  The newly established Heisenberg limit in arbitrary waveform estimation is
quite different with parameter estimation and shows a unique characteristic of
a future quantum version of oscilloscope. However, it is still a non-trivial
challenge to generate a large number of exotic quantum entangled states to
achieve this quantum limit. Here, by employing the time-domain quantum
difference detection method, we demonstrate Heisenberg-limited waveform quantum
estimation with diamond spins under ambient condition in the experiment.
Periodic dynamical decoupling is applied to enhance both the dynamic range and
sensitivity by one order of magnitude. Using this quantum-enhanced estimation
scheme, the estimation error of an unknown waveform is reduced by more than $5$
dB below the standard quantum limit with $N\sim{\text{2}} \times
{\text{1}}{{\text{0}}^3}$ resources, where more than ${1 \times
{\text{1}}{{\text{0}}^5}}$ resources would be required to achieve a similar
error level using classical detection. This work provides an essential step
towards realizing quantum-enhanced structure recognition in a continuous space
and time.
