Entanglement And Squeezing Based On Dissipation

Quantum entanglement and squeezing are ones of the key concepts in quantum optics and laser physics. They are beneficial to understand the essential question of quantum mechanics, i.e., realization, localization, hidden variable and so on, and have wide appli-cations in high-precision measurements. The squeezed states are closely related to the entangled states, and they are indispensable resources in quantum information and quan-tum communication networks, and can be used to make quantum dense coding, quantum key distribution, quantum state teleportation and so on. Many schemes for generation of the squeezed and entangled states have been proposed based on the coherent evolution. However, through this way the generated states are easily destroyed since they are fragile to environmental dissipation or decoherence, and the coherence times are shorter than the cavity lifetimes. Recently, Bogoliubov mode dissipation as a different mechanism is proposed for the preparation of squeezed and entangled states. More often than not, one believes that the dissipation is a negative factor for establishing quantum correlations, and so seek to reduce the dissipation as much as possible. However, the Bogoliubov mode dissipation is not the effects of usual vacuum or thermal reservoirs on the individual modes but the effects of engineered reservoirs on the Bogoliubov modes. In principle, once two individual modes combine into the Bogoliubov modes and dissipate predominantly due to the engineered dissipation reservoir, they can be prepared in a squeezed and entan-gled state. Essentially, the Bogoliubov mode dissipation creates the stable two-photon interactions. In this paper, we prepare the squeezed and entangled states based on the Bogoliubov mode dissipation. The innovative contents are shown as follows:First, we present a cavity dissipation scheme to prepare a hybrid system of an atom ensemble and a moving mirror in squeezed and entangled states. This scheme is based on four-wave mixing in the atoms and radiation pressure on the mirror, both of which combine to lead to Bogoliubov interactions of the atoms and the mirror with the cavity fields. Under adiabatic conditions, the cavity fields cause the hybrid Bogoliubov modes to evolve into the vacuum states, which correspond to the two-mode squeezed and entangled states. The dependence of the hybrid entanglement on the system parameters is also presented in and beyond the Bogoliubov interactions. In the previous work, the down-conversion interaction is absent for the atom-cavity subsystem. And the down-conversion interaction between cavity field and the mirror is far off resonance. However, in our scheme the Bogoliubov or alike interactions of the atoms and the mirror with the cavity fields are at resonant sidebands. The cavity fields play a collective dissipation role in the atom-mirror dynamics. This leads to the atoms and the mirror evolving into the squeezed and entangled states.Second, we present dissipation effects on field correlations in two-color interactions with atoms in cavities. We first consider an ensemble of two-level atoms that interacts with the two cavity fields of different frequencies and considerable amplitudes. By transferring the atom-field nonlinearities to the dressed atoms we separate out the interactions of Bogoliubov modes with dressed atoms. The Bogoliubov mode dissipation establishes the stable two-photon processes of two involved fields and therefore leads to two-mode squeezing. As a generalization, we then consider an ensemble of three-level A atoms for double two-color interactions. We extract the Bogoliubov-like four-mode interactions, which establish a quadrilateral of the two-photon processes of four involved fields and thus in four-mode squeezing. We should note the essentially different ways between the monochromatic and bichromatic interactions with atoms for establishing the two-photon processes. For the bichromatic case, the two-photon processes are established by using two fields simultaneously to a single atomic transition. Although the best squeezing is limited to 50%, the parameter range for the squeezing is the almost entire region. However, for the monochromatic case, the two-photon processes are created by using two cascaded atomic transitions, each of which is coupled to one monochromatic field. The squeezing can be enhanced for especial parameters but the parameter range for squeezing is greatly limited.Finally, we present a mechanism for double transparency in an optomechanical sys-tem. This mechanism is based on the coupling of a moving cavity mirror to a second mechanical oscillator. Due to the purely mechanical coupling and the radiation pressure, three pathways are established for excitations of the probe photons into the cavity photon. Destructive interference occurs at two different frequencies, leading to double transparen-cy to the probe field. It is the coupling strength between the mechanical oscillators that determines the locations of the transparency windows. Moreover, the normal splitting appears for the generated Stokes field and the four-wave mixing process is inhibited on resonance. In the previous work, only when the frequencies of the two oscillators simul-taneously interacting with the cavity fields are different, occurs the double transparency. Now in our scheme only the moving mirror interacts with the cavity field and the extra oscillator does not. The two oscillators can have the same frequency. The remarkable feature is the controllable location of the transparency windows.