Is stokes vector can be a quantum state?

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Discussion Overview

The discussion centers around the relationship between the Stokes vector, which describes the polarization state of light, and its potential interpretation as a quantum state. Participants explore whether a Stokes vector can be used to construct a density matrix and the implications of this for measuring polarization.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions if a Stokes four-vector, specifically (1, 1, 0, 0), can be treated as a quantum state and if it can be used to construct a density matrix.
  • Another participant agrees with the initial proposition, stating that the coherency matrix is equivalent to a density matrix.
  • A different participant points out that the coherency matrix is a 2x2 matrix derived from Stokes parameters, while a density matrix constructed from a Stokes vector would be a 4x4 matrix, raising a question about how to measure the degree of polarization from this 4x4 density matrix.
  • Another contribution clarifies that the Stokes vector has four real components and that the coherency matrix is a 2x2 complex matrix, suggesting that one can construct a density matrix from the Stokes vector and vice versa, referencing a textbook for further reading.

Areas of Agreement / Disagreement

Participants express differing views on the dimensionality and implications of using Stokes vectors as quantum states, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are limitations regarding the assumptions made about the relationship between Stokes vectors and density matrices, particularly concerning the dimensions and measurement of polarization.

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Is a stokes four-vector like (1 1 0 0) being horizontal polarized vector can be treated as a quantum state? If the answer is yes, this state can be used to construct density matrix?
 
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But coherency matrix is a 2χ2 matrix, which can be constructed by stokes parameters. The density matrix constructed by stokes vector itself would be a 4χ4 matrix.

ρ=(1 1 0 0)χ(1 1 0 0)

If this 4χ4 matrix is a density matrix, how can I measure the degree of polarization of this density matrix?
 
The Stokes vector has 4 real components.

The coherency matrix is a 2x2 complex matrix built from the unity matrix and the 3 Pauli matricies. That also makes 4 free variables.

You can easily construct the density matrix from the Stokes vector and vice versa. Born and Wolf's textbook has a pretty good chapter on that.
 

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