arXiv subjects

Abdessatar Souissi

Publications and source records attributed to Abdessatar Souissi.

26 records · Page 2Linked to original sources

arXiv2020

The Hermitian Jacobi process: simplified formula for the moments and application to optical fibers MIMO channels

Using a change of basis in the algebra of symmetric functions, we compute the moments of the Hermitian Jacobi process. After a careful arrangement of the terms and the evaluation of the determinant of an `almost upper-triangular' matrix, we end up with a moment formula which is considerably simpler than the one derived in \cite{Del-Dem}. As an application, we propose the Hermitian Jacobi process as a dynamical model for optical fibers MIMO channels and compute its Shannon capacity for small enough power at the transmitter. Moreover, when the size of the Hermitian Jacobi process is larger than the moment order, our moment formula may be written as a linear combination of balanced terminating ${}_4F_3$-series evaluated at unit argument.

math.PR↗

arXiv2020

A Forward Quantum Markov Field on Graphs

In this paper, we propose a class of quantum Markov fields QMF on a graphs $G= (V,E)$. The Markov structure of the considered QMF is investigated in the finer structure of a quasi-local algebrav $\mathcal{A}_V$ of observables based over a graphs $G$. Namely, the considered Markovian fields are infinite volume states defined through a generating couple $(φ^{(0)}, (\mathcal{E}_{\{y\}\cup N_y}))$ of a product state $φ^{(0)}$ on $\mathcal{A}_V$ and a family of local transition expectations $\mathcal{E}_{\{y\}\cup N_y}$ based on a vertex $y$ and the set of it nearest-neighbors. The main result of the paper concerns the existence and the uniqueness of QMF associated with a couple $(φ^{(0)}, (\mathcal{E}_{\{y\}\cup N_y}))$ for on an important class of graphs including trees strictly.

math-ph↗

arXiv2019

Diagonalizability of quantum Markov States on trees

We introduce quantum Markov states (QMS) in a general tree graph $G= (V, E)$, extending the Cayley tree's case. We investigate the Markov property w.r.t. the finer structure of the considered tree. The main result of this paper concerns the diagonalizability of a locally faithful QMS $φ$ on a UHF-algebra $\mathcal A_V$ over the considered tree by means of a suitable conditional expectation into a maximal abelian subalgebra. Namely, we prove the existence of a Umegaki conditional expectation $\mathfrak E : \mathcal A_V \to \mathcal D_V$ such that $$φ= φ_{\lceil \mathcal D_V}\circ \mathfrak E.$$ Moreover, we clarify the Markovian structure of the associated classical measure on the spectrum of the diagonal algebra $\mathcal D_V$.

math-ph↗

arXiv2019

Quantum Markov States on Cayley trees

It is known that any locally faithful quantum Markov state (QMS) on one dimensional setting can be considered as a Gibbs state associated with Hamiltonian with commuting nearest-neighbor interactions. In our previous results, we have investigated quantum Markov states (QMS) associated with Ising type models with competing interactions, which are expected to be QMS, but up to now, there is no any characterization of QMS over trees. We notice that these QMS do not have one-dimensional analogues, hence results of related to one dimensional QMS are not applicable. Therefore, the main aim of the present paper is to describe of QMS over Cayley trees. Namely, we prove that any QMS (associated with localized conditional expectations) can be realized as integral of product states w.t.r. a Gibbs measure. Moreover, it is established that any locally faithful QMS associated with localized conditional expectations can be considered as a Gibbs state corresponding to Hamiltonians (on the Cayley tree) with commuting competing interactions.

math-ph↗

arXiv2019

Phase Transitions for quantum Ising model with competing XY -interactions on a Cayley tree

The main aim of the present paper is to establish the existence of a phase transition for the quantum Ising model with competing XY interactions within the quantum Markov chain (QMC) scheme. In this scheme, we employ the $C^*$-algebraic approach to the phase transition problem. Note that these kinde of models do not have one-dimensional analogues, i.e. the considered model persists only on trees. It turns out that if the Ising part interactions vanish then the model with only competing XY -interactions on the Cayley tree of order two does not have a phase transition. By phase transition we mean the existence of two distinct QMC which are not quasi-equivalent and their supports do not overlap. Moreover, it is also shown that the QMC associated with the model have clustering property which implies that the von Neumann algebras corresponding to the states are factors.

math-ph↗

arXiv2018

Quantum Markov Chains: A unification approach

In the present paper we study a unified approach for Quantum Markov Chains. A new quantum Markov property that generalizes the old one, is discussed. We introduce Markov states and chains on general local algebras, possessing a generic algebraic property, including both Boson and Fermi algebras. The main result is a reconstruction theorem for quantum Markov chains in the mentioned kind of local algebras. Namely, this reconstruction allows the reproduction of all existing examples of quantum Markov chains and states.

math.OA↗

arXiv2016

Construction of a new class of quantum Markov fields

In the present paper, we propose a new construction of quantum Markov fields on arbitrary connected, infinite, locally finite graphs. The construction is based on a specific tessellation on the considered graph, that allows us to express the Markov property for the local structure of the graph. Our main result concerns the existence and uniqueness of quantum Markov field over such graphs.

math.OA↗

arXiv2016

Phase transitions for Quantum Markov Chains associated with Ising type models on a Cayley tree

The main aim of the present paper is to prove the existence of a phase transition in quantum Markov chain (QMC) scheme for the Ising type models on a Cayley tree. Note that this kind of models do not have one-dimensional analogous, i.e. the considered model persists only on trees. In this paper, we provide a more general construction of forward QMC. In that construction, a QMC is defined as a weak limit of finite volume states with boundary conditions, i.e. QMC depends on the boundary conditions. Our main result states the existence of a phase transition for the Ising model with competing interactions on a Cayley tree of order two. By the phase transition we mean the existence of two distinct QMC which are not quasi-equivalent and their supports do not overlap. We also study some algebraic property of the disordered phase of the model, which is a new phenomena even in a classical setting.

math-ph↗