  Classical rotations of asymmetric rigid bodies are unstable around the axis
of intermediate momentof inertia, causing a flipping of rotor orientation. This
effect, known as the tennis racket effect,quickly averages to zero in classical
ensembles since the flipping period varies significantly uponapproaching the
separatrix. Here, we explore the quantum rotations of rapidly spinning
thermalasymmetric nanorotors and show that classically forbidden tunnelling
gives rise to persistent tennisracket dynamics, in stark contrast to the
classical expectation. We characterise this effect, demon-strating that quantum
coherent flipping dynamics can persist even in the regime where millions
ofangular momentum states are occupied. This persistent flipping offers a
promising route for observ-ing and exploiting quantum effects in rotational
degrees of freedom for molecules and nanoparticles.
