  Carbon nanotubes (CNTs) have attracted much attention for use in
nanomechanical devices because of their exceptional properties, such as large
resonant frequencies, low mass, and high quality factors. Here, we report the
first experimental realization of parametric strong coupling between two
mechanical modes on a single CNT nanomechanical resonator, by applying an extra
microwave pump. This parametric pump method can be used to couple mechanical
modes with arbitrary frequency differences. The properties of the mechanical
resonator are detected by single-electron tunneling at low temperature, which
is found to be strongly coupled to both modes. The coupling strength between
the two modes can be tuned by the pump power, setting the coupling regime from
weak to strong. This tunability may be useful in further phonon manipulations
in carbon nanotubes.
