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

The variational quantum eigensolver, being a promising algorithm on near-term quantum devices, is extensively used for finding the ground state energy of molecular Hamiltonians. The classical and quantum resources needed by this algorithm, the number of variational parameters in the wavefunction ansatz and the depths of the state preparation circuits, critically depend on the choice of ansatz. Recently, an algorithm termed ADAPT-VQE was introduced to 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, 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 the original ADAPT-VQE. This result highlights the promise of adaptive ansätze algorithms on near-term quantum devices.