Hannover 2016 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 23: Quantum Information: Concepts and Methods IV
Q 23.3: Vortrag
Dienstag, 1. März 2016, 15:00–15:15, e214
Quantumness of spin-1 states — Fabian Bohnet-Waldraff1,2, •Daniel Braun1, and Olivier Giraud2 — 1Institute of theoretical physics, University Tübingen, 72076 Tübingen — 2LPTMS, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
We derive an analytic expression for the quantumness of pure spin-1 states, which measures the degree of non-classicality of a quantum state. Quantumness is defined as the Hilbert-Schmidt distance to the convex hull of SU(2)-coherent states. These spin coherent states play the role of pure classical states, while their convex hull defines the set of mixed classical states. Our formula expresses the quantumness of a state in terms of the smallest eigenvalue of its Bloch matrix. The proof of the formula is based on explicitly constructing the closest classical state. We give numerical evidence that the exact formula for pure states, when evaluated at the smallest eigenvalue of the Bloch matrix of some mixed state, provides an upper bound on the quantumness of that state. Finally, by relating the set of two-qubit symmetric separable states to the set of classical spin-1 states, we make a connection to the theory of entanglement: the quantumness of a pure spin-1 state is linked, through a rather complicated function that we provide explicitly, to the negativity of the state. For mixed states the same function serves as upper bound of the quantumness.