# Theoretical Physics

**16 February 2017**

**Time:**12:30 to 13:30

**Location:**EC Stoner 7.83

Theoretical Physics Seminar: Jan Sperling (Oxford)

**Entanglement in highly multipartite systems**

Nonlocal quantum correlations had been at the center of the early debates about the validity

of quantum physics. Nowadays, quantum entanglement is believed to be one of the main resources

for applications using quantum technologies and robust schemes to produce inseparable states have

been proposes [1]. Still, the characterization of multipartite entanglement is a challenging problem,

especially, due to the richness of possible correlations between a manifold of subsystems [2].

In this talk, we study different notions of entanglement in systems that consist of many subsystems.

In particular, the detection of such forms of correlations is established using the unique

tool of separability eigenvalue equations [3]. We discuss two experimental implementation of

this technique. In the first experiment, every single partitioning out of 115 974 possible forms

of mode decompositions is demonstrated to be entangled for an experimentally generated, tenmode

frequency-comb state [4]. In the second experiment, a six-mode state of light was prepared

which is biseparable and, at the same time, exhibits entanglement for any other higher-order partitioning.

Finally, we outline the generalization of our approach to infer many-particle entanglement

in compound systems with a non-deterministic, i.e., fluctuating, number of particles [6].

References

[1] J. Metz, M. Trupke, and A. Beige, Phys. Rev. Lett. 97, 040503 (2006).

[2] R. Horodecki, et al., Rev. Mod. Phys. 81, 865 (2009).

[3] J. Sperling and W. Vogel, Phys. Rev. Lett. 111, 110503 (2013).

[4] S. Gerke, et al., Phys. Rev. Lett. 114, 050501 (2015).

[5] S. Gerke, et al., Phys. Rev. Lett. 117, 110502 (2016).

[6] J. Sperling and I. A. Walmsley, arXiv:1611.06028 [quant-ph].

© Copyright Leeds 2011