Spin Squeezing Criterion with Local Unitary Invariance

  • Authors:

  • A. R. Usha Devi;Xiaoguang Wang;B. C. Sanders

  • Affiliations:

  • Australian Centre for Quantum Computer Technology, Department of Physics, Macquarie University, Sydney, New South Wales 2109, Australia. Department of Physics, Bangalore University, Jnanabharathi ...;Australian Centre for Quantum Computer Technology, Department of Physics, Macquarie University, Sydney, New South Wales 2109, Australia;Australian Centre for Quantum Computer Technology, Department of Physics, Macquarie University, Sydney, New South Wales 2109, Australia. Quantum Information Science Group, Department of Physics an ...

  • Venue:
  • Quantum Information Processing
  • Year:
  • 2003

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Abstract

We propose a spin squeezing criterion for arbitrary multi-qubit states that is invariant under local unitary operations. We find that, for arbitrary pure two-qubit states, spin squeezing is equivalent to entanglement, and multi-qubit states are entangled if this new spin squeezing parameter is less than unity.PACS: 03.67.-a; 03.65.Ud