// Equal weight needs cos(theta/2) = sin(theta/2)  =>  theta/2 = pi/4  =>  theta = pi/2.
const theta = Math.PI / 2;
const c = circuit(2);
c.x(1);            // |01>: one excitation
c.cx(1, 0);
// controlled-RY(theta), control 0, target 1
c.ry(theta / 2, 1);
c.cx(0, 1);
c.ry(-theta / 2, 1);
c.cx(0, 1);
c.cx(1, 0);
return c;