This is a fundamental result; the conductance does not take on arbitrary values but is quantized in multiples of the conductance quantum G_0=2e^2/h, which is expressed through the electron charge e and the Planck constant h. The integer number N is determined by the width of the point contact and roughly equals the width divided by half the electron wavelength. As a function of the width of the point contact (or gate voltage in the case of GaAs/AlGaAs heterostructure devices), the conductance shows a staircase behavior as more and more modes (or channels) contribute to the electron transport. The step-height is given by G_Q.
