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Physical model for the electron spin correlation

Ana Marı́a Cetto

Published Aug 17, 2021• 0 citations
OpenAlex

Abstract

The quantum formula for the spin correlation of the bipartite singlet spin state, $C_{Q}(\boldsymbol{a},\boldsymbol{b})$, is derived on the basis of a probability distribution $\rho(\phi)$ that is generic, i. e., independent of $(\boldsymbol{a},\boldsymbol{b})$. In line with a previous result obtained within the framework of the quantum formalism, the probability space is partitioned according to the sign of the product $A=\alpha\beta$ of the individual spin projections $\alpha$ and $\beta$ onto $\boldsymbol{a}$ and $\boldsymbol{b}$; this precludes the transfer of $\alpha$ or $\beta$ from $C_{Q}(\boldsymbol{a},\boldsymbol{b})$ to $C_{Q}(\boldsymbol{a},\boldsymbol{b'})$, for $\boldsymbol{b'}\neq\boldsymbol{b}.$ A specific physical model that reproduces the quantum spin correlation serves to validate our approach.

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The quantum formula for the spin correlation of the bipartite singlet spin state, CQ(a,b)C_{Q}(\boldsymbol{a},\boldsymbol{b})CQ​(a,b), is derived on the basis of a probability distribution ρ(ϕ)\rho(\phi)ρ(ϕ) that is generic, i. e., independent of (a,b)(\boldsymbol{a},\boldsymbol{b})(a,b). In line with a previous result obtained within the framework of the quantum formalism, the probability space is partitioned according to the sign of the product A=αβA=\alpha\betaA=αβ of the individual spin projections α\alphaα and β\betaβ onto a\boldsymbol{a}a and b\boldsymbol{b}b; this precludes the transfer of α\alphaα or β\betaβ from CQ(a,b)C_{Q}(\boldsymbol{a},\boldsymbol{b})CQ​(a,b) to CQ(a,b′)C_{Q}(\boldsymbol{a},\boldsymbol{b'})CQ​(a,b′), for b′≠b.\boldsymbol{b'}\neq\boldsymbol{b}.b′=b. A specific physical model that reproduces the quantum spin correlation serves to validate our approach.
The quantum formula for the spin correlation of the bipartite singlet spin state, CQ(a,b)C_{Q}(\boldsymbol{a},\boldsymbol{b})CQ​(a,b), is derived on the basis of a probability distribution ρ(ϕ)ρ(ϕ)ρ(ϕ) that is generic, i. e., independent of (a,b)(\boldsymbol{a},\boldsymbol{b})(a,b). In line with a previous result obtained within the framework of the quantum formalism, the probability space is partitioned according to the sign of the product A=αβA=αβA=αβ of the individual spin projections ααα and βββ onto a\boldsymbol{a}a and b\boldsymbol{b}b. A specific partitioning and a corresponding set of realizations {$ ϕ$} are associated with every measurement setting (a,b)(\boldsymbol{a},\boldsymbol{b})(a,b); this precludes the transfer of ααα or βββ from CQ(a,b)C_{Q}(\boldsymbol{a},\boldsymbol{b})CQ​(a,b) to CQ(a,b′)C_{Q}(\boldsymbol{a},\boldsymbol{b'})CQ​(a,b′), for b′≠b.\boldsymbol{b'}\neq\boldsymbol{b}.b′=b. A geometric model that reproduces the spin correlation serves to validate our approach, giving a concrete meaning to the quantum result in terms of a (local random variable) probability distribution.
An analysis is made within the quantum formalism of the probabilistic features of the electron spin correlation, with the purpose of clarifying the concepts of contextuality and measurement dependence. The quantum formulas for the spin correlation are then derived on the basis of a probability distribution function and its associated geometric representation, both for a pair of projections of a single-particle spin and for the bipartite system in singlet spin state. This endows the spin correlation with a clear probabilistic meaning and leaves the door open for a possible physical image of the electron spin, as discussed at the end of the paper.
The electron spin correlation is shown to be expressible in terms of a bona fide probability distribution function with an associated geometric representation. With this aim, an analysis is presented of the probabilistic features of the spin correlation within the quantum formalism, which helps clarify the concepts of contextuality and measurement dependence. The dependence of the spin correlation on conditional probabilities allows for a clear separation between system state and measurement context; the latter determines how the probability space should be partitioned in calculating the correlation. A probability distribution function ρ(ϕ) is then proposed, which reproduces the quantum correlation for a pair of single-particle spin projections and is amenable to a simple geometric representation that gives meaning to the variable ϕ. The same procedure is shown to be applicable to the bipartite system in the singlet spin state. This endows the spin correlation with a clear probabilistic meaning and leaves the door open for a possible physical picture of the electron spin, as discussed at the end of the paper.
Abstract. In a recent work, we established a phase-coherent directional amplitude framework that natively reproduces the full spectrum of bipartite quantum correlations, exactly saturating the Tsirelson bound . While that work demonstrated the predictive power of retaining continuous geometric phase information, the structural origin and uniqueness of the underlying signed amplitude distributions remained implicit. In the present paper we show that these distributions are uniquely determined by symmetry and measurement geometry. We propose a geometric interpretation of quantum measurement in which state reduction arises from marginalization over operationally inaccessible degrees of freedom. An arriving particle and a measurement apparatus uniquely determine a plane of relevance, while orthogonal degrees of freedom are physically filtered and marginalized from the effective description. Using harmonic analysis on the sphere, we prove that this geometric marginalization—together with rotational covariance and normalization—uniquely fixes the post-selection amplitude distributions. For spin-½ systems, rotational symmetry restricts the Legendre expansion to its lowest harmonics, forcing the exact signed distribution previously employed. Extended to bipartite product spaces , global rotational invariance uniquely determines the joint amplitude structure that reproduces the standard singlet correlation law. These results provide a kinematic explanation of the amplitude distributions underlying quantum spin correlations and offer a geometric account of quantum state reduction as marginalization over degrees of freedom that are operationally inaccessible to the measurement interaction.