Abstract

Continuous variable polarization states have attracted much attention due to their apparent applicability to quantum information networks. Polarization entanglement was first presented by transformation of the well-known quadrature entanglement onto the polarization basis by W. P Bowen et al [1]; the inseparability criteria as well as the EPR paradox criteria for Stokes operators were also demonstrated. We extend the generation of such highly quantum correlated states using the interference of two fiber-based polarization squeezing sources. This squeezing can be efficiently created based on the nonlinear effect (χ⁽³⁾) experienced by ultra-short pulses in fused silica fibers [2]: two linearly orthogonal polarized modes with identical amplitudes propagate through a polarization maintaining fiber, they experience the same nonlinearity and the phase of the interference between them is controlled to achieve circularly polarized light (Ŝ₃ Stokes parameter) at the output. Then the output has a squeezing in the dark “Si-S₂” Stokes operator plane and with a small angle θ_sq to S₁. Polarization entanglement is generated by the interference of two such independent polarization squeezed fields (A, B). As shown in Fig.1, they propagate through the equal-length same-type fibers and have the same optical power after the fiber, thus have the same squeezing angle θ_sq. These beams then interfere on a 49/51 beam splitter with a visibility of ≥98% and the relative phase between the input beams is controlled to π/2. The output beams then remain circularly polarized (denoted as to distinguish from the input fields) and exhibit strong quantum noise correlations in the conjugate pair of Stokes operators in dark plane ( and ) These are measured by properly rotating both the half-wave plates in the measurement setup. When the input fields have polarization squeezing of −4.1 ± 0.2 dB (−3.9 ± 0.2 dB) and anti-squeezing of 19.7 ± 0.1 dB (19.8 ± 0.1 dB), the results of these measurements are given by Fig. 2: the correlation of the squeezing (anti-squeezing) quadrature is −3.3 + 0.2 (−2.8 + 0.2) dB. The sum of these variances gives 0.99 ± 0.02 < 2 which satisfies the inseparability criterion for the polarization variables (Ref. 1 and references therein). The difference between the experimental result and theoretical calculation (0.84 ± 0.04) is explained by imperfections in the production and measurement systems.

© 2007 IEEE