Controlled exchange interaction for quantum logic operations with spin qubits in coupled quantum dots

Abstract

A two-electron system confined in two coupled semiconductor quantum dots is investigated as a candidate for performing quantum logic operations on spin qubits. We study different processes of swapping the electron spins by controlled switching on/off the exchange interaction. The resulting spin swap corresponds to an elementary operation in quantum information processing. We perform a direct time evolution simulations of the time-dependent Schrődinger equation. Our results show that -in order to obtain the full interchange of spins -the exchange interaction should change smoothly in time. The presence of jumps and spikes in the corresponding time characteristics leads to a considerable increase of the spin swap time. We propose several mechanisms to modify the exchange interaction by changing the confinement potential profile and discuss their advantages and disadvantages.

Exchange interaction tuned by electric field in quantum dots

“…Recently, the exchange-interaction induced spin swap operations in coupled QD's have been simulated by a direct solution of a time-dependent Schrödinger equation [2]. Interesting experimental results in the direction of designed manipulation with spin qubits in QD's has been obtained by Petta et al [3] and Elzerman et al [4].…”

Tuning the exchange interaction by an electric field in laterally coupled quantum dots

“…insets of Figs. [2][3][4][5]. The preliminary results for the two circular QD's with the same radius have been presented in paper.…”

“…The results of Figs. [3][4][5] show that parameter α is independent of the confinement potential Ψ|δ(r − r j )|Ψ ,…”

“…If one of the QD's is elliptic (Figs. [3][4][5], the exchange interaction vanishes in the low-field regime, i.e., for 0 ≤ F ≤ F c0 , becomes non-zero at F = F c0 , and increases linearly with F for F c0 ≤ F ≤ F c1 . At F = F c1 the J(F ) dependence exhibits the first cusp, above which J(F ) is nearly constant (cf.…”

“…1,2,3,4 Recently, the exchange-interaction induced spin swap operations in coupled QD's have been simulated by a direct solution of a time-dependent Schrödinger equation. 5 The coherent manipulation of spin qubits in lateral QD's has been studied experimentally by Petta et al, 4 Elzerman et al, 6,7 and Hayashi et al 8 Hatano et al 9 determined the tunnel and exchange couplings in laterally coupled vertical QD's. The quantum logic operations can also be performed in the nanowire double QD's.…”