qubit-ADAPT-VQE: An adaptive algorithm for constructing hardware-efficient ansätze on a quantum processor

Recently, an algorithm termed ADAPT-VQE used fermionic operators to iteratively build system-adapted ansätze with substantially fewer variational parameters compared to other approaches. However, deep state preparation circuits remain a challenge. Here, we present a hardware-efficient variant of this algorithm called qubit-ADAPT. By numerical simulations on H4, LiH and H6, we show that with a well-designed operator pool, qubit-ADAPT can reduce the circuit depth by one order of magnitude while maintaining the same accuracy as its fermionic counterpart. Addressing the high measurement cost which is proportional to the size of the operator pool, we present systematical ways to construct a sufficient pool with size growing linearly in the number of qubits. This result highlights the promise of adaptive simulation algorithms on near-term quantum devices.