A nanospintronic universal quantum gate

A simple self-assembled structure has been designed to perform universal 2-qubit operations. This can act as the basic building block of a solid state nanoscale quantum information processor. The gate consists of two tri-layered quantum dots that are electrochemically synthesized within two adjacent pores in a self-assembled porous alumina film. The two outer layers are ferromagnetic metals or semiconductors while the middle layer is a semiconductor with long spin coherence time (e.g. silicon). A single electron is injected into the middle semiconductor layer and its spin encodes a qubit. A target qubit is rotated by first lifting the spin degeneracy of the corresponding electronʹs ground state by applying a transverse potential to induce a Rashba interaction, and then making the spin-splitting energy resonant with a globally applied AC magnetic field. The controlled dynamics of the universal 2-qubit rotation requires exploiting the exchange coupling with the nearest neighboring dot. This coupling makes the spin-splitting energy in the target dot dependent on the spin orientation in the control dot. The ferromagnetic layers act as “polarizers” and “analyzers” for spin injection and detection, thus obviating the need for initialization and also providing a means for reading a qubit.