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.

量子操纵是指利用不可分离的量子相关性通过本地测量远程影响观察者的量子态的明显可能性。与纠缠和贝尔非局域性不同，量子转向表现出固有的不对称特性，这使得它与许多不对称量子信息处理任务相关。在这里，我们研究光机械环形腔中两种机械模式之间的高斯量子转向。使用实验上可行的参数，我们表明两种所考虑的模式的状态可以表现出双向转向甚至单向转向。我们提出了一种简单实用的方法来控制单向转向的方向，而不是使用不平衡损耗或噪声。对所研究模式的转向和纠缠之间的比较研究表明，转向和纠缠都会经历类似突然死亡的行为。特别是，我们发现转向对于热噪声来说更加脆弱，因为热噪声始终受到纠缠的限制。所提出的方案对于单方面的设备无关的量子密钥分发可能是有意义的，其中这种协议的安全性从根本上取决于转向的方向。