Fabian Furrer

A special feature of the ground state of a topologically ordered phase is large-scale correlations depending on the topology of the regions. These correlations can be detected by the topological entanglement entropy, or by a measure called the irreducible correlation. In this work, we show that the two measures coincide for states obeying an area law and having zero-correlation length. Moreover, we provide an operational meaning for these measures by proving its equivalence to the optimal rate of a particular class of secret sharing protocols.

The QKD-setup under consideration is comprised of two initially independent squeezed continuous Gaussian states (squeezing 11 dB, anti-squeezing 16 dB) at 1550 nm which become entangled by a 50:50 beam splitter. F. Furrer et al presented a security analysis for the setting we explained above assuming collective and coherent attacks [PRL 109, 100502 (2012)]. We will especially discuss the subtleties of the key generation and propose a new error correction algorithm allowing for the generation of a coherent-attack-secure key in experiment.