title: Anonymous quantum nonlocality.
abstract: We investigate the phenomenon of anonymous quantum nonlocality, which refers to the existence of multipartite quantum correlations that are not local in the sense of being Bell-inequality-violating but where the nonlocality is--due to its biseparability with respect to all bipartitions--seemingly nowhere to be found. Such correlations can be produced by the nonlocal collaboration involving definite subset(s) of parties but to an outsider, the identity of these nonlocally correlated parties is completely anonymous. For all n≥3, we present an example of an n-partite quantum correlation exhibiting anonymous nonlocality derived from the n-partite Greenberger-Horne-Zeilinger state. An explicit biseparable decomposition of these correlations is provided for any partitioning of the n parties into two groups. Two applications of these anonymous Greenberger-Horne-Zeilinger correlations in the device-independent setting are discussed: multipartite secret sharing between any two groups of parties and bipartite quantum key distribution that is robust against nearly arbitrary leakage of information.
authors.affiliation: Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Yeong-Cherng
authors.initials: YC
authors.lastname: Liang
authors.affiliation: ICFO-Institut de Ciències Fotòniques, 08860 Castelldefels, Barcelona, Spain and Group of Applied Physics, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: Florian John
authors.initials: FJ
authors.lastname: Curchod
authors.affiliation: Department of Theoretical Physics, University of Geneva, 1211 Geneva, Switzerland.
authors.forename: Joseph
authors.initials: J
authors.lastname: Bowles
authors.affiliation: Group of Applied Physics, University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gisin