Fig. 1. Single layer (k = 1) k-muCJ VQE entangler circuit used in this work sketched for M = 4 spatial orbitals or N = 8 qubits. Even (odd) qubits label α (β) spin-orbitals. The circuit consists of a single layer of orbital rotations which are implemented as a series of two-qubit Givens rotations, followed by a layer of diagonal double substitution operators implemented via the four-qubit pair-exchange gate given in eqn (52), followed by another layer of orbital rotations. Note that for the spin-restricted ansatz used here the angles in the Givens gates for α and β spin-orbitals are the same.
