Abstract

Charge detection utilizing a biased quantum point contact (QPC) has become an essential probe for studying the electronic properties of nanoscale devices such as coupled few electron quantum dots. In order to reach a sufficient sensitivity to detect at least single electron charging events, the detector QPC is usually strongly biased at VQPC » 1meV and IQPC ~ 1 nA. As a result the QPC emits energy quanta that can be reabsorbed in the device components. This back–action ultimatively results in decoherence limiting possible applications for instance in the field of quantum information processing. In the presentation I will discuss recent experiments in which the non–equilibrium back–action of a biased QPC onto serially coupled double or triple quantum dots is explored. Back-action can be observed as a ratchet current through a double quantum dot or as telegraph noise in the detector current. In the case of two adjacent but electrically separate QPCs, a strong bias applied to one QPC results in a counterflow current flowing in the opposite direction through the second unbiased QPC . In all these experiments, energy quanta are emitted by a biased QPC and absorbed in a second unbiased nanostructure.