Characterization of Multipartite Entanglement for One Photon Shared Among Four Optical Modes

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Science  08 May 2009:
Vol. 324, Issue 5928, pp. 764-768
DOI: 10.1126/science.1172260

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Entanglement Sharing

Quantum information processing relies on the ability to generate quantum states, to entangle them, and to send and receive those quantum states reliably across networks. With quantum two-level systems, or qubits, if you want to have a large system (and solve complex problems), there is a fear that the ancillary equipment required to control the system will increase rapidly, perhaps too quickly. The use of multipartite systems, where several quantum states can be accessed in a single component, has been proposed as a solution. Papp et al. (p. 764) work with a multipartite system consisting of a single photon shared between four optical modes and show that the degree of entanglement can be controllably tuned. The ability to work with, and control, such entangled multipartite systems should help the development of quantum information processing.


Access to genuine multipartite entanglement of quantum states enables advances in quantum information science and also contributes to the understanding of strongly correlated quantum systems. We report the detection and characterization of heralded entanglement in a multipartite quantum state composed of four spatially distinct optical modes that share one photon, a so-called W state. By randomizing the relative phase between bipartite components of the W state, we observed the transitions from four- to three- to two-mode entanglement with increasing phase noise. These observations are possible for our system because our entanglement verification protocol makes use of quantum uncertainty relations to detect the entangled states that span the Hilbert space of interest.

  • * These authors contributed equally to this work.

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