Two-Electron Quantum Dot Molecule: Composite Particles and the Spin Phase Diagram

Abstract

We study a two-electron quantum dot molecule in a magnetic field by the direct diagonalization of the Hamiltonian matrix. The ground states of the molecule with the total spin S = 0 and S = 1 provide a possible realization for a qubit of a quantum computer. Switching between the states is best achieved by changing the magnetic field. Based on an analysis of the wave function, we show that the system consists of composite particles formed by an electron and flux quanta attached to it. This picture can also be used to explain the spin phase diagram.

Two-electron lateral quantum-dot molecules in a magnetic field

“…The ground state as a function of magnetic field was found to have a highly nontrivial spinphase diagram and a composite-particle structure of the wave function. 12 Also the calculated far-infrared absorption spectra in two-minima QDMs revealed clear deviations from the Kohn modes of a parabolic QD. Surprisingly, the interactions of the electrons smoothened the deviations instead of enhancing them.…”

“…[4][5][6][7][8][9][10][11] Moreover, the lowered symmetry also gives rise to modified ground state properties such as level anticrossings and altered spin-phase diagram as a function of magnetic field. 12,13 After Loss and DiVincenzo proposition, 14 coupled quantum dots have gained interest due to possible realization as spin-qubit based quantum gates in quantum computing. [15][16][17] In addition to coherent single-spin operations, the two-spin operations are sufficient for assembling any quantum computation.…”

“…12,13,18,[26][27][28][29][30][31][32][33] Magnetizations in QDs have been measured indirectly with transport measurements 34 and recently with a direct technique with improved sensitivity. 35 For both measurements, semiclassical approaches cannot explain the results.…”

Electronic correlations in double quantum dots

“…As noted by previous research 4,5,10 , one of the most attractive setup among fewparticle lateral quantum dots is the two-electron case in which the singlet and triplet states can be tuned to be bound into a fourfold degenerate ground state or, depending in the double QD parameters, artificially introducing an energy gap between the singlet and triplet states. This particular characteristic is very similar to that already observed in a two-minima QD subjected to a magnetic field 6 .…”

“…The interest on CQDs in the field of quantum computing was brought over since Loss and DiVincenzo proposal 1 on the possibility of an implementation based on the spin states of coupled single-electron quantum dots. Recent studies and experiments 2,3,4,5,6 have proven the feasibility of using the spin degree of freedom in vertically and laterally coupled few-electron QDs as systems in which interactions can be electro-optically tuned and therefore they can potentially taken as candidates for performing quantum operations.…”