Beating the channel capacity limit for linear photonic superdense coding

Julio T. Barreiro, Tzu Chieh Wei, Paul G. Kwiat

Research output: Contribution to journalArticlepeer-review


Dense coding is arguably the protocol that launched the field of quantum communication. Today, however, more than a decade after its initial experimental realization, the channel capacity remains fundamentally limited as conceived for photons using linear elements. Bob can only send to Alice three of four potential messages owing to the impossibility of carrying out the deterministic discrimination of all four Bell states with linear optics, reducing the attainable channel capacity from 2 to log231.585bits. However, entanglement in an extra degree of freedom enables the complete and deterministic discrimination of all Bell states. Using pairs of photons simultaneously entangled in spin and orbital angular momentum, we demonstrate the quantum advantage of the ancillary entanglement. In particular, we describe a dense-coding experiment with the largest reported channel capacity and, to our knowledge, the first to break the conventional linear-optics threshold. Our encoding is suited for quantum communication without alignment and satellite communication.

Original languageEnglish (US)
Pages (from-to)282-286
Number of pages5
JournalNature Physics
Issue number4
StatePublished - Apr 2008

ASJC Scopus subject areas

  • General Physics and Astronomy


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