Balanced tripartite entanglement, the alternating group $A_4$\\ and the Lie algebra $sl(3,\mathbb{C})\oplus u(1)$
Michel R. P. Planat
Abstract
I feature three important classes of three-qubit entangled states and their encoding into quantum gates, discrete groups and Lie algebras. States of the GHZ and W-type correspond to pure tripartite and bipartite entanglement, respectively. I introduce another generic class B of three-qubit states, that are equally balanced over two and three parties. I show how to realize the largest cristallographic group $W(E_8)$ in terms of three-qubit gates (with real entries) encoding states of type GHZ or W [M. Planat, {\it Clifford group dipoles and the enactment of Weyl/Coxeter group W(E8) by entangling gates}, Preprint 0904.3691 (quant-ph)]. Then, I describe a peculiar condensation of $W(E_8)$ to the four-letter alternating group $A_4$, obtained from a chain of maximal subgroups. Group $A_4$ is realized from two B-type generators and also corresponds to the Lie algebra $sl(3,\mathbb{C})\oplus u(1)$. Applications are to particle and gravitation physics, and to the genetic code.