Observation of Quantum Level Spectrum for Silicon Double Single-Electron Transistors

We observed the spectrum of quantum levels on series-connected double single-electron transistors (DSETs). The DSETs, composed of double quantum dots are formed with lateral confinements on the silicon-on-insulator substrate. To characterize DSETs, the electrical measurements were carried out at the base temperature of 22 mK by using a dilution refrigerator. The estimated energy spacing from the measurement characteristics agreed with the values from the geometrically defined quantum dots size. These results exhibit the significant potential of DSETs as a readout device for two charge quantum bits (qubits).