Quartet states in two-electron quantum dots in bilayer graphene

Trapping electrons in quantum dots and controlling their quantum states is crucial for converting semiconductor structures into bits of quantum information processing. Here, we study single- and two-particle states in electrostatically induced quantum dots in gapped bilayer graphene (BLG), where the electron's valley states appear in a pair with their spin quantum number. Moreover, the features of BLG's electronic structure, such as the three minivalleys around each valley, and the corresponding orbital magnetic moment, modify the characteristics of the dot states. In the weakly gapped case, the single-particle level scheme is that of an almost quadratic band. For a sufficiently strong gap, an additional threefold minivalley degeneracy emerges. Based on these single-particle states, we analyze the orbital, spin, and valley states of two interacting electrons in the dot. We find spin and valley singlets and triplet states depending on the BLG and dot parameters, as well as two-particle interaction strength and external magnetic field. The multiplicity and the spin/valley configuration of the single-and two-particle states are essential for using these degrees of freedom in quantum transport and quantum computing with BLG quantum dot devices.