Single-photon detection of THz-waves using quantum dots

We demonstrate two mechanisms of single photon detection in the THz spectral region by using gate-voltage-induced lateral GaAs/AlGaAs quantum dots (QDs). Firstly, a QD in strong magnetic fields (B = 3-4 T) is operated as a single electron transistor (SETs). THz-photons (1.8-1.5 THz) excite the QD via cyclotron resonance, and electrical polarization is thereby induced within the QD. The polarization, in turn, affects the SET conductance. Secondly, a SET with parallel double QDs is operated without magnetic fields, where GHz-photons (about 500 GHz) excite and ionize one of the QDs, which is, in turn, probed by the other QD to change the SET conductance.