Universal entanglement losses induced by angular uncertainty

We study the diffraction of two maximally entangled qubits encoded into spatial modes of light with orbital angular momenta $\pm \hbar l_0$, on angular apertures. Exploiting the uncertainty relation between angular position and momentum, we quantify the diffraction-induced entanglement loss, for different $l_0$, as a function of the angular uncertainty $\Delta \phi$ induced by the apertures. We demonstrate that the degradation of entanglement follows a universal law parametrised by the product $l_0\Delta \phi$ alone.} {We study the diffraction of two photonic qubits, which are initially maximally entangled in their orbital angular momenta, on angular apertures. Using the uncertainty relation between angular position and momentum, we show that the diffraction-induced entanglement losses exhibit universal behaviour.