Quantum expanders from any classical Cayley graph expander

  • Authors:
  • Aram W. Harrow

  • Affiliations:
  • Department of Mathematics, University of Bristol, Bristol, U.K.

  • Venue:
  • Quantum Information & Computation
  • Year:
  • 2008

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Abstract

We give a simple recipe for translating walks on Cayley graphs of a group G into a quantum operation on any irrep of G. Most properties of the classical walk carry over to the quantum operation: degree becomes the number of Kraus operators, the spectral gap lower-bounds the gap of the quantum operation (viewed as a linear map on density matrices), and the quantum operation is efficient whenever the classical walk and the quantum Fourier transform on G are efficient. This means that using classical constantdegree constant-gap families of Cayley expander graphs on groups such as the symmetric group, we can construct efficient families of quantum expanders.