Quantum manipulation of cavity fields using atomic coherence and entanglement

Abstract

We study manipulation of cavity fields via interaction between a cavity field and atoms. Firstly, we give theoretical analysis of a cavity field which interacts with a four-level double-$\Lambda$ atom. While the cavity field interacts with two atomic transitions, two other atomic transitions are driven by two classical fields. It is found that our system always works as a phase sensitive linear amplifier with no window for a phase insensitive linear amplifier. We also show that the system behaves as a two-photon correlated emission laser under certain conditions. Secondly, theoretical analysis is given of an experimental scheme that can perform individual photon operations such as the photon annihilation operation $\alpha$, creation operation $a^{\dag}$ and commutation operation $\alpha\alpha^{\dagger}$-$\alpha\alpha^{\dagger}$, utilizing atom-cavity field interactions and conditional measurements. In order for the scheme to perform the desired photon operation, the atom-cavity field interaction times are generally required to be sufficiently short that photon annihilation and/or creation are dominated by the one-half Rabi cycle process. Such short interaction times, however, lead inevitably to a low success probability of the scheme. It is shown that this problem of low success probability can be overcome by preparing the cavity field in a superposition of a small number(two) of Fock states and choosing the interaction times appropriately. We also address the problem of validating the value of the commutator for which we can assume $[$\alpha,\alpha^{\dagger}$]=$\It{K}$$. We present a scheme to determine the value of $\It{K}$ using the interaction of an initially excited two level atom with the cavity field and the conditional probability for the atom to remain excited after the interaction.