  A recent development in studies of random non-Hermitian quantum systems is
reviewed. Delocalization was found to occur under a sufficiently large constant
imaginary vector potential even in one and two dimensions. The phenomenon has a
physical realization as flux-line depinning in type-II superconductors.
Relations between the delocalization transition and the complex energy spectrum
of the non-Hermitian systems are described. Analytical and numerical results
obtained for a non-Hermitian Anderson model are shown.
