Exploring the Potential Benefits of Alternative Quantum Computing Architectures

Abstract

Noisy intermediate scale quantum (NISQ) computers are becoming a reality thanks to the recent advances made by researchers who physically build such systems. In order to execute corresponding quantum algorithms (usually provided in terms of quantum circuits), certain physical constraints in the architectures need to be satisfied. More precisely, physical constraints restrict the possible interactions between qubits which frequently result in cases where qubits which are supposed to interact in a quantum circuit are not allowed to interact on the physical device. Thus far, this is addressed by dedicated methods that map the logical quantum circuit to a physical realization and satisfy the constraints by inserting further operations. This leads to additional costs which harm the fidelity of the circuit and, hence, urgently need to be avoided. Unfortunately, current state-of-the-art approaches for this mapping process take the existing architectures as invariant and only try to reduce the number of additionally needed operations. In contrast, (slight) changes in the, respectively, given architectures (which still keep the underlying physical constraints satisfied) might be possible and may allow for even better (i.e., less costly) mappings. But this potential has not been investigated yet. In this work, we explore this potential. More precisely, we introduce several schemes for generating alternative coupling graphs (and, by this, quantum computing architectures) that still might be able to satisfy physical constraints but, at the same time, allow for a more efficient realization of the desired quantum functionality. Evaluations confirm the potential of those alternative coupling graphs and demonstrate that they can reduce the mapping overhead by up to 60% in the best case and up to almost 40% on average.