Quantized Charge Pumping through a Carbon Nanotube Double Quantum Dot
  We demonstrate single-electron pumping in a gate-defined carbon nanotube double quantum dot. By periodic modulation of the potentials of the two quantum dots we move the system around charge triple points and transport exactly one electron or hole per cycle. We investigate the pumping as a function of the modulation frequency and amplitude and observe good current quantization up to frequencies of 18 MHz where rectification effects cause the mechanism to break down. 
S. J. Chorley, J. Frake, C. G. Smith, G. A. C. Jones, and M. R.   Buitelaar
cond-mat.mes-hall