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Japanese Journal of Applied Physics

Quantum Gates Based on Electron Spins of Triple Quantum Dot

Hirotaka Sasakura, S. Adachi, Shunichi Muto

Published Oct 9, 2003• 3 citations
Publisher

Abstract

Quantum computation using electron spins in three-coupled dots of different sizes is proposed. By using photon-assisted tunnelling, Coulomb blockade and spin rotation of electrons, logic gates are realized by static and rotational magnetic fields and resonant optical pulses. The two-bit CNOT is numerically demonstrated by the time evolution of the density matrix. In addition, the Hamiltonian is described using pseudo-spin representation and the phase change during the gate operation is discussed.

DOI
10.1143/jjap.42.6308

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We propose a set of universal gate operations for the singlet-triplet qubit realized by two-electron spins in a double quantum dot, in the presence of a fixed inhomogeneous magnetic field. All gate operations are achieved by switching the potential offset between the two dots with an electrical bias, and do not require time-dependent control of the tunnel coupling between the dots. We analyze the two-electron dynamics and calculate the effective qubit rotation angle as a function of the applied electric bias. We present explicit gate sequences for single-qubit rotations about two orthogonal axes, and a CNOT gate sequence, completing the universal gate set.
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Using electrostatic gates to control the electron positions, we present a new controlled-NOT gate based on quantum dots. The qubit states are chosen to be the spin states of an excess conductor electron in the quantum dot; and the main ingredients of our scheme are the superpositions of space-time paths of electrons and the effect of Coulomb blockade. All operations are performed only on individual quantum dots and are based on fundamental interactions. Without resorting to spin-spin terms or other assumed interactions, the scheme can be realized with a dedicated circuit and a necessary number of quantum dots. Gate fidelity of the quantum computation is also presented.