  We demonstrate a possibility for exciton Bose-Einstein condensation in
individual small-diameter (~1-2 nm) semiconducting carbon nanotubes. The effect
occurs under the exciton-interband-plasmon coupling controlled by an external
electrostatic field applied perpendicular to the nanotube axis. It requires
fields ~1 V/nm and temperatures below 100 K that are experimentally accessible.
The effect offers a testing ground for fundamentals of condensed matter physics
in one dimension and opens up perspectives to develop tunable coherent
polarized light source with carbon nanotubes.
