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Microwave-driven coherent operation of a semiconductor quantum dot charge qubit


An intuitive realization of a qubit is an electron charge at two well-defined positions of a double quantum dot. This qubit is simple and has the potential for high-speed operation because of its strong coupling to electric fields. However, charge noise also couples strongly to this qubit, resulting in rapid dephasing at all but one special operating point called the ‘sweet spot’. In previous studies d.c. voltage pulses have been used to manipulate semiconductor charge qubits1,2,3,4,5,6,7,8 but did not achieve high-fidelity control, because d.c. gating requires excursions away from the sweet spot. Here, by using resonant a.c. microwave driving we achieve fast (greater than gigahertz) and universal single qubit rotations of a semiconductor charge qubit. The Z-axis rotations of the qubit are well protected at the sweet spot, and we demonstrate the same protection for rotations about arbitrary axes in the XY plane of the qubit Bloch sphere. We characterize the qubit operation using two tomographic approaches: standard process tomography9,10 and gate set tomography11. Both methods consistently yield process fidelities greater than 86% with respect to a universal set of unitary single-qubit operations.

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Figure 1: Si/SiGe quantum dot device, qubit spectroscopy and coherent Rabi oscillation measurements.
Figure 2: Ramsey fringes and demonstration of three-axis control of the a.c.-gated charge qubit.
Figure 3: Hahn echo measurement.
Figure 4: QPT and GST of the a.c.-gated charge qubit.


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This work was supported in part by the Army Research Office (W911NF-12-0607), the National Science Foundation (PHY-1104660) and by the Laboratory Directed Research and Development programme at Sandia National Laboratories. Sandia National Laboratories is a multi-programme laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the United States Department of Energy's National Nuclear Security Administration (contract DE-AC04-94AL85000). Development and maintenance of the growth facilities used for fabricating samples is supported by the Department of Energy (DE-FG02-03ER46028). This research utilized National Science Foundation-supported shared facilities at the University of Wisconsin–Madison.

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D.K. performed electrical measurements, state and process tomography, and analysed the data with M.A.E., M.F. and S.N.C. D.R.W. developed the hardware and software for measurements. C.B.S. fabricated the quantum dot device. J.K.G., R.B-K. and E.N. performed gate-set tomography. D.E.S. and M.G.L. prepared the Si/SiGe heterostructure. All authors contributed to the preparation of the manuscript.

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Correspondence to M. A. Eriksson.

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The authors declare no competing financial interests.

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Kim, D., Ward, D., Simmons, C. et al. Microwave-driven coherent operation of a semiconductor quantum dot charge qubit. Nature Nanotech 10, 243–247 (2015).

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