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Colloquium – Nick Bonesteel
Quantum Computing with the Exchange Interaction
In exchange-only quantum computation, qubits are encoded using three or more spin-1/2 particles (e.g., electrons in quantum dots) and quantum gates can be performed by switching on and off, or “pulsing,” the isotropic exchange interaction between spins. Finding efficient pulse sequences for realizing two-qubit quantum gates in this way is complicated by the large search space of sequences and has typically involved numerical brute force search. In this talk I will review the current state-of-the-art in exchange-only quantum computation and give a simple analytic derivation of the most efficient known exchange-pulse sequence for carrying out a controlled-NOT gate , originally found numerically by Fong and Wandzura . I will then show how the ideas behind this derivation can be used to analytically find new pulse sequences for two-qubit gates beyond controlled-NOT .
 D. Zeuch and N.E. Bonesteel, PRA 93, 010303 (2016).  B.H. Fong and S.M. Wandzura, Quantum Inf. Comput. 11, 1003 (2011).  D. Zeuch and N.E. Bonesteel, PRB 102.
Host: Chris Stanton