Pauli graphs when the Hilbert space dimension contains a square: why the Dedekind psi function ?

We study the commutation relations within the Pauli groups built on all decompositions of a given Hilbert space dimension $q$, containing a square, into its factors. Illustrative low dimensional examples are the quartit ($q=4$) and two-qubit ($q=2^2$) systems, the octit ($q=8$), qubit/quartit ($q=2\times 4$) and three-qubit ($q=2^3$) systems, and so on. In the single qudit case, e.g. $q=4,8,12,...$, one defines a bijection between the $\sigma (q)$ maximal commuting sets [with $\sigma[q)$ the sum of divisors of $q$] of Pauli observables and the maximal submodules of the modular ring $\mathbb{Z}_q^2$, that arrange into the projective line $P_1(\mathbb{Z}_q)$ and a independent set of size $\sigma (q)-\psi(q)$ [with $\psi(q)$ the Dedekind psi function]. In the multiple qudit case, e.g. $q=2^2, 2^3, 3^2,...$, the Pauli graphs rely on symplectic polar spaces such as the generalized quadrangles GQ(2,2) (if $q=2^2$) and GQ(3,3) (if $q=3^2$). More precisely, in dimension $p^n$ ($p$ a prime) of the Hilbert space, the observables of the Pauli group (modulo the center) are seen as the elements of the $2n$-dimensional vector space over the field $\mathbb{F}_p$. In this space, one makes use of the commutator to define a symplectic polar space $W_{2n-1}(p)$ of cardinality $\sigma(p^{2n-1})$, that encodes the maximal commuting sets of the Pauli group by its totally isotropic subspaces. Building blocks of $W_{2n-1}(p)$ are punctured polar spaces (i.e. a observable and all maximum cliques passing to it are removed) of size given by the Dedekind psi function $\psi(p^{2n-1})$. For multiple qudit mixtures (e.g. qubit/quartit, qubit/octit and so on), one finds multiple copies of polar spaces, ponctured polar spaces, hypercube geometries and other intricate structures. Such structures play a role in the science of quantum information.Comment: 18 pages, version submiited to J. Phys. A: Math. Theo

Smooth tests of fit for finite mixture distributions

Mixture distributions have become a very flexible and common class of distributions, used in many different applications, but hardly any literure can be found on tests for assessing their goodnes of fit. We propose two types of smooth tests of goodness of fit for mixture distributions. The first test is a genuine smooth test, and the second test makes explicitly use of the mixture structure. In a simulation study the tests are compared to some traditional goodness of fit tests that, however, are not customised for mixture distributions. The first smooth test has overall good power and generally outperforms the other tests. The second smooth test is particularly suitable for assessing the fit of each component distribution separately. The tests are applicable to both continuous and discrete distributions and they are illustrated on three example data sets

Some generalizations of the Anderson-Darling statistic

The Anderson-Darling statistic is basically a weighted average of Pearson statistics. In this paper, we first propose to use other weights and next we generalize the Anderson-Darling statistic by inserting the Cressie-and-Read family of statistics into the Anderson-Darling statistic.Anderson-Darling Goodness-of-fit Sample space partitions

Comparison of some tests of fit for the Laplace distribution

Tests for the Laplace distribution based on the sample skewness and kurtosis coefficients are shown to be related to components of smooth tests of goodness of fit and are compared with a number of tests including the Anderson-Darling test, a new data-driven smooth test, a new empirical characteristic function based test and a new maximum entropy test. This last would be our slight preference as the test of choice for testing for the Laplace distribution.

Collineations of Subiaco and Cherowitzo Hyperovals

A Subiaco hyperoval in PG(2, 2 ), h 4, is known to be stabilised by a group of collineations induced by a subgroup of the automorphism group of the associated Subiaco generalised quadrangle. In this paper, we show that this induced group is the full collineation stabiliser in the case h 2(mod4); a result that is already known for h 2 (mod 4). In addition, we consider a set of 2 + 2 points in PG(2, 2 ), where h 5isodd,whichisaCherowitzo hyperoval for h 15 and which is conjectured to form a hyperoval for all such h. We show that a collineation fixing this set of points and one of the points (0, 1, 0) or (0, 0, 1) must be an automorphic collineation