Observation of FourPhoton Orbital Angular Momentum Entanglement
Abstract
We demonstrate genuine multipartite quantum entanglement of four photons in their orbital angular momentum degrees of freedom, where a highdimensional discrete Hilbert space is attached to each photon. This can encode more quantum information compared to the qubit case, but it is a longstanding problem to entangle more than two such photons. In our experiment we use pulsed spontaneous parametric downconversion to produce the photon quadruplets, which allows us to detect about one fourphoton event per second. By means of quantum state reconstruction and a suitable witness operator we find that the photon quadruplets form a genuine multipartite entangled symmetric Dicke state. This opens a new tool for addressing foundational questions in quantum mechanics, and for exploration of novel highdimensional multiparty quantum information applications such as secret sharing.
 Publication:

Physical Review Letters
 Pub Date:
 February 2016
 DOI:
 10.1103/PhysRevLett.116.073601
 arXiv:
 arXiv:1508.01480
 Bibcode:
 2016PhRvL.116g3601H
 Keywords:

 Quantum Physics;
 Physics  Optics
 EPrint:
 5 pages, 4 figures