The incompressibility of the 2DEG at ν = p/q implies that a nonzero minimal energy is required to add charge to the system. An important consequence of Laughlin’s theory is that charge can be added only in the form of quasiparticle excitations of fractional charge e∗ = e/q. The discontinuity _μ in the chemical potential equals the energy that it costs to create p pairs of oppositely charged quasiparticles (widely separated from each other), _μ =p × 2_ with _ the quasiparticle creation energy.