Quantum Information Processing

, Volume 6, Issue 5, pp 381–399 | Cite as

Nonlinear Response and Observable Signatures of Equilibrium Entanglement

  • A. M. Zagoskin
  • A. Yu. Smirnov
  • S. K. Gupta
  • I. S. Slobodov

We investigate how equilibrium entanglement is manifested in the nonlinear response of an N-qubit system. We show that in the thermodynamic limit the irreducible part of the nth-order nonlinear susceptibility indicates that the eigenstates of the system contain entangled (n + 1)-qubit clusters. This opens the way to a directly observable multiqubit entanglement signature. We show that the irreducible part of the static cubic susceptibility of a system of four flux qubits, as a function of external parameters, behaves as a global 4-qubit entanglement measure introduced in Ref. (20). We discuss the possibility of extracting purely-entanglement-generated contribution from the general multipoint correlators in a multiqubit system.


multiqubit entanglement nonlinear susceptibility 


03.67.Mn 03.67.Lx 05.30-d 


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • A. M. Zagoskin
    • 1
    • 2
  • A. Yu. Smirnov
    • 2
    • 3
  • S. K. Gupta
    • 1
  • I. S. Slobodov
    • 1
  1. 1.Department of Physics and AstronomyThe University of British ColumbiaVancouverCanada
  2. 2.Digital Materials Lab.Frontier Research System, RIKENWako-shiJapan
  3. 3.CREST, Japan Science and Technology AgencyKawaguchiJapan

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