Quantum gates by coupled quantum dots and measurement procedure in Si MOSFET

We investigated the quantum gates of coupled quantum dots, theoretically, when charging effects can be observed. We have shown that the charged states in the qubits can be observed by the channel current of the MOSFET structure.Comment: 3 pages, 2 figures, use revtex.sty. 'The Eleventh International Conference on Nonequilibrium Carrier Dynamics in Semiconductors (HCIS-11)',July 19-23, 199

Readout using Resonant Tunneling in Silicon Spin Qubits

Spin qubit systems are one of the promising candidates for quantum computing. The quantum dot (QD) arrays are intensively investigated by many researchers. Because the energy-difference between the up-spin and down-spin states is very small, the detection of the qubit state is of prime importance in this field. Moreover, many wires are required to control qubit systems. Therefore, the integration of qubits and wires is also an important issue. In this study, the measurement process of QD arrays is theoretically investigated using resonant tunneling, controlled by a conventional transistor. It is shown that the number of possible measurements during coherence time can exceed a hundred under the backaction of the measurements owing to the nonlinear characteristics of resonant tunneling. It is also discussed to read out the measurement results by the conventional transistor.Comment: 11 pages, 13 figure

Measurement of two-qubit states by quantum point contacts

We solve the master equations of two charged qubits measured by two serially coupled quantum point contacts (QPCs). We describe two-qubit dynamics by comparing entangled states with product states, and show that the QPC current can be used for reading out results of quantum calculations and providing evidences of two-qubit entanglement. We also calculate the concurrence of the two qubits as a function of dephasing rate that originates from the measurement. We conclude that coupled charge qubits can be effectively detected by a QPC-based detector.Comment: 10 pages, 8 figures. Full paper is prepare

Fano-Kondo effect through two-level system based on quantum dots

We theoretically study the Fano-Kondo effect in a triple quantum dot (QD) system where two QDs constitute a two-level system and the other QD works in a detector with electrodes. We found that the Fano dip is clearly modulated by strongly coupled QDs in a two-level system and a slow detector with no interacting QD. This setup suggests a new method of reading out qubit states.Comment: 5pages,6figure