Laird, Edward A.Taylor, JacobDi Vincenzo, David P.Marcus, CHanson, Micah P.Gossard, Arthur C.2011-09-222010Laird, Edward A., Jacob M. Taylor, David P. Di Vincenzo, Charles M. Marcus, Micah P. Hanson, and Arthur C. Gossard. 2011. Coherent spin manipulation in an exchange-only qubit. Physical Review B, Condensed Matter and Materials Physics 82(7): 075403.1550-235x1098-0121http://nrs.harvard.edu/urn-3:HUL.InstRepos:5139193Initialization, two-spin coherent manipulation, and readout of a three-spin qubit are demonstrated using a few-electron triple quantum dot. The three-spin qubit is designed to allow all operations for full qubit control to be tuned via nearest-neighbor exchange interaction. Fast readout of charge states takes advantage of multiplexed reflectometry. Decoherence measured in a two-spin subspace is found to be consistent with predictions based on gate voltage noise with a uniform power spectrum. The theory of the exchange-only qubit is developed and it is shown that initialization of only two spins suffices for operation. Requirements for full multiqubit control using only exchange and electrostatic interactions are outlined.en-USquantum error-correctionelectron-spincomputationblockadedotsJournal Article2011-09-2210.1103/PhysRevB.82.075403