University of Waterloo

About: University of Waterloo is a education organization based out in Waterloo, Ontario, Canada. It is known for research contribution in the topics: Population & Context (language use). The organization has 36093 authors who have published 93906 publications receiving 2948139 citations. The organization is also known as: UW & uwaterloo.

Experimental quantum cryptography with qutrits

Abstract: We produce two identical keys using, for the first time, entangled trinary quantum systems (qutrits) for quantum key distribution The advantage of qutrits over the normally used binary quantum systems is an increased coding density and a higher security margin The qutrits are encoded into the orbital angular momentum of photons, namely Laguerre–Gaussian modes with azimuthal index l + 1, 0 and −1, respectively The orbital angular momentum is controlled with phase holograms In an Ekert-type protocol the violation of a three-dimensional Bell inequality verifies the security of the generated keys A key is obtained with a qutrit error rate of approximately 10%

Entanglement of Dirac fields in noninertial frames

Abstract: We analyze the entanglement between two modes of a free Dirac field as seen by two relatively accelerated parties. The entanglement is degraded by the Unruh effect and asymptotically reaches a nonvanishing minimum value in the infinite acceleration limit. This means that the state always remains entangled to a degree and can be used in quantum information tasks, such as teleportation, between parties in relative uniform acceleration. We analyze our results from the point of view afforded by the phenomenon of entanglement sharing and in terms of recent results in the area of multiqubit complementarity.

Algebraic design techniques for reliable stabilization

Abstract: In this paper we study two problems in feedback stabilization. The first is the simultaneous stabilization problem, which can be stated as follows. Given plants G_{0}, G_{1},..., G_{l} , does there exist a single compensator C that stabilizes all of them? The second is that of stabilization by a stable compensator, or more generally, a "least unstable" compensator. Given a plant G , we would like to know whether or not there exists a stable compensator C that stabilizes G ; if not, what is the smallest number of right half-place poles (counted according to their McMillan degree) that any stabilizing compensator must have? We show that the two problems are equivalent in the following sense. The problem of simultaneously stabilizing l + 1 plants can be reduced to the problem of simultaneously stabilizing l plants using a stable compensator, which in turn can be stated as the following purely algebraic problem. Given 2l matrices A_{1}, ..., A_{l}, B_{1}, ..., B_{l} , where A_{i}, B_{i} are right-coprime for all i , does there exist a matrix M such that A_{i} + MB_{i} , is unimodular for all i? Conversely, the problem of simultaneously stabilizing l plants using a stable compensator can be formulated as one of simultaneously stabilizing l + 1 plants. The problem of determining whether or not there exists an M such that A + BM is unimodular, given a right-coprime pair ( A, B ), turns out to be a special case of a question concerning a matrix division algorithm in a proper Euclidean domain. We give an answer to this question, and we believe this result might be of some independent interest. We show that, given two n \times m plants G_{0} and G_{1} we can generically stabilize them simultaneously provided either n or m is greater than one. In contrast, simultaneous stabilizability, of two single-input-single-output plants, g 0 and g 1 , is not generic.