Using Hardware Engineering in Quantum Computation: Efficient Circuit Simulation and Reliability Improvement

1. INTRODUCTION In the quantum computational framework there are polynomial time solving algorithms, for problems having exponential classical solutions. The quest is – on one hand – to search if there are other possible effective quantum algorithms and – on the other hand – to be able to produce efficient implementations for the already known algorithms. The most feasible implementation of quantum algorithms is based on the quantum circuit (gate network) model. Our work aims at bridging the gap between classical hardware CAD with design automation techniques, and quantum circuit design rules. This attempt would be extremely difficult without the possibility of an efficient quantum circuit simulation. Thus, our first direction was to try using Hardware Description Languages (HDLs) for simulating quantum circuits, because their property of being able to describe – in a compact manner – the circuit with both structural and behavioral (functional) architectures isolates the inner source of simulation complexity: the entanglement [p1,p2]. Our analysis showed that the probability of simulation improvement just by using the HDL procedure is small. Therefore, we developed a special algorithm for avoiding entangled state representations, the bubble bit technique, which is effective at least when dealing with specific algorithm states [p5]. Our simulation framework has the ability of fault injection, in order to create incentive for validation of quantum circuit fault tolerance strategies and algorithms [p4]. The other direction of this PhD work is finding common ground for reliability techniques and assessment methodologies from the Embryonics project and fault tolerant quantum computation. Embryonics is a biologically inspired reconfigurable hardware project [2], which is suitable for attaining reliability in aggressive, critical environments [p3], similar to quantum computation in terms of fault model and fault occurrence frequency. Adopting the accuracy threshold as reliability measure in Embryonic memories is benefic [p7]. Also, when considering a reconfigurable strategy (reconfigurable quantum gate arrays – rQGAs) in quantum computation fault tolerant stabilizer encoding, the appropriate reliability measure is drastically improved [p6].