Ground-state Cooling Of The Mechanical Oscillator And Research Of Continuous Variable EPR Steering In Cavity Optomechanical Systems

Ground state cooling of a NMR has become a hot topic of interesting and important both in theoretical and experimental research fields.Owing to the preparation for a resonator in its ground state not only enables one to exploit its quantum behaviors in the field of quantum technologies,but also has many potential applications in biological sensing,mechanical dis-placement,high-precision detection of gravitational waves and mass,and quantum information processing.On the other hand,due to EPR steering not only enables one to provide a profound insight into quantum physics,but also plays an essential role in quantum information process-ing such as one-side device-independent quantum key distribution,secure quantum teleporta-tion,subchannel discrimination,and quantum imaging and quantum metrology,EPR steering has also become a hot topic of interest and importantance both in theoretical and experimental research fields.Base on the two aspects importance of ground state cooling and EPR steering,the motivations of this paper are mainly based on how to explore better ground cooling scheme and achieve better EPR steering.First of all,we propose a novel scheme for achieving fast cooling a NMR to its ground state by means of transition between two single-polariton states in a hybrid quantum system where a cavity photon mode is coupled to an artificial two-level QD and to a NMR.Distinct from the previous cooling schemes,which require a strong QD-cavity coupling strength,can cancel single-photon excitation process,and just need to drive one of the cavity and the QD with one classical weak laser field.However,by driving the cavity and the QD simultaneously with two classical weak laser fields,the present cooling scheme based on multichannel quantum interference to avoid two-photon excitation of cavity field by modulating the relative phase ?and the Rabi coupling strength ?,it does not require a strong QD-cavity coupling strength,thus this greatly improves the feasibility of experiment.Not only that,in the conventional cooling schemes,the absorption of phonons occur mainly in near-resonance transition between ground state and single-polariton state,it is also required that the driving field strength is weak enough,which results in the cooling rate being often very low.However,here the absorption of phonons occur mainly in resonance transition between two single-polariton states with different energies,it allows the strength of the driving laser field to be relatively strong,thus the cooling rate can be tremendously improved.More importantly,even when the QD-cavity system is in the moderate-coupling regime,ground-state cooling may be achieved with current technology.Second,we study the dissipative dynamics and the formation of entangled states in a driven cascaded quantum network,where a cascaded double-cavity optomechanical system is coupled to a common unidirectional optical fibre.Via feeding broadband vacuum reservior accompa-nying two coherent driving laser fields into the chiral coupling system,the entanglement can be effectively transferred from the light to the two nanomechanical resonator(NMRs)through cavity modes based on the completely destructive interference of quantum noise.By adjusting the relative strength ratio of two red-and blue-detuned pump lasers,it is found that the optimal entanglement exhibits in a perfect EPR entangled mechanical state and two-way EPR steering can also be achieved under certain conditions.If the frequency of the NMR is tuned to be much larger than the chiral coupled cavity chains damping rate,it is demonstrated that the chiral dissi-pative cascaded system can realize one-way steering from one to the other mechanical oscillator while the reverse one-way steering is impossible to obtain.Once again,we explore how to unify perfectly EPR steering and entanglement within the same theoretical framework.We propose a standard form of EPR steering for an arbitrary bipartite Gaussian state under which a simple and efficient steering criterion can be achieved.Based on the same theoretical framework,the standard form and criterion of entanglement can also be obtained and confirmed.It is found that EPR steering requires stronger nonclassical correlations than entanglement while its direction is strictly dependent on mean photon numbers of two light modes.Furthermore,the inherent asymmetric feature and the symmetry can be intuitively embodied in the corresponding criterion,and the essential difference and inherent relation between two standard forms can also be revealed.Finally,we propose a scheme for realizing one-way Gaussian steering between two inter-acting bosonic modes by performing Markovian feedback.It is found that asymmetric steering can be achievable in terms of an unequal beam-splitter and different two feedback loops in the regime of steady states.The conditions for generating steady-state one-way steering are revealed.Furthermore,the entanglement degree and purity of the generated states are also in-vestigated as varying the coupling parameter and the coupling constants as well as the quantum feedback strength.It is shown that the present feedback proposal can simulate a standard two-mode squeezed vacuum environment and a pure steady two-mode squeezed vacuum field can also be obtainable with the perfect detection and a certain level of feedback.