  The prevailing paradigm for plasma turbulence associates a unique stationary
state to given equilibrium parameters. We report the discovery of bistable
turbulence in a strongly magnetised plasma. Two distinct states, obtained with
identical equilibrium parameters in first-principle gyrokinetic simulations,
have turbulent fluxes of particles, momentum and energy that differ by an order
of magnitude, with the low-transport state agreeing with experimental
observations. Occurrences of the two states are regulated by the competition
between an externally imposed mean flow shear and "zonal" flows generated by
the plasma. With small turbulent amplitudes, zonal flows have little impact,
and the mean shear causes turbulence to saturate in a low-transport state. With
larger amplitudes, the zonal shear can (partially) oppose the effect of the
mean shear, allowing the system to sustain a high-transport state. This poses a
new challenge for research that has so far assumed a uniquely defined turbulent
state.
