Mainz 2017 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 9: Quantum Communication II

Q 9.5: Talk

Monday, March 6, 2017, 18:00–18:15, P 3

Robustness of orbital-angular-momentum photons under perturbations. — •Giacomo Sorelli, Vyacheslav Shatokhin, and Andreas Buchleitner — Physikalisches Institut, Albert-Ludwigs Universität, Freiburg i. Br., Germany

Photons with a helical phase front have a definite orbital angular momentum (OAM) of lℏ, with l an arbitrary integer. Since this spatial degree of freedom spans an infinite-dimensional Hilbert space, it can increase the channel capacity and enhance security of quantum communication. Despite these promising applications, the information encoded in OAM photonic states is fragile with respect to disturbance along the transmission path. In particular, quantum entanglement between photon pairs, which is required for many quantum protocols, rapidly decays when photons propagate through a turbulent atmosphere.

In this talk we compare the robustness of entanglement when encoded in Laguerre Gauss (LG) and Bessel Gauss (BG) modes for two kinds of perturbations. First, we provide an accurate theoretical description of an experiment [1] where entangled biphotons in BG and LG modes were subjected to a circular obstruction. Second, we consider the propagation of such entangled biphotons through a turbulent atmosphere in order to identify which of the two sets of modes is a more resilient one.

[1] M. McLaren et al., Nat. Commun. 5: 3248 (2014)