A successive approximation method for quantum separability

Deren Han, Liqun Qi

Research output: Journal article publicationJournal articleAcademic researchpeer-review

9 Citations (Scopus)


Determining whether a quantum state is separable or inseparable (entangled) is a problem of fundamental importance in quantum science and has attracted much attention since its first recognition by Einstein, Podolsky and Rosen [Phys. Rev., 1935, 47: 777] and Schrödinger [Naturwissenschaften, 1935, 23: 807-812, 823-828, 844-849]. In this paper, we propose a successive approximation method (SAM) for this problem, which approximates a given quantum state by a so-called separable state: if the given states is separable, this method finds its rank-one components and the associated weights; otherwise, this method finds the distance between the given state to the set of separable states, which gives information about the degree of entanglement in the system. The key task per iteration is to find a feasible descent direction, which is equivalent to finding the largest M-eigenvalue of a fourth-order tensor. We give a direct method for this problem when the dimension of the tensor is 2 and a heuristic cross-hill method for cases of high dimension. Some numerical results and experiences are presented.
Original languageEnglish
Pages (from-to)1275-1293
Number of pages19
JournalFrontiers of Mathematics in China
Issue number6
Publication statusPublished - 1 Dec 2013


  • cross-hill
  • entanglement
  • M-eigenvalue
  • Quantum system
  • successive approximation
  • tensor

ASJC Scopus subject areas

  • Mathematics (miscellaneous)


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