comment, a spin-1/2 particle in a magnetic field has only two available state

The parent comment is now deleted, so I don't know what was said. But as per your comment, a spin-1/2 particle in a magnetic field has only two available states when measuring the component of angular momentum in the direction of the field. Typically these would be referred to as Spin Up and Spin Down, with angular momentum 'eigenvalues' of +hbar/2 and -hbar/2. A qubit could be implemented by incorporating these two states. A spin-1/2 particle is one of the simplest systems for illustrating many of elementary properties of quantum mechanics, and there's still quite a lot of weirdness therein. Edit - there are only two states for measuring one component of angular momentum of a spin-1/2 particle regardless of whether that direction measured is aligned with the field or not. But only the direction aligned with the field is an 'eigenstate' of the system.