Gigahertz quantised charge pumping

The aim is to link the unit ampere to the elementary charge e, a true invariant of nature. The high level of control over single electrons needed to realise such a quantum current standard has led to much interest in devices employing Coulomb blockade of tunnelling[2]. The time taken for an electron to tunnel through the barriers defining the dot, limits the output current of such devices to several pA[3,4]. A substantial increase in the current would allow these devices to be of a real practical use as a standard. This thesis explores another pumping mechanism for single charges which does not rely on Coulomb blockade of tunnelling. Single electrons are transported through a periodically formed decoupled quantum dot (QD). The electrons transported can be regarded as particles “surfing” on the time dependent potential of the well generated by the three barriers, rather than tunnelling through the barriers as waves. Two phase-shifted sinusoidal signals applied directly to the metallic finger gates on an etched GaAs/AlGaAs quantum wire, pump the electrons at frequencies of up to f = 3.4 GHz, corresponding to a current level of 0.54 nA. This approach represents an alternative path not only in the realization of a high current high accuracy quantum standard for electrical current but also in single photon production and electron spin based quantum computing.