Gate-free VQE Exploiting Inter-qubit Parametric Interaction

As a hybrid quantum simulation algorithm, the variational quantum eigensolver (VQE) leverages both quantum and classical computational resource to construct and evolve a target quantum state. In Ref. [1], a gate-free algorithm termed ctrl-VQE was proposed that achieved chemical accuracy through a direct optimization of the laboratory-frame analog control settings. Here, we present experimental work based on a ctrl-VQE algorithm with two parametrically coupled transmons [2]. The flexibility of parametric interactions between the qubits creates a whole toolbox and enables us to arbitrarily and accurately engineer the inter-qubit coupling in-time and is ideally suited to the ctrl-VQE scheme.

1. Meitei, O.R., et al., “Gate-free state preparation for fast variational quantum eigensolver simulations”, npj Quantum Information, 7, 155, (2021).

2. X. Jin et al., “A versatile parametric coupler between two transmon qubits”, Bulletin of the American Physical Society (2022).