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

Abstract

The effect of an external electric field on the exchange interaction has been studied by an exact diagonalization method for two electrons in laterally coupled quantum dots (QDs). We have performed a systematic study of several nanodevices that contain two gate-defined QDs with different shapes and sizes located between source and drain contacts. The confinement potential is modeled by two potential wells with a variable range and softness. In all the considered nanodevices, the overall dependence of exchange energy J on electric field F is similar, i.e. for low fields J increases with increasing F, while for intermediate fields J reaches a maximum and then abruptly falls to zero if F exceeds a certain critical value. However, the J(F) dependence also shows certain characteristic properties that depend on the nanodevice geometry. We have found that the low- and intermediate-field behavior can be accurately parameterized by a linear function J(F) = αF+β, where α is independent of the nanodevice geometry and softness of the confinement potential. We have shown that the linear J(F) relation appears only if the tunnel coupling between the QDs is weak, i.e. the interdot separation is sufficiently large. This relation becomes nonlinear for the strong interdot coupling. For specific nanodevices we have found that the J(F) dependence exhibits a plateau in a broad electric-field regime. The properties of the exchange energy found in the present paper can be applied to all electrical manipulation of electron spin qubits.

Donor-impurity-related second and third harmonic generation and optical absorption in GaAs-(Ga,Al)As 3D coupled quantum dot-rings under applied electric field

“…Due to their potential technological applications and also to the intrinsic theoretical interest of these artificial atoms and molecules which flexible design turns them into a unique playground to investigate new physics, absent in natural systems. In the situation of laterally coupled QDs different reports have appeared in recent years [4][5][6][7][8][9][10][11], whereas the coupled QR systems are the subject of some research as well [12][13][14]. On the other hand, Zeng and collaborators addressed the particular case of a coupled dot-ring system, also reporting on the nonlinear optical susceptibilities [15].…”

Near-threshold properties of the electronic density of layered quantum dots

“…The coupling of the two quantum dots depends on the spatial extent of the one-electron wave functions, in particular it determines the strength of the exchange interaction between the two electrons. The exchange coupling in double quantum dots has been studied extensively, in particular how it can be tuned using electric fields 21 , magnetic fields 23 , or the effect of the confinement of the double quantum dot in a quantum wire 22 . So, the ability to manipulate the spatial extent of the one electron wave function in an isolated QD, can be decisive when dealing with the states of a double quantum dot.…”

XOR logic gate on electron spin qubits in quadruple coupled quantum dots

“…Fig. 1), U 0 µν is the depth of the potential well (U 0 µν > 0), R µν is the range of the confinement potential that determines the size of QD(µν), r 0 µν is the position of the center of QD(µν), and parameter p ≥ 2 is responsible for the softness of the confinement potential [18]. We consider two model nanodevices, denoted by A and B (Fig.…”

“…Then, the electron gains the additional potential energy ∆U . Taking into account the finite range of electric field F = (F, 0, 0) [18] we put ∆U = −eV and 0 at the right and left electrode, respectively, and ∆U = −eF (x + L/2) in the region between the electrodes, where L is the distance between electrodes e l and e r and F = V /L. The total potential energy U = U c + ∆U of the electron as a function of x and y is displayed in Figs.…”