MaxEnt assisted MaxLik tomography

Maximum likelihood estimation is a valuable tool often applied to inverse problems in quantum theory. Estimation from small data sets can, however, have non unique solutions. We discuss this problem and propose to use Jaynes maximum entropy principle to single out the most unbiased maximum-likelihood guess.Comment: 10 pages, 5 figures, presented at MaxEnt conference in Jackson, WY, 200

Quantum tomography as normalization of incompatible observations

Quantum states are successfully reconstructed using the maximum likelihood estimation on the subspace where the measured projectors reproduce the identity operator. Reconstruction corresponds to normalization of incompatible observations. The proposed approach handles the noisy data corresponding to realistic incomplete observation with finite resolution.Comment: RevTeX, 4 pages, 3 figure

Iterative algorithm for reconstruction of entangled states

An iterative algorithm for the reconstruction of an unknown quantum state from the results of incompatible measurements is proposed. It consists of Expectation-Maximization step followed by a unitary transformation of the eigenbasis of the density matrix. The procedure has been applied to the reconstruction of the entangled pair of photons.Comment: 4 pages, no figures, some formulations changed, a minor mistake correcte

Quantum state estimation

New algorithm for quantum state estimation based on the maximum likelihood estimation is proposed. Existing techniques for state reconstruction based on the inversion of measured data are shown to be overestimated since they do not guarantee the positive definiteness of the reconstructed density matrix.Comment: 4 pages, twocolumn Revte

Quantum theory of incompatible observations

Maximum likelihood principle is shown to be the best measure for relating the experimental data with the predictions of quantum theory.Comment: 3 page

An assessment of service and resource needs of university students with disabilities

Two studies focusing on the need for supportive services and resources for persons with disabilities at universities are described. Both studies took place in the Kitchener-Waterloo community. In Study One, students and faculty at the University of Waterloo and community service workers were surveyed. In Study Two, students and staff at Wilfrid Laurier University and high school students and staff at the Waterloo County Board of Education were surveyed. In total, eighty-two participants were surveyed by interview or questionnaire methods. The results from the two studies provided information about needs and concerns specific to individual participants and settings as well as a number of shared concerns and ideas. From these results, recommendations regarding the future programming of support services and resources into the community, increasing awareness about disability within universities and more globally in the community, and implementing policies and guidelines for the use of special needs services and resources

On the local unitary equivalence of states of multi-partite systems

Two pure states of a multi-partite system are alway are related by a unitary transformation acting on the Hilbert space of the whole system. This transformation involves multi-partite transformations. On the other hand some quantum information protocols such as the quantum teleportation and quantum dense coding are based on equivalence of some classes of states of bi-partite systems under the action of local (one-particle) unitary operations. In this paper we address the question: ``Under what conditions are the two states states, $\varrho$ and $\sigma$, of a multi-partite system locally unitary equivalent?'' We present a set of conditions which have to be satisfied in order that the two states are locally unitary equivalent. In addition, we study whether it is possible to prepare a state of a multi-qudit system. which is divided into two parts A and B, by unitary operations acting only on the systems A and B, separately.Comment: 6 revtex pages, 1 figur