"Detecting quantum entanglement in multiparticle systems (notice the new date!!)"

Who: Geza Toth (UPV/EHU Leioa, Ikerbasque)

Place: Donostia International Physics Center (DIPC). Paseo Manuel de Lardizabal, 4, Donostia

Date: Tuesday, 10 February 2015, 12:00

G. Toth (UPV/EHU Leioa, Ikerbasque): Detecting quantum entanglement in
multiparticle systems

The verification of the presence of quantum entanglement is perhaps
one of the most interesting fields in quantum information science [1].
Its importance is due to the fact that entangled states can outperform
non-entangled ones in several quantum information processing
algorithms. Moreover, quantum entanglement is also a resource
even in quantum  metrology [2]. Thus, creating large-scale entanglement
and verifying its presence by simple measurements became
a goal of many recent experiments.

Detecting entanglement is a hard task.  In practice, various
sufficient conditions  for entanglement exist, such as
entanglement witness operators. Some of these conditions can identify not
only entanglement, but also various forms of multipartite entanglement that
can be very useful even when studying the thermal ground states of spin chains.

After reviewing the basics of the field, an example will be shown
where a sufficient condition for entanglement has been used in a
physical system [3]. Concretely, entanglement between many thousands
of neutral atoms has been created in a cold gas experiment. A criterion
developed by us  has been used to estimate the amount of entanglement
based on a measurement of the global spin. It outperforms previous
criteria and applies to a wide class of entangled states.

[1] O. Ghne and G. Tth, Entanglement detection, Phys. Rep. 474, 1 (2009).
[2] G. Tth and I. Apellaniz, Quantum metrology from a quantum
information science perspective,
J. Phys. A: Math. Theor. 47, 424006 (2014), special issue "50 years of
Bell's theorem".
[3] B. Lcke et al., Phys. Rev. Lett. 112, 155304 (2014), Editors'
Suggestion, Synopsis at physics.aps.org.

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