Effect of depolarizing noise on entangled photons

Entangled photons are important resources for quantum information. Especially, in quantum cryptography, the polarization entangled photons are highly secured. However, the entanglement of photon can hold in isolated system. In realistic system, the entangled photons inevitably interact with environment. In this work, we study the effect of depolarizing noise on the two general entangled qubits. The entangled photon are prepared with different entangled states and send to the depolarizing channel. We measure the entanglement quality by using concurrence. When the entangled photons interact to the depolarizing noise, the entanglement quality of photons will be degraded, and the concurrence of entangled photons reduces to 0. Moreover, we also apply Hadamard gate to the entangled qubits and send to the depolarizing channel. The Hadamard gate can filter the maximally entangled qubits in the depolarizing channel. (paper)