Mainz 2017 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 23: Quantum Information: Concepts and Methods IV

Q 23.1: Talk

Tuesday, March 7, 2017, 14:30–14:45, P 2

Entanglement and extreme spin squeezing of unpolarized states — •Giuseppe Vitagliano¹, Iagoba Apellaniz¹, Matthias Kleinmann¹, Bernd Lücke⁴, Carsten Klempt⁴, and Geza Toth^1,2,3 — ¹Theoretical Physics, University of the Basque Country UPV/EHU, E-48080 Bilbao, Spain — ²IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain — ³Wigner Research Centre for Physics, H-1525 Budapest, Hungary — ⁴Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany

We present optimal criteria to detect the depth of entanglement in macroscopic ensembles of spin-j particles using the variance and second moments of the collective spin components. The class of states detected goes beyond traditional spin-squeezed states by including Dicke states and other unpolarized states. The criteria derived are easy to evaluate numerically even for systems of very many particles and outperform past approaches, especially in practical situations where noise is present. We also derive analytic lower bounds based on the linearization of our criteria, which make it possible to define spin-squeezing parameters for Dicke states. In addition, we obtain also an analytic lower bound to the condition derived in [A.S. Sorensen and K. Molmer, Phys. Rev. Lett. 86, 4431 (2001)]. We also extend our results to systems with fluctuating number of particles.