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arXiv:quant-ph/0003105 · IEEE Journal of Quantum Electronics

Quantum fluctuations of a single trapped atom: transient Rabi oscillations and magnetic bistability

H. Schadwinkel, V. Gomer, U. Reiter, B. Ueberholz, D. Meschede

Published Dec 1, 2000• 5 citations
arXivHTMLPDF

Abstract

Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon correlations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: spontaneous magnetic orientation of an atom. These effects can only be observed with a single atom.

DOI
10.1109/3.892554

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Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon correlations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: spontaneous magnetic orientation of an atom. These effects can only be observed with a single atom.
Summary form only given. Photon antibunching is a prime example of quantum fluctuations of the electrodynamic field of resonance fluorescence. In the entangled atom-photon system it is complementally accompanied by transient atomic Rabi oscillations. Polarization resolved resonance fluorescence reveals an analogous phenomenon which can be interpreted as magnetic bistability at the microscopic level. We have subjected a single trapped Cs atom to a 3d-/spl sigma//sup +//spl sigma//sup -/-light field with local linear polarization. An atom in steady state at rest has vanishing magnetization, (m)=0. The observation of very strong anticorrelations for left/right handed photons with a contrast up to 62% and relaxation times of several /spl mu/s can be interpreted as a bistable, spontaneous formation of magnetization in the atom. The detection of the first photon causes projection onto a new state with (m)>0 which creates an unbalanced coupling to the circularly polarized components forming the linearly polarized field. Subsequently the atom is preferentially pumped into a stable stretched m-state. Unidirectional sequential photon absorption is responsible for acceleration (heating), while motion induced optical pumping causes a redistribution of Zeeman sublevels. Relaxation times are compatible with temperatures describing the time scale of atomic motion over a wavelength.
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.
Quantum Rabi oscillation in cavity quantum electrodynamics is at the very heart of the interaction of an atomic system with a single electromagnetic field in a resonator. It has proved a powerful tool to entangle the atom with the field in the case of an empty cavity (vacuum Rabi oscillation). On the other side, as soon as the field is macroscopic, its state seems unaffected and one observes the well-known phenomenon of classical Rabi oscillation which only affects the atomic populations. We propose to experimentally investigate the frontier between those two behaviours, when one has to take into account the fluctations of the photon number. In order to do so, we let interact circular Rydberg atoms with a microwave resonator in which a mesocopic field is injected (a few tens of photons). We observe a strong correlation between specific atomic states and the phase of the injected field, which is measured by a homodyne technique. Those correlations explain in an easy way all the standard features of quantum Rabi oscillations (especially the collapses and revivals). Moreover they allow for the preparation of atom-field entangled state as well as non classical Schroedinger cat like states for the field.
Phase-sensitive detection of resonance fluorescence, i.e., allowing the light emitted from an atom which is undergoing Rabi oscillations in free space to interfere with a coherent local oscillator (LO) beam, has drawn considerable attention throughout the history of quantum optics. Recently, phase-sensitive squeezing spectra for single-atom resonance fluorescence were observed for the first time using strongly-driven long-lived atoms. A measurement of phase-sensitive intensity correlations for this system will be presented. Using physical arguments I will construct the phase-sensitive two-time intensity autocorrelation function, and elucidate the role played by quantum fluctuations in phase-dependent resonance fluorescence.