Helen Freedhoff

VI Spectroscopy in polychromatic fields

Publisher Summary This chapter discusses the spectroscopy in polychromatic fields. The chapter reviews the work performed on spectroscopy with intense polychromatic fields. The chapter focuses on the sub-harmonic resonances and their applications. The sub-harmonic resonances observed in the near-resonance absorption and dispersion profiles of a strong field probing the monochromatically driven, two-level atom sparked renewed interest in these systems. Two principal theoretical methods used to calculate the response of an atom to a polychromatic field are described in the chapter. The chapter reviews the results on the fluorescence, absorption, and Autler-Townes spectra with bichromatic driving fields. The sub-harmonic resonances appear in the absorption and dispersion spectra of an intense field used to probe a monochromatically strongly driven atom—that is, the “strong probe”. The chapter also presents results on more complicated field configurations involving trichromatic and multiple driving fields.

Steady-state resonance fluorescence spectrum of a two-level atom in a cavity

We calculate the steady-state spectrum of resonance fluorescence from a two-level atom coupled to a single cavity mode and driven by a strong, in general off-resonance, external field. In the strong-coupling limit, each Mollow triplet component is split into a multiplet, whose detailed structure depends on the atom–cavity coupling, the cavity and spontaneous emission decay constants, and the photon-number distribution of the cavity mode. The dressed states for this system are identified, and the spectral features are interpreted in terms of transitions among these dressed states. In particular, we find that the central component of the central multiplet can have a strongly subnatural linewidth.

Photon correlations in the fluorescence from a bichromatically driven atom

We study the correlation between photons in the fluorescence light scattered from an atom driven by an intense bichromatic field having one strong and one weak component, with or without the use of frequency filters in front of the photodetectors. Depending on the filters used and on the spectral components selected, we predict signals corresponding either to bunching or to antibunching, and modulations at the driving field Rabi frequencies as well as at their sum and difference. In contrast with the case of monochromatic driving, the antibunching can occur between photons emitted into different (as well as the same) lines of the fluorescence spectrum.

Shift of the subharmonic resonances and suppression of fluorescence in a two-level atom driven by a bichromatic field

We study the behavior of a two-level atom that is driven by a bichromatic field consisting of a strong resonant component and a weaker tunable component. In addition to the splitting of the energy levels (the multiphoton AC Stark effect), we find that the weaker component also shifts the subharmonic resonances, an effect we attribute to a dynamic Stark shift. When the weaker component is tuned to a shifted resonance, no fluorescence occurs at either the frequency of the strong component or the three-photon mixing frequency. Results are obtained with numerical techniques and explained in terms of the dressed-atom model of the system.

Evolution in time of an N-atom system. II. Calculation of the eigenstates

We calculate the energy eigenvalues and eigenstates corresponding to coherent single and multiple excitations of an array of N identical qubits or two-level atoms (TLAs) arranged on the vertices of a regular polygon. We assume only that the coupling occurs via an exchange interaction which depends on the separation between the qubits. We include the interactions between all pairs of qubits, and our results are valid for arbitrary distances relative to the radiation wavelength. To illustrate the usefulness of these states, we plot the distance dependence of the decay rates of the n=2 (biexciton) eigenstates of an array of 4 qubits, and tabulate the biexciton eigenvalues and eigenstates, and absorption frequencies, line widths, and relative intensities for polygons consisting of N=2,...,9 qubits in the long-wavelength limit.

Absorption and dispersion by a driven atom in a cavity

We investigate the absorption and dispersion of a probe field by a two-level atom driven by a strong external field and coupled to a single cavity mode. For moderate atom–field coupling the absorption spectrum contains ultrasharp lines, and the real part of the linear susceptibility changes rapidly at the Mollow sideband frequencies. For large coupling the absorption and dispersion spectra split into multiplets whose structures depend on the photon-number distribution of the cavity field. A large index of refraction accompanied by vanishing absorption is predicted.

Production of Sub-poissonian Light in A Quantum Optical Oscillator

Abstract In this paper we investigate theoretically the behaviour of a quantum optical oscillator, consisting of two-level atoms strongly coupled to a cavity mode, in the optical domain. In contrast with the usual laser theory, we include explicitly the effects of atomic spontaneous emission and of cavity decay in the interaction of the atoms with the cavity field, using a quantum mechanical master equation approach. It is shown that such an oscillator produces sub-Poissonian light with a large degree of noise reduction even for the case when the atom–field coupling constant is only marginally larger than the spontaneous decay rate.

Classical Oscillator Model for Electric Quadrupole Transitions

A classical oscillator model for electric quadrupole transitions is presented, analogous to the Lorentz oscillator model for electric dipole transitions. The model allows one to describe classically the processes of spontaneous emission, scattering, and absorption, taking into account the force of radiative reaction. Transition probabilities, spectra, and the dielectric dyadic of a material due to quadrupole transitions are calculated. All quantities agree completely with the corresponding quantities obtained quantum mechanically.

Spectrum of the one-atom dressed-state oscillator

Abstract The spectrum is calculated of the one-atom dressed-state oscillator, deriving analytical expressions for the spectrum of the cavity field for both moderate and strong atom-cavity coupling. The linewidth is found to be very sharp in the moderate coupling regime, becoming broader with larger coupling and eventually even splitting into a multiplet.

Cooperative Atomic Effects in Two-Photon Processes

The subject of cooperative radiative transitions by a system of two or more identical atoms (or molecules) has received considerable attention over the years, beginning with an initial study by Dicke 1. Many authors since have dealt with coherent single-quantum electric-dipole excitations of systems of two 2,3 or more 3,4 atoms. The effects of the atomic interaction include in general the splitting of each atomic energy level into a number of sublevels, the shift of each sublevel from the single-atom energy, and a change in the lifetime of each sublevel from the single-atom radiative lifetime.