Noise Squeezing And Quantum Entanglement In Near-resonance Driven Systems

Resonance fluorescence lies the heart of quantum optics and laser physics and is a cor-nerstone of exploring the nature of light. The fluorescence field displays squeezing in phase quadrature. For its quadrature squeezing, resonance fluorescence provides a convenient and effective way for generation of squeezed light. On the other hand, one of the phase quadrature has fluctuations below the shot noise without breaking the uncertainty relation. so squeezed light has wide application in light communication. In recent years, quantum information science develops rapidly. Acting as basic resource in quantum information pro-cessing, quantum entanglement attracts more and more attention. Quantum entanglement is a kind of nonlocal and strong quantum correlation in the complex system of two or more subsystems, which can store and transport quantum information. Non-Gaussian entan-glement is required for entanglement distillation and universal quantum computation with continuous variables. We know that resonance fluorescence is typical non-Gaussian light resource. The generation of entanglement in resonance fluorescence may improve quantum communication.1. Trichromatic phase dependence of squeezing in resonance fluorescenceWe calculated the noise spectrum of resonance fluorescence from a two-level atom driven by trichromatic field by quantum regression theorem. Laplace transform and polychromatic harmonic expansion. The result show that the noise spectra have strong dependence on the sun of the relative phases of the sidebands components compared to the central component although the sideband components are much weaker than the central component. When the sun of the relative phases isπ, there is squeezing in the in-phase quadrature at the sideband±(?)((?)=(?)). For the sun of the relative phases is 0, squeezing is no longer exists. The two-photon emission occurs at the sidebandsω0±(?)due to the Stark splitting by the strong central component of driving field. At the same time, the weak sideband components cause the two-photon emission at the same sideband as above. So the squeezing occurs at sideband but not at the central frequency.2. Sideband entanglement in collective resonance fluorescenceThe Mollow sideband in collective resonance fluorescence of two-level atoms driven by strong field can be well separate from the central peck. We consider each sideband as a light field and study the correlation of them. For resonance fluorescence has the non-Gaussian photon statistics with respect to the photon number and so is typical of non-Gaussian light sources. A high order criterion is required to judge the existence of non-Gaussian entanglement in resonance fluorescence. According to the criterion proposed by Shchukin and Vogel and using four-order criterion we show that the non-Gaussian entanglement exists between the two sidebands. The spontaneous parametric process is responsible for the non-Gaussian entanglement.3. High-frequency EPR entanglement via atomic memory effectsAtomic memory effects occur when the atomic relaxation times are comparable to or much longer than the cavity relaxation times. We consider an four-wave mixing ensemble of N four-level atoms in the double A configuration. We show that it is possible to obtain high-frequency Einstein-Podolsky-Rosen entanglement between a pair of Stokes and anti-Stokes fields via atomic memory effects. Since atomic relaxation times are long, the atomic spontaneous emission events have not completed when the cavity fields reach their steady state. So the spontaneous emission can not completely fed back into the cavity fields, quantum fluctuations be suppressed and entanglement be enhanced. The location where the EPR sideband entanglement occurs are determined by ac-Stark splittings of the dressed states due to the signal fields.