Relativistic Doppler effect in quantum communication

Asher Peres*, Daniel R. Terno

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


When an electromagnetic signal propagates in vacuo, a polarization detector cannot be rigorously perpendicular to the wave-vector because of diffraction effects. The vacuum behaves as a noisy channel, even if the detectors are perfect. The 'noise' can, however, be reduced and nearly cancelled by a relative motion of the observer towards the source. The standard definition of a reduced density matrix fails for photon polarization, because the transversality condition behaves like a superselection rule. We can, however, define an effective reduced density matrix which corresponds to a restricted class of positive operator-valued measures. There are no pure photon qubits and no exactly orthogonal qubit states.

Original languageEnglish
Pages (from-to)1165-1173
Number of pages9
JournalJournal of Modern Optics
Issue number6-7
Publication statusPublished - 15 Apr 2003
Externally publishedYes


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