We all know that the canonical commutation relation give you

$$[x^i,p_j]=i\hbar~\delta^i_j,\qquad i,j=1,2,3.$$

Is there a relativistic version such as

$$[x^a,p_b]=i\hbar~\delta_b^a,\qquad a,b=0,1,2,3~?$$

If so what is the time operator $x^0$?