Radiation of Atoms in a Resonant Environment

Omar Qisieh, Rahma Abdelmagid, Gehad Sadiek

We study the entanglement dynamics of a pair of non-identical interacting atoms (qubits) coupled off-resonance to a single-mode cavity radiation field and exposed to dephasing environments. The qubits are studied starting from various initial states that are disentangled from an initially coherent field. The system models the basic building units of quantum information processing (QIP) platforms under the realistic considerations of asymmetry and external environmental influences. We investigate how introducing a radiation field alters the system's entanglement dynamics in the presence of dephasing environments, and how it impacts the effects of the dephasing environments themselves. The work examines the problem under various settings of inter-qubit interactions, which are now experimentally controllable in some of the newly engineered artificial qubit systems. We illustrate that only upon introducing the radiation field, the system suffers a terminal disentanglement (followed by no revivals) in a finite time. This behavior is exacerbated when the atoms' interaction with the field is stronger. Moreover, the effects of the field's intensity and the atoms' detunings are vastly sensitive to the choice of the initial state. We also demonstrate that the closer the atoms' transition frequencies are to resonance with the field, the more pronounced are the effects of strengthening the independent dephasing environments corresponding to some initial states. Those states also suffered a greater reduction in entanglement content when the qubits with stronger atom-field interaction strength were influenced by a stronger independent dephasing environment. In addition, we examined the ability of the correlated dephasing environment to induce a noise-enhanced efficiency in the presence of an external radiation field. We showed that the radiation field could play a decisive role in enabling or restricting noise-enhanced efficiency, but one that is also highly sensitive to the system's initial state.

W. Russell Hindmarsh

Yoshimasa Isawa

Using a tight binding approach, the Green's function for radiation fields ( R F ) in a resonator is calculated by considering that they are interacting with a vacuum field in an external environment outside the resonator. The general formulas for the rates of the spontaneous and stimulated emission from an atom in an excited state are given, of which the latter is evaluated for an initial state with only one photon. The emission rate is obtained for an arbitrary ratio between the wavelength of R F and the cavity length. The stimulated emission is also controllable by changing an initial one-photon state and an atomic position.

Roy J. Glauber, Wenyue Hsu

HERBERT WALTHER

Modern methods of laser spectroscopy allow the study of single atoms or ions in an unperturbed environment. This has opened up interesting new experiments, an among them is the detailed study of radiation-atom coupling. This chapter reviews the following two experiments of this type: the single-atom maser and the study of the resonance fluorescence of a single stored ion. The simplest and most fundamental system for studying radiation-matter coupling is a single two-level atom interacting with a single mode of an electromagnetic field in a cavity. There is another aspect of the single-atom maser which is very interesting: the non-classical statistics of the photons in the cavity. The results obtained for the single-atom maser also give a new insight into the statistical properties of masers and lasers. A problem in radiation-matter interaction which has received a lot of interest is resonance fluorescence. The experiments to investigate antibunching in resonance fluorescence have been performed by means of laser-excited collimated atomic beams.