If the phase angles α α x and α α y differ by exactly π π / 2 and the x amplitude equals the y amplitude the wave is circularly polarized. The Jones vector then becomes | ψ ψ ⟩ ⟩ = 1 2 ( 1 ± ± i ) exp ⁡ ⁡ ( i α α x ) where the plus sign indicates left circular polarization and the minus sign indicates right circular polarization. In the case of circular polarization, the electric field vector of constant magnitude rotates in the x–y plane.