Exchange Interaction Between Three and Four Coupled Quantum Dots: Theory and Applications to Quantum Computing

摘要

Several prominent proposals have suggested that spins of localized electronscould serve as quantum computer qubits. The exchange interaction has beeninvoked as a means of implementing two qubit gates. In this paper, we analyzethe strength and form of the exchange interaction under relevant conditions. Wefind that, when several spins are engaged in mutual interactions, thequantitative strengths or even qualitative forms of the interactions canchange. It is shown that the changes can be dramatic within a Heitler-Londonmodel. Hund-Mulliken calculations are also presented, and support thequalititative conclusions from the Heitler-London model. The effects need to beconsidered in spin-based quantum computer designs, either as a source of gateerror to be overcome or a new interaction to be exploited.