# Erlangen 2018 – wissenschaftliches Programm

## Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

# Q: Fachverband Quantenoptik und Photonik

## Q 68: Quantum Information (Concepts and Methods) V

### Q 68.6: Vortrag

### Freitag, 9. März 2018, 11:45–12:00, K 1.019

**Quantum states with a positive partial transpose are useful for metrology** — •Géza Tóth^{1,2,3} and Tamás Vértesi^{4} — ^{1}Theoretical Physics, University of the Basque Country UPV/EHU, E-48080 Bilbao, Spain — ^{2}IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain — ^{3}Wigner Research Centre for Physics, H-1525 Budapest, Hungary — ^{4}Institute for Nuclear Research, Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen, Hungary

We show that multiparticle quantum states that have a positive partial transpose with respect to all bipartitions of the particles can outperform separable states in linear interferometers. We introduce a powerful iterative method to find such states. We present some examples for multipartite states and examine the scaling of the precision with the particle number. Some bipartite examples are also shown that possess an entanglement very robust to noise. We also discuss the relation of metrological usefulness to Bell inequality violation. We find that quantum states that do not violate any Bell inequality can outperform separable states metrologically. We present such states with a positive partial transpose, as well as with a non-positive positive partial transpose.