  The central quantity in the celebrated quantum Jarzynski equality is
$e^{-\beta W}$, where $W$ is work and $\beta$ is the inverse temperature. The
impact of quantum randomness on the fluctuations of $e^{-\beta W}$ and hence on
the predictive power of the Jarzynski estimator is an important problem.
Working on a single nitrogen-vacancy center in diamond and riding on an
implementation of two-point measurement of non-equilibrium work with
single-shot readout, we have conducted a direct experimental investigation of
the relationship between the fluctuations of $e^{-\beta W}$ and adiabaticity of
non-equilibrium work protocols. It is observed that adiabatic processes
minimize the variance of $e^{-\beta W}$, thus verifying an early theoretical
concept, the so-called principle of minimal work fluctuations. Furthermore, it
is experimentally demonstrated that shortcuts-to-adiabaticity control can be
exploited to minimize the variance of $e^{-\beta W}$ in fast work protocols.
Our work should stimulate further experimental studies of quantum effects on
the bias and error in the estimates of free energy differences based on the
Jarzynski equality.
