%0 Journal Article
%J Physical Review Letters
%D 2013
%T Electrically-protected resonant exchange qubits in triple quantum dots
%A J. M. Taylor
%A V. Srinivasa
%A J. Medford
%X We present a modulated microwave approach for quantum computing with qubits comprising three spins in a triple quantum dot. This approach includes single- and two-qubit gates that are protected against low-frequency electrical noise, due to an operating point with a narrowband response to high frequency electric fields. Furthermore, existing double quantum dot advances, including robust preparation and measurement via spin-to-charge conversion, are immediately applicable to the new qubit. Finally, the electric dipole terms implicit in the high frequency coupling enable strong coupling with superconducting microwave resonators, leading to more robust two-qubit gates.
%B Physical Review Letters
%V 111
%8 2013/7/31
%G eng
%U http://arxiv.org/abs/1304.3407v2
%N 5
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.111.050502
%0 Journal Article
%J Physical Review Letters
%D 2013
%T The Resonant Exchange Qubit
%A J. Medford
%A J. Beil
%A J. M. Taylor
%A E. I. Rashba
%A H. Lu
%A A. C. Gossard
%A C. M. Marcus
%X We introduce a solid-state qubit in which exchange interactions among confined electrons provide both the static longitudinal field and the oscillatory transverse field, allowing rapid and full qubit control via rf gate-voltage pulses. We demonstrate two-axis control at a detuning sweet-spot, where leakage due to hyperfine coupling is suppressed by the large exchange gap. A {\pi}/2-gate time of 2.5 ns and a coherence time of 19 {\mu}s, using multi-pulse echo, are also demonstrated. Model calculations that include effects of hyperfine noise are in excellent quantitative agreement with experiment.
%B Physical Review Letters
%V 111
%8 2013/7/31
%G eng
%U http://arxiv.org/abs/1304.3413v2
%N 5
%! Phys. Rev. Lett.
%R 10.1103/PhysRevLett.111.050501
%0 Journal Article
%J Nature Nanotechnology
%D 2013
%T Self-Consistent Measurement and State Tomography of an Exchange-Only Spin Qubit
%A J. Medford
%A J. Beil
%A J. M. Taylor
%A S. D. Bartlett
%A A. C. Doherty
%A E. I. Rashba
%A D. P. DiVincenzo
%A H. Lu
%A A. C. Gossard
%A C. M. Marcus
%X We report initialization, complete electrical control, and single-shot readout of an exchange-only spin qubit. Full control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in under 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements, and non-orthogonal control axes.
%B Nature Nanotechnology
%V 8
%P 654 - 659
%8 2013/9/1
%G eng
%U http://arxiv.org/abs/1302.1933v1
%N 9
%! Nature Nanotech
%R 10.1038/nnano.2013.168