Intensity-intensity correlations as a probe of interferences - under conditions of none in the intensity

The different behaviour of first order interferences and second order correlations are investigated for the case of two coherently excited atoms. For intensity measurements this problem is equivalent to Young's double slit experiment and was investigated in an experiment by Eichmann et al. [Phys. Rev. Lett. 70, 2359 (1993)] and later analyzed in detail by Itano et al. [Phys. Rev. A 57, 4176 (1998)]. Our results show that in cases where the intensity interferences disappear the intensity-intensity correlations can display an interference pattern with a visibility of up to 100%. The contrast depends on the polarization selected for the detection and is independent of the strength of the driving field. The nonclassical nature of the calculated intensity-intensity correlations is also discussed.Comment: 14 pages, 2 figure

Quanteneffekte gespeicherter Ionen

Die Arbeit behandelt Quanteneffekte gespeicherter Ionen. Dabei werden zum einen Effekte behandelt, die aus der Wechselwirkung zwischen Ion und Lichtfeld enstehen, zum anderen aber auch Effekte, welche der Wechselwirkung mehererer Ionen enspringen. Bei den Effekten einzelner Ionen wird die Modifikation der Lamb-Shift unter modifizierten Randbedingungen untersucht, wobei eine theoretische Erweiterung zu den bisherigen Ansätzen gefunden wurde. Der Übergang zwischen Coherent-Population-Trapping und Autler-Townes- Splitting wird ebenso betrachtet, wobei eine scharfe mathematische zwischen den jeweiligen Regimes ermittelt werden konnte. Im weiteren Verlauf der Arbeit, werden Wechselwirkung zwischen 2 gespeicherten Ionen betrachtet. Es konnte gezeigt werden, dass zum Nachweis der Dipol-Dipol-Wechselwirkung die individuelles Detektion der Quantensprünge der einzelnen Ionen erforderlich ist. Jede andere Form der Detektion ist wegen des Quanten-Zeno-Effekts dafür nicht geeignet. Es konnten aber auch Quanteninterferenzen zwischen 2 nichtwechselwirkenden Ionen nachgewiesen werden, welche auf der Verschränkung der Ionen durch ein Messereignis beruhen. Diese manifestieren sich in den Photonenkorrelationsfunktionen des von den Ionen emittierten Lichts. Diese Betrachtungen werden auch auf Ionenketten äquidistanter Ionen ausgedehnt

Magnetyczne własności szeregu związków międzymetalicznych Ce₅MGe₂ i Ce₂M₃Ge, gdzie M jest metalem d-elektronowym

The aim of my doctoral thesis was comprehensive research on new intermetallic compounds Ce₅MGe₂, where M is a metal with partial occupied 3d-, 4d- or 5d-electron shell. Only crystal structure was known for these compounds, while their physical properties defining the ground state of the system have not been studied so far. In this work, a several compounds of Ce₅MGe₂ were obtained, their magnetic properties, specific heat, electric transport and the electronic structure (ab initio calculations and XPS experiment) was investigated. The magnetic, thermal and electron transport properties for the series of Ce₅MGe₂ compounds have been systematized on the basis of their electronic structure, dominated by M and showed a complex magnetic structure of these compounds. Compounds were obtained in the form of polycrystalline Ce₅MGe₂ samples for M = Ru, Rh, Pd Ag and Ce₂Rh₃Ge₂ by arc melting. The crystal structure was examined by X-ray diffraction and the results were developed using the Rietveld method. The electron structure was investigated by XPS Photoelectric Spectroscopy. Magnetic measurements were performed using SQUID and PPMS magnetometer in the fields range up to 7 T. Electrical resistance, thermal conductivity and specific heat were investigated using a PPMS magnetometer. Calculations of the electronic structure were also performed using the available codes

Cooperative fluorescence effects for dipole-dipole interacting systems with experimentally relevant level configurations

The mutual dipole-dipole interaction of atoms in a trap can affect their fluorescence. Extremely large effects were reported for double jumps between different intensity periods in experiments with two and three Ba^+ ions for distances in the range of about ten wave lengths of the strong transition while no effects were observed for Hg^+ at 15 wave lengths. In this theoretical paper we study this question for configurations with three and four levels which model those of Hg^+ and Ba^+, respectively. For two systems in the Hg^+ configuration we find cooperative effects of up to 30% for distances around one or two wave lengths, about 5% around ten wave lengths, and, for larger distances in agreement with experiments, practically none. This is similar for two V systems. However, for two four-level configurations, which model two Ba^+ ions, cooperative effects are practically absent, and this latter result is at odds with the experimental findings for Ba^+.Comment: 9 pages, 5 figures, RevTeX4, to be published in Phys. Rev.

Monitoring the Dipole-Dipole Interaction via Quantum Jumps of Individual Atoms

The emission characteristics in the fluorescence of two laser-driven dipole-dipole-interacting three level atoms is investigated. When the light from both atoms is detected separately a correlation of the emission processes is observed in dependence of the dipole-dipole interaction. This opens the possibility to investigate the dipole-dipole interaction through the emission behavior. We present Monte-Carlo simulations which are in good agreement with the analytic solutions

Inhibition of cooperative quantum jumps due to fast spontaneous decay

A Quantum Monte Carlo wave function approach is used to rule out the possibility of cooperative effects in the quantum jump statistics of adjacent three-level ions of the type discussed in a series of experiments and theoretical investigations. By deriving analytical results and examining quantum jumps in various subspaces, we track this outcome to the fact that a fast spontaneous decay inhibits dipole-dipole-induced entanglement between the ions developing on a much slower time scale. This inhibition is demonstrated even for weak pumping of the fast transition. The Quantum Monte Carlo calculation thus sheds new light on the controversy arising from the findings of two recent conflicting experiments by Block et al. (Eur. Phys. J. D, 7 (1999) 461) and Donald et al. (Europhys. Lett., 51 (2000) 388)

Polarization-correlated photon pairs from a single ion

In the fluorescence light of a single atom, the probability for emission of a photon with certain polarization depends on the polarization of the photon emitted immediately before it. Here correlations of such kind are investigated with a single trapped calcium ion by means of second order correlation functions. A theoretical model is developed and fitted to the experimental data, which show 91% probability for the emission of polarization-correlated photon pairs within 24 ns.Comment: 8 pages, 9 figure

Double scattering of intense laser light by two atoms

This paper analyzes coherent backscattering of intense laser light by two randomly placed distant atoms. Starting from the general two-atom master equation, we analytically derive the elastic and inelastic background and interference components of the double scattering spectrum. By expressing the final results in terms of single-atom observables, the two-atom problem is shown to be equivalent to a description in terms of single atoms under bichromatic driving.Comment: 15 pages, 3 figure

The intensity correlation function of "blinking" quantum systems

Explicit expressions are determined for the photon correlation function of ``blinking'' quantum systems, i.e. systems with different types of fluorescent periods. These expressions can be used for a fit to experimental data and for obtaining system parameters therefrom. For two dipole-dipole interacting $V$ systems the dependence on the dipole coupling constant is explicitly given and shown to be particularly pronounced if the strong driving is reduced. We propose to use this for an experimental verification of the dipole-dipole interaction.Comment: 12 pages, 5 figures, uses iopams.st

Nonclassical Interference Effects In The Radiation From Coherently Driven Uncorrelated Atoms

We demonstrate the existence of new nonclassical correlations in the radiation of two atoms, which are coherently driven by a continuous laser source. The photon-photon-correlations of the fluorescence light show a spatial interferene pattern not present in a classical treatment. A feature of the new phenomenon is, that bunched and antibunched light is emitted in different spatial directions. The calculations are performed analytically. It is pointed out, that the correlations are induced by state reduction due to the measurement process when the detection of the photons does not distinguish between the atoms. It is interesting to note, that the phenomena show up even without any interatomic interaction.Comment: 4 pages, 6 Figure