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arXiv:quant-ph/0105094

A (Classical) Representation for a Spin-S Entity as a compound system in R^3 consisting of 2S Individual Spin-1/2 Entities

Bob Coecke

Published May 19, 2001• 0 citations
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Abstract

We generalize the results of [B. Coecke, Helv. Phys. Acta 68, 396 (1995)] for the representation of coherent states of a spin-1 entity to spin-S entities with S>1 and to non-coherent spin states: through the introduction of 'hidden correlations' (see quant-ph/0105093) we introduce a representation for a spin-S entity as a compound system consisting of 2S 'individual' spin-1/2 entities, each of them represented by a 'proper state', and such that we are able to consider a measurement on the spin-S entity as a measurement on each of the individual spin-1/2 entities. If the spin-S entity is in a maximal spin state, the 2S individual spin-1/2 entities behave as a collection of indistinguishable but separated entities. If not so, we have to introduce the same kind of hidden correlations as required for a hidden correlation representation of a compound quantum systems described by a symmetrical superposition. Moreover, by applying the Majorana representation and Aerts' representation for a spin-1/2 entity, this hidden correlation representation yields a classical mechanistic representation of a spin-S entity in R^3.

DOI
10.48550/arxiv.quant-ph/0105094

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We generalize the results of [B. Coecke, Helv. Phys. Acta 68, 396 (1995)] for the representation of coherent states of a spin-1 entity to spin-S entities with S>1 and to non-coherent spin states: through the introduction of 'hidden correlations' (see quant-ph/0105093) we introduce a representation for a spin-S entity as a compound system consisting of 2S 'individual' spin-1/2 entities, each of them represented by a 'proper state', and such that we are able to consider a measurement on the spin-S entity as a measurement on each of the individual spin-1/2 entities. If the spin-S entity is in a maximal spin state, the 2S individual spin-1/2 entities behave as a collection of indistinguishable but separated entities. If not so, we have to introduce the same kind of hidden correlations as required for a hidden correlation representation of a compound quantum systems described by a symmetrical superposition. Moreover, by applying the Majorana representation and Aerts' representation for a spin-1/2 entity, this hidden correlation representation yields a classical mechanistic representation of a spin-S entity in R^3.
In a recent paper [A. Ahanj et al., Phys. Lett. A368 (2007) 34], we gave a classical protocol to simulate quantum correlations corresponding to the spin-s singlet state for the infinite sequence of spins satisfying 2s + 1 = 2n. In the present paper, we have generalized this result by giving a classical protocols to exactly simulate quantum correlations implied by the spin-s singlet state corresponding to all integer as well as half-integer spin values s. The class of measurements we consider here are only those corresponding to spin observables, as has been done in the above-mentioned paper. The required amount of communication is found to be ⌈ log 2(s + 1)⌉ in the worst case scenario, where ⌈x⌉ is the least integer greater than or equal to x.
An extended Bloch representation of quantum mechanics was recently derived to offer a possible (hidden-measurements) solution to the measurement problem. In this article we use this representation to investigate the geometry of superposition and entangled states, explaining interference effects and entanglement correlations in terms of the different orientations a state-vector can take within the generalized Bloch sphere. We also introduce a tensorial determination of the generators of SU(N), which we show to be particularly suitable for the description of multipartite systems, from the viewpoint of the sub-entities. We then use it to show that non-product states admit a general description where sub-entities can remain in well-defined states, even when entangled. This means that the completed version of quantum mechanics provided by the extended Bloch representation, where density operators are also considered to be representative of genuine states (providing a complete description), not only offers a plausible solution to the measurement problem but also to the lesser-known entanglement problem. This is because we no longer need to give up the general physical principle saying that a composite entity exists and therefore is in a well-defined state, if and only if its components also exist and therefore are also in well-defined states.
We illustrate some problems that are related to the existence of an underlying linear structure at the level of the property lattice associated with a physical system, for the particular case of two explicitly separated spin 1/2 objects that are considered, and mathematically described, as one compound system. It is shown that the separated product of the property lattices corresponding with the two spin 1/2 objects does not have an underlying linear structure, although the property lattices associated with the subobjects in isolation manifestly do. This is related at a fundamental level to the fact that separated products do not behave well with respect to the covering law (and orthomodularity) of elementary lattice theory. In addition, we discuss the orthogonality relation associated with the separated product in general and consider the related problem of the behavior of the corresponding Sasaki projections as partial state space mappings
Simulation of two spin-sss singlet correlations for all sss involving spin measurements
In a recent paper [A. Ahanj et al., quant-ph/0603053], we gave a classical protocol to simulate quantum correlations corresponding to the spin sss singlet state for the infinite sequence of spins satisfying 2s+1=2n2s+1 = 2^{n}2s+1=2n. In the present paper, we have generalized this result by giving a classical protocol to exactly simulate quantum correlations implied by the spin-sss singlet state corresponding to all integer as well as half-integer spin values sss. The class of measurements we consider here are only those corresponding to spin observables, as has been done in the above-mentioned paper. The required amount of communication is found to be ⌈log2(s+1)⌉\lceil {\rm log}_{2} (s + 1) \rceil⌈log2​(s+1)⌉ in the worst case scenario, where ⌈x⌉\lceil x \rceil⌈x⌉ is the least integer greater than or equal to xxx.
The familiar problem of two separated, noninteracting spin- 1/2 particles in a state of zero total spin is analyzed using the consistent history interpretation of quantum mechanics and shown to behave in many respects like a classical system of two noninteracting objects whose individual properties are unknown but strongly correlated with each other. There is no action at a distance between the particles and a measurement on one has no effect whatsoever on the other. However, the result of a measurement of a spin component of one of the particles can be used to infer (correctly) its value prior to the measurement, and also the corresponding spin component of the other particle at all times prior to when that particle interacts with something else. In these respects the quantum system behaves like its classical counterpart. On the other hand, the paradoxical (nonclassical) aspects of the quantum situation seem to be precisely those already present in the quantum theory of a single particle.
We study different notions of quantum correlations in multipartite systems of distinguishable and indistinguishable particles. Based on the definition of quantum coherence for a single particle, we consider two possible extensions of this concept to the many-particle scenario and determine the influence of the exchange symmetry. Moreover, we characterize the relation of multiparticle coherence to the entanglement of the compound quantum system. To support our general treatment with examples, we consider the quantum correlations of a collection of qudits. The impact of local and global quantum superpositions on the different forms of quantum correlations is discussed. For differently correlated states in the bipartite and multipartite scenarios, we provide a comprehensive characterization of the various forms and origins of quantum correlations.