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arXiv:quant-ph/0003143

Propagation of entangled light pulses through dispersive and absorbing channels

Alexei Vladimirovich Chizhov, Eduard Schmidt, L. Knöll, D.‐G. Welsch

Published Mar 30, 2000• 0 citations
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Abstract

The modification of initially entangled light pulses passing through dispersive and absorbing four-port devices is studied, using recently obtained results on quantum state transformations [Phys. Rev. A 59, 4716 (1999)]. The fidelity and indices of quantum correlations based on the von Neumann entropy are calculated. Their dependence on both the pulse shape and the four-port device parameters is studied. It is shown, that due to dispersion and absorption the quantum correlations are reduced substantially for large initial entanglement.

DOI
10.48550/arxiv.quant-ph/0003143

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Applying the recently developed formalism of quantum-state transformation of light at absorbing dielectric four-port devices [5], we calculate the quantum state of the outgoing modes of a two-mode squeezed vacuum transmitted through optical fibers of given extinction coefficients. Using the Peres-Horodecki separability criterion for continuous variable systems [4], we then compute both the maximal length of transmission of a two-mode squeezed vacuum through an absorbing system for which the transmitted state is still inseparable and the maximal gain for which inseparability can be observed in an amplifying setup. Finally, we estimate an upper bound of the entanglement preserved after transmission through an absorbing system. The results show that the characteristic length of entanglement degradation drastically decreases with increasing strength of squeezing.
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The behavior of short quantum light pulses propagating in dispersive and absorbing linear ground-state dielectrics is studied, with special emphasis on squeezed pulses. The analysis is based on normally ordered correlation functions of the electric-field strength, which are related to quantities at the entrance plane, on using quantum Langevin equations. Using nonmonochromatic-mode expansion and restricting attention to a single-mode pulse in a squeezed state, the influence on squeezing of the pulse propagation in the medium is discussed in both the time and frequency domains, and it is shown that the noise reduction observable in homodyne detection sensitively depends on the phase control used. Effects, such as squeezing enhancement associated with pulse compression and the destructive influence of the spectral shift caused by absorption, are demonstrated. The numerical results are supplemented by analytical estimations derived for narrow-bandwidth Gaussian pulses. \textcopyright{} 1996 The American Physical Society.