Stig Stenholm

Quantum theory of electromagnetic fields interacting with atoms and molecules

Abstract This paper reviews the recent achievements in nonrelativistic quantum electrodynamics, especially nonlinear and coherent phenomena. The general properties of coupled radiation and matter are presented within simple models in section 1. The following sections treat in some detail three main aspects of the system and can be read independently of each other. Section 2 discusses some experiments with long-wave-length radiation (r.f.) and atoms. Section 3 presents the quantum theory of a laser and the ensuing photon distributions. Section 4 treats the case of strongly correlated emission of radiation called superradiance. The use of statistical ensembles is briefly discussed in Appendix A, whereas Appendices B, C and D present some technical details of the text.

Quantum Approach to Informatics

Preface. 1. Introduction. 2. Quantum Theory. 3. Quantum Communication and Information. 4. Quantum Computing. 5. Physical Realization of Quantum Information Processing. References. Index.

Simultaneous measurement of conjugate variables

Abstract This paper investigates the possibility to extract optimum information about the momentum and position variables of a quantum mechanical system. For the observation we use a pair of independent detectors, which contribute their own noise to the recorded result. In the optimal case the setup measures the Q-distribution leading to antinormally ordered expectation values. The class of initial detector states to be used is discussed, and the relation to measurement theory is elucidated. The paper summarizes and unifies earlier works by Husimi, Arthurs, and Kelly and Braunstein, Caves and Milburn. A realization in quantum optics is suggested.

Velocity tuned resonances as multi-doppleron processes

Abstract We consider multi-photon processes for a Doppler broadened two-level system. Alternative absorption and emission from two oppositely travelling waves is interpreted as a multi-quantum absorption (or emission) process with quanta h kv . These are called Dopplerons and the analogy with the RF work is established. The calculations also display a resonance caused by slow atoms.

Theoretical foundations of laser spectroscopy

Abstract This paper reviews the use of density matrix methods for nonlinear spectroscopy. It is argued that the two main characteristics of spectroscopy in the optical regime are: spontaneous emission and mechanical effects, i.e. Doppler shifts, recoil effects and light pressure. After surveying the fundamentals of light-matter interaction in section 2, we define the density matrix in section 3. The relationship between classical and quantum descriptions is discussed. Section 4 presents the main features of saturation spectroscopy with lasers. This is the theory for much of optical nonlinear spectroscopy. Section 5 discusses spontaneous emission including resonance fluorescence in a strong field. Section 6 discusses light pressure and the possibilities to manipulate the atomic velocity distribution, trap atoms in optical fields and selectively handle small numbers of atoms. The parts of the review are interconnected and develop the theory from a unified point of view.

Broad band resonant light pressure

This paper treats the mechanical pressure of resonant light acting on a two-level system, where the degenerate magnetic sublevels are taken into account. The theory is developed with arbitrary relations between the quantization axis and the propagation and polarization of the light. Rate terms are obtained both for spontaneous and induced transitions; the requirements of incoherence put restrictions on the possible geometries of the experiment. The rate equations are restricted to motion along a light beam only; this one-dimensional case is simpler to handle. For small recoil velocities a Fokker-Planck equation is derived, and an adiabatic elimination procedure enables us to derive an equation for the velocity distribution of the total population. The assumptions and approximations are formulated and discussed.

Properties of stimulated Raman adiabatic passage with intermediate-level detuning

Abstract We analyse the effect of the intermediate-level detuning on the efficiency of the stimulated Raman adiabatic passage process in three-level systems. We present an exactly solvable analytic model, involving smooth delayed pulses, as well as numerical results and an analytic approximation for Gaussian pulses. Both types of pulses demonstrate that for fixed pulse strengths, the transfer efficiency is adversely affected as the intermediate-level detuning increases because of the deteriorating adiabaticity and eventually vanishes for very large detuning. It is shown that the width of the detuning range, over which the transfer efficiency remains high, is proportional to the squared pulse area. A simple analysis suggests that this feature should be generally valid for any smooth delayed pulses.

Single-particle theory of the free-electron laser in a moving frame

We give a summary of the theory of a single electron involved in free-electron laser (FEL) operation. We use the method of transformation to a predetermined moving frame where the wiggler-laser scattering process is elastic. In this paper, we discuss the classical and quantum dynamics of such an electron and evaluate perturbatively the lowest order FEL behavior from the classical pendulum equation. The presentation is tutorial throughout and stresses analytic results and physically significant dimensionless parameters. No results are included for the dynamic evolution of the light during the laser action.

Quantum description of free electrons in the laser

Abstract The fully quantum mechanical theory of the free electron laser is formulated in the moving frame introduced by the authors. The laser and wiggler fields are taken to be at their classical limit and quantum effects of the electron motion are considered. The Schrodinger equation is written down and solved for the unsaturated gain and momentum distribution. The results are found to be closely related to the corresponding expressions from a fully classical theory.

Heating or cooling collisionally aided fluorescence

Abstract Collisionally aided redistribution of scattered laser light is suggested as a method to cool or heat gaseous samples. The efficiency is evaluated and restricting conditions are considered. Some potential applications are given.