The electric field in a region surrounding the origin is uniform and along the $x$-axis. A small circle is drawn with the centre at the origin cutting the axes at points $A,B,C,D$ having co-ordinates $\left( {a,0} \right),\left( {0,a} \right),\left( { - a,0} \right),\left( {0, - a} \right);$ respectively as shown in figure then potential in minimum at the point