Active drains and causality

Paul Kinsler

    Blackett Laboratory
    Imperial College London,
    Prince Consort Road,
    London SW7 2AZ
    United Kingdom.

    Phys. Rev. A82, 055804 (2010).
    doi:10.1103/PhysRevA.82.055804
    arXiv:1008.2088

    Dr.Paul.Kinsler@physics.org


The concept of an active drain has been used recently to
provide an optical element which manages to perfectly sink
incoming electromagnetic radiation.  Here I show that without
prior knowledge of the incoming signal, an element attempting
respond as an active localized drain cannot succeed.