A consultancy firm has three types of employees: part time interns, juniors and seniors. It is known that $20\%$ of the employees who are interns at the beginning of a period continue to be an intern, $10\%$ of them become junior and the others quit the job at t he beginning of the next period. $40\%$ of junior employees at the beginning of a period continue their career as junior, $10\%$ of them become senior and the others leave the company at the beginning of the next period. Half of the seniors at the beginning of a period continue their careers as seniors while the other half leave the company at the beginning of the next period. 

Define the states and construct one step probability transition matrix for the above process.