Related papers: The four-qubit singlet state and decoherence-free …

This paper has been withdrawn by the author.

This paper is withdrawn by the author. It is superseded by Makhlin's paper quant-ph/0002045.

This paper has been withdrawn by the author, since the author does not have enough time to answer every questions on this result.

This paper has been withdrawn by the author, as it is now incorporated in 0901.4506 (v4)

This paper has been withdrawn by the author.

This paper has been withdrawn by the author.

This paper is withdrawn.

This paper has been withdrawn by the author and replaced by arXiv:0809.4751

This paper has been withdrawn by the authors, due a oversimplified decoherence model. It will be substituted by a new work.

The paper has been withdrawn by the author.

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This paper has been withdrawn by the author because it was a speculative investigation.

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This paper has been withdrawn by the author(s).The scheme presented is insecure.

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The author has withdrawn this submission.

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This paper has been withdrawn.