  The quantum computation of molecular response properties on near-term quantum
hardware is a topic of significant interest. While computing time-domain
response properties is in principle straightforward due to the natural ability
of quantum computers to simulate unitary time evolution, circuit depth
limitations restrict the maximum time that can be simulated and hence the
extraction of frequency-domain properties. Computing properties directly in the
frequency domain is therefore desirable, but the circuits require large depth
when the typical hardware gate set consisting of single- and two-qubit gates is
used. Here, we report the experimental quantum computation of the response
properties of diatomic molecules directly in the frequency domain using a
three-qubit iToffoli gate, enabling a reduction in circuit depth by a factor of
two. We show that the molecular properties obtained with the iToffoli gate
exhibit comparable or better agreement with theory than those obtained with the
native CZ gates. Our work is among the first demonstrations of the practical
usage of a native multi-qubit gate in quantum simulation, with diverse
potential applications to the simulation of quantum many-body systems on
near-term digital quantum computers.
