Improved Look-ahead Approaches for Nearest Neighbor Synthesis of 1D Quantum Circuits

In the present era of computation, quantum computing may offer a new direction as it allows to solve certain problems significantly faster than classical solutions. But it also has been found that there are several constrains in performing a successful realization of quantum circuits. One such constraint is the nearest neighbor (NN) criterion which states that qubits which interact with each other have to be adjacent. Motivated by this objective, in this work we propose a linear qubit placement technique that effectively rearranges the qubits and transforms quantum circuits to improved NN-based designs by inserting SWAPs. Furthermore, for placing these SWAPs in appropriate positions, we implemented a look-ahead strategy that considers the effect of the rest of the gates and computes a corresponding impact value which guides the insertion of the SWAP gates. To this extent, we consider three different strategies to evaluate the corresponding "look-ahead effects" and their influence on existing gates. At the end of this work, we have evaluated the developed methodology over a wide range of benchmarks and compared the results with existing related works. In this comparison, we have seen that the proposed technique outperforms the related works and provides substantial reductions in SWAP overhead.