# Quantum Information Processing

## Quantum Computation

Advances in quantum information processing have opened new avenues for using quantum phenomena to perform computation. Quantum computers have become of great interest, primarily due to their potential of solving certain computationally hard problems such as factoring integers and searching databases. The fact that a quantum computer might be more powerful than an ordinary computer is based on the notion that a quantum system can be in a superposition of states and that this allows exponentially many computations to be done in parallel. The presence of the superposition of states is a direct manifestation of the internal quantum dynamics of the elementary units of the quantum computer, the qubits.
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## Event-by-event simulation of (quantum) optics experiments

Recent advances in nanotechnology are paving the way to attain control over individual microscopic objects. The ability to prepare, manipulate, couple and measure single microscopic systems facilitate the study of single quantum systems at the level of individual events. Such experiments address the most fundamental aspects of quantum theory. One of those aspects is particle-wave duality, a concept of quantum theory that attributes to photons (light quanta) the properties of both wave and particle behavior depending upon the circumstances of the experiment. Together with the Computational Physics group of Groningen we have developed a systematic, modular procedure to construct locally causal, classical (non-Hamiltonian) dynamical systems that can be used for a deterministic or pseudo-random (unpredictable) event-by-event simulation of real-time quantum phenomena, such as quantum interference (double-slit and two-beam experiments, Mach-Zehnder interferometer experiments), universal quantum computation, quantum eraser. Our simulation approach allows the modeling of nanoscale processes on the level of individual events without using concepts of quantum theory.
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## Simulation of quantum systems

Some fundamental questions in statistical mechanics such as under which conditions a system coupled to a reservoir equilibrates and how the canonical distribution emerges from the interaction between the system and the reservoir, have only been partially resolved. Roughly and more generally speaking one could say that the main unresolved question is how the basic equations of physics, which are all deterministic and time-reversible, can give rise to the time-irreversible (thermodynamic) phenomena that we observe.
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