  Response functions are a fundamental aspect of physics; they represent the
link between experimental observations and the underlying quantum many-body
state. However, this link is often under-appreciated, as the Lehmann formalism
for obtaining response functions in linear response has no direct link to
experiment. Within the context of quantum computing, and by using a linear
response framework, we restore this link by making the experiment an
inextricable part of the quantum simulation. This method can be frequency- and
momentum-selective, avoids limitations on operators that can be directly
measured, and is ancilla-free. As prototypical examples of response functions,
we demonstrate that both bosonic and fermionic Green's functions can be
obtained, and apply these ideas to the study of a charge-density-wave material
on ibm_auckland. The linear response method provides a robust framework for
using quantum computers to study systems in physics and chemistry. It also
provides new paradigms for computing response functions on classical computers.
