  We demonstrate a way to coherently control light at the nanoscale and achieve
coherent perfect absorption (CPA) by using epsilon-near-zero (ENZ) plasmonic
waveguides. The presented waveguides support an effective ENZ response at their
cut-off frequency, combined with strong and homogeneous field enhancement along
their nanochannels. The CPA conditions are perfectly satisfied at the ENZ
frequency, surprisingly by a subwavelength plasmonic structure, resulting in
strong CPA under the illumination of two counter-propagating plane waves with
appropriate amplitudes and phases. In addition , we investigate the nonlinear
response of the proposed ENZ plasmonic configuration as we increase the input
intensity of the incident waves. We demonstrate that the CPA phenomenon can
become both intensity- and phase-dependent in this case leading to new tunable
all-optical switching and absorption devices.
