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Algorithm-Aware Qubit Mapping
  • Yanjun Ji ,
  • Ilia Polian
Yanjun Ji
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Ilia Polian
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Abstract

Algorithm-Aware (AlgAw) qubit mapping aims at directly providing the solutions to qubit mapping of algorithms with regular structures based on the algorithm’s features. Although the exact method provides a high-quality solution, its compilation time grows exponentially with the circuit size. To improve its scalability, we propose the AlgAw qubit mapping. The main idea is to first determine the subcircuits in an algorithm to be mapped, then analyze the optimal solutions of small-scale subcircuits found by exact methods to obtain solutions of large-scale subcircuits, and finally reconstruct the entire circuit and assign parameters. Applying AlgAw to the Quantum Approximate Optimization Algorithm (QAOA) on linear and T-shaped subtopologies produces optimal and scalable solutions for arbitrary numbers of qubits and depths, which is critical to the algorithm’s performance on Noisy Intermediate-Scale Quantum (NISQ) computers. Compared to Qiskit, Tket, and SWAP-Network, AlgAw produces the least number of CNOT gates and the lowest circuit depth. Furthermore, AlgAw takes only a few seconds to obtain a circuit with a hundred qubits that satisfies the connectivity constraints. The benchmarking results on Quantum Processing Units (QPUs) show that AlgAw qubit mapping yields higher values of approximation ratio than others. AlgAw can also be applied to other algorithms such as the Variational Quantum Eigensolver (VQE).