Laboratoire de Physique Théorique
Toulouse - UMR 5152

In a spin-j system, spin-coherent states are the closest to classical states with a spin pointing along a well defined direction. By contrast, anticoherent spin states are characterized by a vanishing spin expectation value and can be viewed as the most non-classical spin states. In a recent work [1], we have shown that anticoherent spin states are equivalent to maximally entangled symmetric states of a system of N=2j qubits, in the sense that they maximize any entanglement monotone based on linear homogenous positive functions of pure state within their SLOCC classes of states [2,3]. It is therefore important to identify those states as they can serve as a useful resource in many different contexts, especially in quantum information theory. In this talk, we present general conditions, either based on the Husimi function or the Dicke coefficients, for a spin-j state to be anticoherent to any order [4]. We give a nonexistence criterion allowing us to know immediately whether SLOCC classes of symmetric states can contain anticoherent states or not. We analyze the spin-2 or 4-qubit system exhaustively and identify and characterize all anticoherent states of this system.

[1] D. Baguette, T. Bastin, and J. Martin, Phys. Rev. A 90, 032314 (2014). [2] SLOCC Classes : Classes of states equivalent through stochastic local operations with classical communication. [3] F. Verstraete, J. Dehaene, and B. De Moor, Phys. Rev. A 68, 012103 (2003). [4] O. Giraud, D. Braun, D. Baguette, T. Bastin, and J. Martin, Phys. Rev. Lett. 114, 080401 (2015).