  Quantum steering refers to the apparent possibility of exploiting
nonseparable quantum correlations to remotely influence the quantum state of an
observer via local measurements. Different from entanglement and Bell
nonlocality, quantum steering exhibits an inherent asymmetric property, which
makes it relevant for many asymmetric quantum information processing tasks.
Here, we study Gaussian quantum steering between two mechanical modes in an
optomechanical ring cavity. Using experimentally feasible parameters, we show
that the state of the two considered modes can exhibit two-way steering and
even one-way steering. Instead of using unbalanced losses or noises, we propose
a simple practical way to control the direction of one-way steering. A
comparative study between the steering and entanglement of the studied modes
shows that both steering and entanglement undergo a sudden death-like behavior.
In particular, steering is found more fragile against thermal noise remaining
constantly upper bounded by entanglement. The proposed scheme may be meaningful
for one-sided device-independent quantum key distribution, where the security
of such protocol depends fundamentally on the direction of steering.
