The solution is two split the bar into one, two and four segments using two breaks. Let us call these three parts $A$, $B$ and $C$ respectively. $$ $$ Day 1: You give the worker $A$.
Day 2: He gives you $A$ and you give him $B$.
Day 3: You give him $A$.
Day 4: He gives you $A$ and $B$ and you give him $C$.
Day 5: You give him $A$.
Day 6: He gives you $A$ and you give him $B$.
Day 7: You give him $A$.