Atom–Field Interaction

Mai-Lin Liang, Yuan Bing

For the Raman interaction between an atom and a two-mode cavity field prepared in the state |01> or |10>, the atom and the field can be disentangled periodically. Such a property of Raman atom-field interaction allows the full entanglement transfer among many atoms and bimodal cavities. In the calculations, each atom is assumed to interact with its own cavity at a different time and so non-identical atoms can be treated conveniently. Entanglement sudden death is discussed too. Though atom-field interaction greatly changes the values of the concurrence for two atoms, configuration of the concurrence is almost not affected. When there is entanglement sudden death, atoms and cavities can still be entangled with one another. However, full entanglement transfer cannot be achieved for such systems with Raman atom-field interaction.

Marlan O. Scully, Muhammad Suhail Zubairy

One of the simplest nontrivial problems involving the atom–field interaction is the coupling of a two-level atom with a single mode of the electromagnetic field. A two-level atom description is valid if the two atomic levels involved are resonant or nearly resonant with the driving field, while all other levels are highly detuned. Under certain realistic approximations, it is possible to reduce this problem to a form which can be solved exactly; allowing essential features of the atom-field interaction to be extracted. In this chapter we present a semiclassical theory of the interaction of a single two-level atom with a single mode of the field in which the atom is treated as a quantum two-level system and the field is treated classically. A fully quantum mechanical theory will be presented in Chapter 6. A two-level atom is formally analogous to a spin-1/2 system with two possible states. In the dipole approximation, when the field wavelength is larger than the atomic size, the atom–field interaction problem is mathematically equivalent to a spin-1/2 particle interacting with a time-dependent magnetic field. Just as the spin-1/2 system undergoes the so-called Rabi oscillations between the spin-up and spin-down states under the action of an oscillating magnetic field, the two-level atom also undergoes optical Rabi oscillations under the action of the driving electromagnetic field. These oscillations are damped if the atomic levels decay. An understanding of this simple model of the atom–field interaction enables us to consider more complicated problems involving an ensemble of atoms interacting with the field.

Miguel Orszag

Y.-T. Cheng, Chin-Hsun Chien, Kaun-Chun Hsieh +14 more

A coherent electromagnetic field can be described by its amplitude, frequency, and phase. All these properties can influence the interaction between the field and an atom. Here we demonstrate the phase shaping of microwaves that are scattered by a superconducting artificial atom coupled to the end of a semi-infinite one-dimensional transmission line. In particular, we input a weak exponentially rising pulse with phase modulation to a transmon qubit. We observe that atom-field interaction can be tuned from a nearly full interaction (interaction efficiency, i.e., amount of the field energy interacting with the atom, of 94.5 %) to effectively no interaction (interaction efficiency of 3.5 %).

Miguel Orszag