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Physical Review A

Polarization distribution and degree of polarization for three-dimensional quantum light fields

Alfredo Luis

Published Jun 22, 2005• 32 citations
Publisher

Abstract

We introduce a probability distribution for polarization of three-dimensional quantum light fields as a marginal of the quadrature $Q$ function for a three-mode field by removing the variables irrelevant for polarization (total intensity and global phase). The probability distribution turns out to be determined by projection on SU(3) coherent states. We introduce a degree of polarization as the distance between the polarization distribution and the uniform distribution associated with completely unpolarized light. We study the relation between two- and three-dimensional polarization by considering field states with a component in the vacuum state. We apply this formalism to some relevant field states.

DOI
10.1103/physreva.71.063815

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We introduce a probability distribution for polarization of three-dimensional quantum light fields as a marginal of the quadrature QQQ function for a three-mode field by removing the variables irrelevant for polarization (total intensity and global phase). The probability distribution turns out to be determined by projection on SU(3) coherent states. We introduce a degree of polarization as the distance between the polarization distribution and the uniform distribution associated with completely unpolarized light. We study the relation between two- and three-dimensional polarization by considering field states with a component in the vacuum state. We apply this formalism to some relevant field states.
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We study the polarization properties of three-dimensional quantum light fields by using the Stokes operators. We modify the standard definition of degree of polarization in order to encompass polarization properties in the quantum domain. We show that the states with the largest degree of polarization and least polarization fluctuations are the SU(3) coherent states. We show that the standard quadrature coherent states are Poissonian superpositions of SU(3) coherent states. We examine the polarization properties of some other relevant field states.
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It is well established that unpolarized light is invariant with respect to any SU(2) polarization transformation. This requirement fully characterizes the set of density matrices representing unpolarized states. We introduce the degree of polarization of a quantum state as its distance to the set of unpolarized states. We use two different candidates of distance, namely the Hilbert-Schmidt and the Bures metric, showing that they induce fundamentally different degrees of polarization. We apply these notions to relevant field states and we demonstrate that they avoid some of the problems arising with the classical definition.