An adaptive pulse-level variational quantum eigensolver

While the Variational Quantum Eigensolver (VQE) is a popular contender for solving molecular electronic states on near-term noisy quantum devices, typical gate-model ansatze for even moderate system sizes tend to result in circuit depth far exceeding the lifetime of present-day qubits. Our ctrl-VQE algorithm abandons the gate-model entirely, instead optimizing the amplitudes, frequencies, and phases of the physical control pulses used to directly manipulate qubit states. Preliminary results simulating transmon devices suggest evolution times can be reduced by several orders of magnitude. We elaborate on these results by comparing adaptive protocols for identifying the minimal number of parameters and pulse duration needed to prepare molecular ground states from a Hartree-Fock reference state.