  We report the realization of nanotube-based quantum dot structures that use
local electrostatic gating to produce individually controllable dots in series
along a nanotube. Electrostatic top-gates produce depletion regions in the
underlying tube; a pair of such depletion regions defines a quantum dot.
Transparencies of tunnel barriers as well as the electrostatic energies, within
single and multiple dots, can be tuned by gate voltages. The approach allows
accurate control over multiple devices on a single tube, and serves as a design
paradigm for nanotube-based electronics and quantum systems.
