  The uncontrolled interaction of a quantum system with its environment is
detrimental for quantum coherence. In the context of solid-state qubits,
techniques to mitigate the impact of fluctuating electric and magnetic fields
from the environment are well-developed. In contrast, suppression of
decoherence from thermal lattice vibrations is typically achieved only by
lowering the temperature of operation. Here, we use a nano-electro-mechanical
system (NEMS) to mitigate the effect of thermal phonons on a solid-state
quantum emitter without changing the system temperature. We study the
silicon-vacancy (SiV) colour centre in diamond which has optical and spin
transitions that are highly sensitive to phonons. First, we show that its
electronic orbitals are highly susceptible to local strain, leading to its high
sensitivity to phonons. By controlling the strain environment, we manipulate
the electronic levels of the emitter to probe, control, and eventually,
suppress its interaction with the thermal phonon bath. Strain control allows
for both an impressive range of optical tunability and significantly improved
spin coherence. Finally, our findings indicate that it may be possible to
achieve strong coupling between the SiV spin and single phonons, which can lead
to the realisation of phonon-mediated quantum gates and nonlinear quantum
phononics.
