Chapter 6 - Microwave spectroscopy on quantum dots

Abstract

This chapter investigates millimeter wave spectroscopy on quantum point contacts and single and coupled quantum dots. In a detailed study of the response of quantum point contacts, the influence of potential asymmetries in such devices have been shown. Photon-assisted transport through single and double quantum dots in the high-frequency regime could clearly be demonstrated. This method can be applied for spectroscopy of quantum dots far from equilibrium, which is demonstrated by electron spin resonance in a single dot at high magnetic fields. Finally, a millimeter-wave interferometer is applied to perform coherent spectroscopy on coupled quantum dots. The newly developed interferometer covers the whole millimeter-wave regime and allows both magnitude- and phase-sensitive detection, In the measurements shown, the high-frequency conductance through the double quantum dot was detected. Photon-assisted tunneling through the quantum dots can be employed for spectroscopy on the few-electron system. Naturally coupling two quantum dots will result in the formation of an "artificial molecule." As a consequence of two strongly coupled dots, Rabi oscillations will occur. These can be probed directly in time-dependent measurements, where the electromagnetic field interacts with the oscillating valence electron.