//the values from your start axis and rotation (x,y,z,rotation)
startQuaternion = new Quaternion(0, 1, 0, 1);
//the values from your end axis and rotation
endQuaternion = new Quaternion(0, 1, 0, 1);
 
/* the next section would go in an update event, like Event.ENTER_FRAME or TimerEvent.TIMER */
 
//if slerp is 0, the rotation will reflect the startQuaternion
//if slerp is 1, the rotation will reflect the endQuaternion
//any value between 0 and 1 will be a percentage of the rotation
//between the start and end. For example, .5 would be halfway between
//start and end.
slerp = 0; //transition this up to 1, something like slerp += .01;
 
//the main quaternion that you copy the rotation from
quaternion = Quaternion.slerp(startQuaternion, endQuaternion, slerp);
//Copies the rotation from the main quaternion into the cube's matrix
cube.transform.copy3x3(quaternion.matrix);