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Design of strongly modulating pulses to implement precise effective Hamiltonians for quantum information processing

J. Chem. Phys. 116, 7599 (2002); doi:10.1063/1.1465412

Issue Date: 1 May 2002

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Evan M. Fortunato, Marco A. Pravia, and Nicolas Boulant
Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Grum Teklemariam
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Timothy F. Havel and David G. Cory
Department of Nuclear Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
We describe a method for improving coherent control through the use of detailed knowledge of the system's Hamiltonian. Precise unitary transformations were obtained by strongly modulating the system's dynamics to average out unwanted evolution. With the aid of numerical search methods, pulsed irradiation schemes are obtained that perform accurate, arbitrary, selective gates on multiqubit systems. Compared to low power selective pulses, which cannot average out all unwanted evolution, these pulses are substantially shorter in time, thereby reducing the effects of relaxation. Liquid-state nuclear magnetic resonance techniques on homonuclear spin systems are used to demonstrate the accuracy of these gates both in simulation and experiment. Simulations of the coherent evolution of a three-qubit system show that the control sequences faithfully implement the unitary operations, typically yielding gate fidelities on the order of 0.999 and, for some sequences, up to 0.9997. The experimentally determined density matrices resulting from the application of different control sequences on a three-spin system have overlaps of up to 0.99 with the expected states, confirming the quality of the experimental implementation. ©2002 American Institute of Physics.
History: Received 24 August 2001; accepted 6 February 2002
Permalink: http://link.aip.org/link/?JCPSA6/116/7599/1
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KEYWORDS and PACS

Keywords
PACS
  • 03.67.-a
    Quantum mechanics, field theories, and special relativity Quantum information
  • YEAR: 2002

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0021-9606 (print)   1089-7690 (online)
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