# Entanglement transformation at absorbing and amplifying four-port devices

Authors
Type
Published Article
Publication Date
Sep 11, 2000
Submission Date
Apr 02, 2000
Identifiers
DOI: 10.1103/PhysRevA.62.043803
arXiv ID: quant-ph/0004003
Source
arXiv
Dielectric four-port devices play an important role in optical quantum information processing. Since for causality reasons the permittivity is a complex function of frequency, dielectrics are typical examples of noisy quantum channels, which cannot preserve quantum coherence. To study the effects of quantum decoherence, we start from the quantized electromagnetic field in an arbitrary Kramers--Kronig dielectric of given complex permittivity and construct the transformation relating the output quantum state to the input quantum state, without placing restrictions on the frequency. We apply the formalism to some typical examples in quantum communication. In particular we show that for entangled qubits the Bell-basis states $|\Psi^\pm>$ are more robust against decoherence than the states $|\Phi^\pm>$.