  The temporal dynamics of large quantum systems perturbed weakly by a single
excitation can give rise to unique phenomena at the quantum phase boundaries.
Here, we develop a time-dependent model to study the temporal dynamics of a
single photon interacting with a defect within a large system of interacting
spin qubits (N$>$100). Our model predicts a new quantum resource, giant
susceptibility, when the system of qubits is engineered to simulate a
first-order quantum phase transition (QPT). We show that the absorption of a
single photon pulse by an engineered defect in the large qubit system can
nucleate a single shot quantum measurement through spin noise read-out. This
concept of a single-shot detection event ("click") is different from parameter
estimation which requires repeated measurements. The crucial step of amplifying
the weak quantum signal occurs by coupling the defect to a system of
interacting qubits biased close to a QPT point. The macroscopic change in
long-range order during the QPT generates amplified magnetic noise, which can
be read out by a classical device. Our work paves the way for studying the
temporal dynamics of large quantum systems interacting with a single-photon
pulse.
