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A potential experimental system, based on high-stress stoichiometric silicon nitride (Si3N4), is proposed to generate steady-state optomechanical entanglement at room temperature. In the proposed structure, a nanostring interacts dispersively and reactively with a microdisk cavity via the evanescent field. We study the role of both dispersive and reactive couplings in generating optomechanical entanglement, and show that the roomtemperature entanglement can be effectively obtained through the dispersive couplings under the reasonable experimental parameters. In particular, in the limits of high temperature (T) and high mechanical quality factor (Qm), we find that the logarithmic entanglement depends only on the ratio T/Qm. This indicates that improvements of the material quantity and structure design may lead to more efficient generation of stationary high-temperature entanglement. [ABSTRACT FROM AUTHOR]

Quantum metrology with entangled states in realistic noisy environments always suffers from decoherence. Therefore, the measurement precision is greatly reduced. Here we applied the dynamical decoupling method to protect the N-qubit quantum metrology protocol and successfully revived the scaling of the measurement precision as N-κ with κ∊[5/6,11/12]. The degree of the precision revival, as determined by the noise spectrum distribution, indicates that the performance of the protected protocol can be further improved by controlling the noise spectrum. Such a protected protocol is proved to be universal for entanglement-based quantum metrology in the pure dephasing and relaxation noise, which should stimulate the development of practical quantum metrology for weak signal detection of microscopic physics. [ABSTRACT FROM AUTHOR]