title: Microwave-driven coherent operation of a semiconductor quantum dot charge qubit.
abstract: 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 qubits 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 X-Y plane of the qubit Bloch sphere. We characterize the qubit operation using two tomographic approaches: standard process tomography and gate set tomography. Both methods consistently yield process fidelities greater than 86% with respect to a universal set of unitary single-qubit operations.
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: Dohun
authors: D
authors: Kim
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: D R
authors: DR
authors: Ward
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: C B
authors: CB
authors: Simmons
authors: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
authors: John King
authors: JK
authors: Gamble
authors: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
authors: Robin
authors: R
authors: Blume-Kohout
authors: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
authors: Erik
authors: E
authors: Nielsen
authors: Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: D E
authors: DE
authors: Savage
authors: Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: M G
authors: MG
authors: Lagally
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: Mark
authors: 0000000328782844
authors: M
authors: Friesen
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: S N
authors: SN
authors: Coppersmith
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: M A
authors: MA
authors: Eriksson