Photon counting detectors for the far infrared

Single-electron transistor (SET) operation of a quantum dot (QD), fabricated in a GaAs/AlxGa1-xAs heterostructure crystal is demonstrated to serve as an extremely high sensitivity detector of far-infrared (FIR). When the single QD is placed in a high magnetic field, the resonant conductance through the SET switches on (off) upon the excitation of just one electron to a higher Landau level inside the QD, thereby enabling us to detect individual events of FIR-photon absorption (lambda = 0.17 - 0.22 mm). Additionally, we demonstrate that the SET consisting of two parallel QDs operates as a high sensitivity detector of FIR approaching the single-photon counting level in the absence of magnetic fields.