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PT symmetric scattering using passive acoustic with flow

We show both theoretically and experimentally that an acoustical wave in an airflow duct going through a pair of diaphragms, one with amplification and another with an equivalent amount of attenuation, displays all the features of a parity-time (PT) symmetric system. Using a scattering matrix formalism, we show the novel features which reflect the PT-symmetry of the scattering acoustical system. We show experimentally the existence of a transition between PT-symmetric scattering eigenstates, which are norm preserving, and symmetry-broken pairs of eigenstates exhibiting net amplification and loss.