0407227v3

related topics
{state, states, entangled}
{let, theorem, proof}
{bell, inequality, local}
{states, state, optimal}
{classical, space, random}
{measurement, state, measurements}
{vol, operators, histories}
{qubit, qubits, gate}
{group, space, representation}
{operator, operators, space}
{temperature, thermal, energy}
{algorithm, log, probability}
{observables, space, algebra}
{key, protocol, security}

Compatibility of subsystem states

Paul Butterley, Anthony Sudbery, Jason Szulc

abstract: We examine the possible states of subsystems of a system of bits or qubits. In the classical case (bits), this means the possible marginal distributions of a probability distribution on a finite number of binary variables; we give necessary and sufficient conditions for a set of probability distributions on all proper subsets of the variables to be the marginals of a single distribution on the full set. In the quantum case (qubits), we consider mixed states of subsets of a set of qubits; in the case of three qubits, we find quantum Bell inequalities -- necessary conditions for a set of two-qubit states to be the reduced states of a single mixed state of three qubits. We conjecture that these conditions are also sufficient.

oai_identifier:
oai:arXiv.org:quant-ph/0407227
categories:
quant-ph
comments:
19 pages, LaTeX. In memoriam Asher Peres. Substantial revision: one theorem removed, one author added
arxiv_id:
quant-ph/0407227
journal_ref:
Found. Phys. 36, 83-101 (2006)
created:
2004-07-28
updated:
2005-04-22

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