Several examples that show the relationship between atomic coherence and entanglement productions have been discussed in this paper. The first example shows how atomic coherence can lead to entanglement between two thermal fields at a temperature T ; In the second example, we demonstrate how a cascade correlated spontaneous emission laser can be used as an entanglement amplifier; The last example illustrates how an arbitrary entangled state of two cavity fields can be prepared through atomic coherence. All these examples seem indicate that the two different quantum effects-coherence and entanglement-are closely related.
In this paper, we discuss the theory of entanglement amplifiers. We first describe non-degenerate optical parametric oscillator as an entanglement amplifier and present an input-output calculation for the entanglement of the output fields. We show that two bright output entanglement beams can be produced from this system. We then show that a correlated spontaneous emission laser can be used to implement an entanglement amplifier.
Possible schemes to implement the basic quantum gates for quantum computation have been presented based on cavity quantum electrodynamics (QED) systems. We then discuss schemes to implement several important quantum algorithms such as the discrete quantum fourier transform (QFT) algorithm and Grover's quantum search algorithm based on these quantum gates. Some other applications of cavity QED based systems including the implementations of a quantum disentanglement eraser and an entanglement amplifier are also discussed.