One-way quantum steering is of importance for quantum technologies, such as secure quantum teleportation. In this paper, we study the generation of one-way quantum steering between two distant yttrium iron garnet (YIG) microspheres in chiral waveguide electromagnonics. We consider that the magnon mode with the Kerr nonlinearity in each YIG sphere is chirally coupled to left- and right-propagating guided photons in the waveguide. We find that quantum steering between the magnon modes is absent with nonchirality but is present merely in the form of one way (i.e., one-way steering) when the chirality occurs. The maximal achievable steering is obviously improved as the chirality degree increases. We further find that when the waveguide's outputs are subjected to continuous homodyne detection, the steering can be considerably enhanced and asymmetric steering with strong entanglement can also be achieved by tuning the chirality. Our study shows that chirality can be explored to effectively realize one-way quantum steering. Compared to other studies on achieving asymmetric steering via controlling intrinsic dissipation, e.g., cavity loss rates, our scheme merely depends on the chirality enabled via positioning the micromagnets in the waveguide and is continuously adjustable and experimentally more feasible.

The coherence and correlation properties of effective bosonic modes of a nanomechanical cavity composed of an oscillating mirror and containing an optical lattice of regularly trapped atoms are studied. The system is modeled as a three-mode system: two orthogonal polariton modes, representing the coupled optical lattice and the cavity mode, and one mechanical mode, representing the oscillating mirror. We examine separately the cases of two-mode and three-mode interactions, which are distinguished by suitable tuning of the mechanical mode to the polariton mode frequencies. In the two-mode case, we find that the occurrence of entanglement in the system is highly sensitive to the presence of first-order coherence between the modes. In particular, the creation of the first-order coherence among the polariton and mechanical modes is achieved at the expense of entanglement between them. In the three-mode case, we show that no entanglement is created between the independent polariton modes if both modes are coupled to the mechanical mode by the parametric interaction. There is no entanglement between the polaritons even if the oscillating mirror is damped by a squeezed vacuum field. The interaction creates first-order coherence between the polaritons, and the degree of coherence can, in principle, be as large as unity. This demonstrates that the oscillating mirror can establish first-order coherence between two independent thermal modes. Further analysis shows that two independent thermal modes can be made entangled in the system only when one of the modes is coupled to the intermediate mode by a parametric interaction and the other is coupled by a linear-mixing interaction.

Einstein-Podolsky-Rosen steering manifests a type of quantum correlations intermediate between entanglement and Bell nonlocality. In this paper we propose a scheme for realizing hybrid atom-mechanical quantum steering in the steady-state regime. In our scheme, an optomechanical two-mode cavity is coupled to a distant ensemble of double-$\lambda$ atoms in a cascade way, which induces the dissipative interaction between the mechanics and the internal atomic states. We show that strong cavity dissipation can lead to two-way atom-mechanical steering and the optimal steering exhibited in an approximate two-mode squeezed-vacuum atom-mechanical state. Moreover, we find that for the present cascade coupling scheme, the one-way steering from the mechanical oscillator to the atoms is achievable under certain conditions, while the reverse one-way steering is impossible to obtain. The reason for achieving the asymmetric steering is analyzed and the effect of mechanical thermal noise on the steering is also studied.

In the paper we study the nonlinear mechanical cooling processes in an intrinsic quadratically optomechanical coupling system without linearizing the optomechanical interaction. We apply scattering theory to calculate the transition rates between different mechanical Fock states using the resolvent of the Hamiltonian, which allows for a direct identification of the underlying physical processes, where only even-phonon transitions are permitted and odd-phonon transitions are forbidden. We verify the feasibility of the approach by comparing the steady-state mean phonon number obtained from transition rates with the simulation of the full quantum master equation, and also discuss the analytical results in the weak coupling limit that coincide with two-phonon mechanical cooling processes. Furthermore, to evaluate the statistical properties of steady mechanical state, we respectively apply the Mandel $Q$ parameter to show that the oscillator can be in nonclassical mechanical states, and the phonon number fluctuations $F$ to display that the even-phonon transitions favor suppressing the phonon number fluctuations compared to the linear coupling optomechanical system.

We propose a scheme to generate four-mode cluster states with four atomic ensembles trapped in single-mode cavities connected by short fibers. With the aid of the cavity dissipation, we find that a four-mode cluster state can be unconditionally created by the simultaneous driving of the ensembles with laser pulses of suitably chosen Rabi frequencies and phases. The scheme could be easily extended to the case of $N$-mode cluster states.