M. V. Chekhova, F. Ya. Khalili
Polarization quasi-probability distribution (PQPD) is a quasi-probability in the Stokes space, and it enables the calculation of mean values and higher-order moments for polarization observables using simple algebraic averaging. It can be reconstructed with the help of polarization quantum tomography and provides a full description of the polarization properties of quantum states of light. We show here that, due to its definition in terms of the discrete-valued Stokes operators, polarization quasi-probability distribution has singularities and takes negative values at integer values of Stokes observables. However, in experiments with `bright' many-photon states, the photon-number resolution typically is smeared due to the technical limitations of contemporary photodetectors. This results in a PQPD that is positive and regular even for such strongly nonclassical states as single-photon seeded squeezed vacuum. This problem can be solved by `highlighting' the quantum state, that is, by adding a strong coherent beam into the orthogonal polarization mode. This procedure bridges polarization quantum tomography with the Wigner-function tomography, while preserving the main advantage of the first one, namely, immunity to the common phase fluctuations in the light path. Thus, it provides the convenient method for verification of bright nonclassical states of light, such as squeezed Fock states.
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http://arxiv.org/abs/1305.5322
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