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In the first part of the present paper, we have proved that, in order to find an explicit expression for the action, on the [Formula: see text]-orthogonal polynomials, of the 1-parameter unitary groups [Formula: see text] and [Formula: see text], the solution of the inverse normal order problem on the quantum algebra canonically associated to the classical semi-circle random variable is required. In this paper we solve this problem. The solution is obtained in two steps. First we determine the explicit form of normal order in the more general framework of [Formula: see text]-mode-type interacting Fock spaces. Then this result is applied to solve the inverse normal order problem in the semi-circle case.

This paper is a short account of some of the scientific achievements of Wilhelm von Wldenfels with particular attention to the contributions he gave to quantum probability, a field in which he was one of the pioneers.

We investigate the convergence of higher order Cesàro means in Banach spaces. The main results of this paper are: (1) The proof of mean and Birkhoff-type ergodic theorems for higher order Cesàro means. (2) The existence of a one-to-one correspondence between convergent Cesàro means of different orders. (3) The proof of strong laws of large numbers for higher order sums of independent and identically distributed random elements. (4) A characterization of the ergodicity of measure preserving maps in terms of higher order mixing properties. To deal with higher order Cesàro means, one needs a notion of weighted mean more general than the one usually considered in the literature on weighted ergodic theorems. In this context, we also prove a characterization of generalized weighted means preserving Cesàro convergence.

After discussing in general the advantages, for the applications to physics, of deductive models with respect to phenomenological ones, we concentrate on open systems and describe the main ideas of the stochastic limit approach to open systems. We discuss the various levels of the stochastic limit (in increasing order of complexity of the interaction Hamiltonian) describing the new features that emerge at each level and their applications to different branches of physics. We illustrate some examples which highlight how, using the stochastic limit approach, one can answer long-standing questions on various physical behaviors of the composite system solving problems that cannot even be formulated in the reduced evolution (master equation) scheme. In the second part of the paper, we outline the main ideas of the proofs of some of the new features described in the first part. For lack of space, we focus our attention on Level 1 and we have to omit most physical applications. These topics will be the object of a future publication.

In Ref. 3, the quantum Strassen’s theorem has been extended to the infinite-dimensional case. This theorem consists in the solution of the coupling problem for two states on the algebra of bounded operators on two Hilbert spaces [Formula: see text], [Formula: see text] with the additional constraint that the coupling state has support in a pre-assigned sub-space of [Formula: see text]. In this paper, we give an alternative proof of the main theorem in Ref. 3 that allows such extension.

The fact that any classical random variable with all moments has a quantum decomposition allows to associate to it a family of quantum moments. On the other hand, a classical random variable may have several inequivalent quantum decompositions, which lead to the same classical, but different quantum moments. Even in the simplest Central Limit Theorems (CLT), i.e. those of Bernoulli type, there are examples in which the corresponding quantum moments converge to the canonical quantum moments of the associated classical random variable, and examples in which this is not the case. This poses the problem to find a constructive criterium that characterizes the quantum moments associated to the canonical quantum decomposition (which is unique) with respect to the other ones. Theorem [Formula: see text] of the present paper provides such a criterium. Theorem [Formula: see text] deals with the case when one knows a priori that the quantum moments come from a central limit theorem (the motivation of the present paper arose in this context). It gives only a sufficient condition, but simpler to verify than the necessary and sufficient conditions of Theorem [Formula: see text]. Theorem [Formula: see text] naturally leads to a classification of Interacting Fock Spaces (IFS) into three types. We construct examples showing that all these possibilities can effectively take place. On the way, we prove that all the best known deformations of Heisenberg commutation relations can be obtained as special cases of a general construction within the algebraic approach to the theory of orthogonal polynomials.

We prove that, in the framework of generalized quantizations, orthogonality of $$n$$ -particle vectors corresponding to different multi-indexes, together with an additional condition on the norms of $$n$$ -particle vectors characterizes product states. Implications of this result for the non-linear quantization program are discussed.

We classify Bogolyubov endomorphisms of the CCR algebra over a general test function space. This classification requires a non-commutative extension of the usual hyperbolic functions. We consider semi-groups of such endomorphisms and characterize their generators under the assumption of norm continuity.

We propose a quantum extension of the Markov-Dobrushin inequality. As an application, we estimate the Markov-Dobrushin constant for some classes of quantum Markov channels, in particular for the Pauli channel, widely studied in quantum information theory.

We discuss the difference between orthogonal polynomials on finite and infinite dimensional vectors spaces. In particular we prove an infinite dimensional extension of Favard lemma.

After a short review of the quantum mechanics canonically associated with a classical real valued random variable with all moments, we begin to study the quantum mechanics canonically associated to the \textbf{standard semi--circle random variable} $X$, characterized by the fact that its probability distribution is the semi--circle law $\mu$ on $[-2,2]$. We prove that, in the identification of $L^2([-2,2],\mu)$ with the $1$--mode interacting Fock space $\Gamma_{\mu}$, defined by the orthogonal polynomial gradation of $\mu$, $X$ is mapped into position operator and its canonically associated momentum operator $P$ into $i$ times the $\mu$--Hilbert transform $H_{\mu}$ on $L^2([-2,2],\mu)$. In the first part of the present paper, after briefly describing the simpler case of the $\mu$--harmonic oscillator, we find an explicit expression for the action, on the $\mu$--orthogonal polynomials, of the semi--circle analogue of the translation group $e^{itP}$ and of the semi--circle analogue of the free evolution $e^{itP^2/2}$ respectively in terms of Bessel functions of the first kind and of confluent hyper--geometric series. These results require the solution of the \textit{inverse normal order problem} on the quantum algebra canonically associated to the classical semi--circle random variable and are derived in the second part of the present paper. Since the problem to determine, with purely analytic techniques, the explicit form of the action of $e^{-tH_{\mu}}$ and $e^{-itH_{\mu}^2/2}$ on the $\mu$--orthogonal polynomials is difficult, % aaa ask T if it is solved the above mentioned results show the power of the combination of these techniques with those developed within the algebraic approach to the theory of orthogonal polynomials., Comment: 28 pages

The concept of a classical player, corresponding to a classical random variable, is extended to include quantum random variables in the form of self adjoint operators on infinite dimensional Hilbert space. A quantum version of Von Neumann's Minimax theorem for infinite dimensional (or continuous) games is proved.

A new class of public key agreement (PKA) algorithms called strongly-asymmetric algorithms (SAA) was introduced in a previous paper by some of the present authors. This class can be shown to include some of the best-known PKA algorithms, for example the Diffie&ndash, Hellman and several of its variants. In this paper, we construct a new version of the previous construction, called SAA-5, improving it in several points, as explained in the Introduction. In particular, the construction complexity is reduced, and at the same time, robustness is increased. Intuitively, the main difference between SAA-5 and the usual PKA consists of the fact that in the former class, B (Bob) has more than one public key and A (Alice) uses some of them to produce her public key and others to produce the secret shared key (SSK). This introduces an asymmetry between the sender of the message (B) and the receiver (A) and motivates the name for this class of algorithms. After describing the main steps of SAA-5, we discuss its breaking complexity assuming zero complexity of discrete logarithms and the computational complexity for both A and B to create SSK.

A mathematical approach to the notion of complementarity in quantum physics is described and its historical development is shortly reviewed. After that, the notion of n-complementarity is introduced as a natural extension of complementarity and at the same time as weak form of stochastic independence. Several examples in which n-complementarity is realized but not independence are produced. The construction of these examples is based on the structure of Interacting Fock Space (IFS) that is strictly related to the classical theory of orthogonal polynomials. A brief description of both this notion and this connection is included to make the paper self-contained.

The similarity principle is an extension of the principle of thermal relaxation that naturally arises in the stochastic limit of quantum theory. We construct examples of Low Density Limit (LDL) generators, associated to an environment state in equilibrium at inverse temperature β, which admit non-(β, HS)-equilibrium states. We prove that in some cases, the attraction domain of the (β, HS)-equilibrium state is empty. This means that the similarity principle, in its original thermodynamical formulation, can be broken in the LDL limit. This result is obtained as a consequence of a more general phenomenon: the role of degeneracies in the spectrum of the Liouvillian of the system Hamiltonian associated to the generator. We start from the definition of LDL type generators given in [5] and we introduce a finer classification of these generators based on the above degeneracies. The simplest subclass, called 2-generic, is a nontrivial extension of the generators associated to the so-called Λ and V configurations, widely used in quantum optics and involving 2 levels of the system Hamiltonian. Since each 2-generic block involves 3 or 4 levels of the system Hamiltonian we expect that they can reveal some interesting new physical phenomenon, as it happened in the 2-level case. In the last section, we restrict our attention to a 3-level system with a Hamiltonian that is associated to a class of 2-generic LDL generators. Finally, we prove that, for some LDL generators in this class the statement formulated at the beginning holds true.