0409106v3

related topics
{information, entropy, channel}
{vol, operators, histories}
{state, states, entangled}
{error, code, errors}
{theory, mechanics, state}
{states, state, optimal}
{entanglement, phys, rev}
{observables, space, algebra}
{time, decoherence, evolution}
{particle, mechanics, theory}
{let, theorem, proof}
{key, protocol, security}
{operator, operators, space}
{measurement, state, measurements}
{qubit, qubits, gate}
{state, phys, rev}

Channel kets, entangled states, and the location of quantum information

Robert B. Griffiths

abstract: The well-known duality relating entangled states and noisy quantum channels is expressed in terms of a channel ket, a pure state on a suitable tripartite system, which functions as a pre-probability allowing the calculation of statistical correlations between, for example, the entrance and exit of a channel, once a framework has been chosen so as to allow a consistent set of probabilities. In each framework the standard notions of ordinary (classical) information theory apply, and it makes sense to ask whether information of a particular sort about one system is or is not present in another system. Quantum effects arise when a single pre-probability is used to compute statistical correlations in different incompatible frameworks, and various constraints on the presence and absence of different kinds of information are expressed in a set of all-or-nothing theorems which generalize or give a precise meaning to the concept of ``no-cloning.'' These theorems are used to discuss: the location of information in quantum channels modeled using a mixed-state environment; the $CQ$ (classical-quantum) channels introduced by Holevo; and the location of information in the physical carriers of a quantum code. It is proposed that both channel and entanglement problems be classified in terms of pure states (functioning as pre-probabilities) on systems of $p\geq 2$ parts, with mixed bipartite entanglement and simple noisy channels belonging to the category $p=3$, a five-qubit code to the category $p=6$, etc.; then by the dimensions of the Hilbert spaces of the component parts, along with other criteria yet to be determined.

oai_identifier:
oai:arXiv.org:quant-ph/0409106
categories:
quant-ph
comments:
Latex 32 pages, 4 figures in text using PSTricks. Version 3: Minor typographical errors corrected
doi:
10.1103/PhysRevA.71.042337
arxiv_id:
quant-ph/0409106
journal_ref:
Phys. Rev. A 71 (2005) 042337
created:
2004-09-16
updated:
2005-05-26

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