Universal quantum simulation with prethreshold superconducting qubits: Single-excitation subspace method

Michael R. Geller, John M. Martinis, Andrew T. Sornborger, Phillip C. Stancil, Emily J. Pritchett, Hao You, and Andrei Galiautdinov
Phys. Rev. A 91, 062309 – Published 8 June 2015

Abstract

Current quantum computing architectures lack the size and fidelity required for universal fault-tolerant operation, limiting the practical implementation of key quantum algorithms to all but the smallest problem sizes. In this work we propose an alternative method for general-purpose quantum computation that is ideally suited for such “prethreshold” superconducting hardware. Computations are performed in the n-dimensional single-excitation subspace (SES) of a system of n tunably coupled superconducting qubits. The approach is not scalable, but allows many operations in the unitary group SU(n) to be implemented by a single application of the Hamiltonian, bypassing the need to decompose a desired unitary into elementary gates. This feature makes large, nontrivial quantum computations possible within the available coherence time. We show how to use a programmable SES chip to perform fast amplitude amplification and phase estimation, two versatile quantum subalgorithms. We also show that an SES processor is well suited for Hamiltonian simulation, specifically simulation of the Schrödinger equation with a real but otherwise arbitrary n×n Hamiltonian matrix. We discuss the utility and practicality of such a universal quantum simulator, and propose its application to the study of realistic atomic and molecular collisions.

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  • Received 18 October 2012

DOI:https://doi.org/10.1103/PhysRevA.91.062309

©2015 American Physical Society

Authors & Affiliations

Michael R. Geller1,*, John M. Martinis2, Andrew T. Sornborger3, Phillip C. Stancil1,4, Emily J. Pritchett1,†, Hao You1,4,5, and Andrei Galiautdinov1

  • 1Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA
  • 2Department of Physics and Google Inc., University of California, Santa Barbara, California 93106, USA
  • 3Department of Mathematics, University of California, Davis, California 95616, USA
  • 4Center for Simulational Physics, University of Georgia, Athens, Georgia 30602, USA
  • 5Department of Chemistry and Physics, Georgia Regents University, Augusta, Georgia 30912, USA

  • *mgeller@uga.edu
  • Current address: HRL Laboratories LLC, 3011 Malibu Canyon Road, Malibu, California 90265, USA.

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Vol. 91, Iss. 6 — June 2015

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