Fractional states in few-electron systems

We have observed fractional quantization of very few electrons confined in a semiconductor quantum dot using capacitance spectroscopy. The number of electrons per dot varies from 0 to about 40 as a function of bias on the quantum capacitors. The capacitance spectra have clear minima at gate voltages and magnetic fields, where the filling factors are 1/3 and 2/3. These measurements may allow direct comparison with few-particle calculations.