Quantum noise eater for a single photonic qubit

We propose a quantum noise eater for a single qubit and experimentally verify its performance for recovery of a superposition carried by a dual-rail photonic qubit. We consider a case when only one of the rails (e.g., one of interferometric arms) is vulnerable to noise. A coherent but randomly arriving photon penetrating into this single rail causes a change of its state, which results in an error in a subsequent quantum information processing. We theoretically prove and experimentally demonstrate a conditional full recovery of the superposition by this quantum noise eater.