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Catalin Toma

Publications and source records attributed to Catalin Toma.

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Modeling Quantum Computing with $π$-calculus

Quantum computing is a difficult concept to grasp for computer scientists because it is full of mathematical formulas that have no intuitive meaning related to the problem that the code solves. While these formulae define the way the system behaves, the operational semantics is very far from regular programming languages that reason with variables, assignments, and passing by value the results of computation. This article takes a step back to define a theoretical framework where quantum programs are not treated as sequential programs, but rather as concurrent programs where variables advertise their states through their own channels and code that uses them is reading that state (and possibly collapsing it). The PiQuant framework is a simple extension of the $π$-calculus that contains additional syntax and semantics for the handling of quantum variables.

cs.PL

Geodesic motion in the space-time of a non-compact boson star

We study the geodesic motion of test particles in the space-time of non-compact boson stars. These objects are made of a self-interacting scalar field and -- depending on the scalar field's mass -- can be as dense as neutron stars or even black holes. In contrast to the former these objects do not contain a well-defined surface, while in contrast to the latter the space-time of boson stars is globally regular, can -- however -- only be given numerically. Hence, the geodesic equation also has to be studied numerically. We discuss the possible orbits for massive and massless test particles and classify them according to the particle's energy and angular momentum. The space-time of a boson star approaches the Schwarzschild space-time asymptotically, however deviates strongly from it close to the center of the star. As a consequence, we find additional bound orbits of massive test particles close to the center of the star that are not present in the Schwarzschild case. Our results can be used to make predictions about extreme-mass-ratio inspirals (EMRIs) and we hence compare our results to recent observational data of the stars orbiting Sagittarius A* - the radiosource at the center of our own galaxy.

gr-qc