Optimal Universal Disentangling Machine

Optimal Universal Disentangling Machine for Two Qubit Quantum States

from:
http://adsabs.harvard.edu/abs/1999quant.ph..5036G

to download the paper:
http://arxiv.org/abs/quant-ph/9905036

Sibasish Ghosh, Somshubhro Bandyopadhyay, Anirban Roy, Debasis Sarkar, Guruprasad Kar
(Submitted on 11 May 1999 (v1), last revised 14 Oct 1999 (this version, v4))
We derive the optimal curve satisfied by the reduction factors, in the case of universal disentangling machine which uses only local operations. Impossibility of constructing a better disentangling machine, by using non-local operations, is discussed.


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Disentangling Quantum States while Preserving All Local Properties

http://prl.aps.org/abstract/PRL/v83/i7/p1451_1

Electrical Engineering, UCLA, Los Angeles, California 90095-1594
Received 12 January 1999; published in the issue dated 16 August 1999

We consider here a disentanglement process which transforms a state ρ of two subsystems into an unentangled (i.e., separable) state, while not affecting the reduced density matrix of either subsystem. Recently, Terno [Phys. Rev. A 59, 3320 (1999)] showed that an arbitrary state cannot be disentangled, by a physically allowable process, into a tensor product of its reduced density matrices. In this Letter we show that there are sets of states which can be disentangled, but only into separable states other than the product of the reduced density matrices, and other sets of states which cannot be disentangled at all. Thus, we prove that a universal disentangling machine cannot exist.