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

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)

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

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

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

Quantum Coherence in a Single Ion due to strong Excitation of a metastable Transition

We consider pump-probe spectroscopy of a single ion with a highly metastable (probe) clock transition which is monitored by using the quantum jump technique. For a weak clock laser we obtain the well known Autler-Townes splitting. For stronger powers of the clock laser we demonstrate the transition to a new regime. The two regimes are distinguished by the transition of two complex eigenvalues to purely imaginary ones which can be very different in magnitude. The transition is controlled by the power of the clock laser. For pump on resonance we present simple analytical expressions for various linewidths and line positions.Comment: 6 figures. accepted for publication in PR

Quantitative conditional quantum erasure in two-atom resonance fluorescence

We present a conditional quantum eraser which erases the a priori knowledge or the predictability of the path a photon takes in a Young-type double-slit experiment with two fluorescent four-level atoms. This erasure violates a recently derived erasure relation which must be satisfied for a conventional, unconditional quantum eraser that aims to find an optimal sorting of the system into subensembles with particularly large fringe visibilities. The conditional quantum eraser employs an interaction-free, partial which-way measurement which not only sorts the system into optimal subsystems with large visibility but also selects the appropriate subsystem with the maximum possible visibility. We explain how the erasure relation can be violated under these circumstances.Comment: Revtex4, 12pages, 4 eps figures, replaced with published version, changes in Sec. 3, to appear in Physical Review

Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings

Within the framework of quantization of the macroscopic electromagnetic field, equations of motion and an effective Hamiltonian for treating both the resonant dipole-dipole interaction between two-level atoms and the resonant atom-field interaction are derived, which can suitably be used for studying the influence of arbitrary dispersing and absorbing material surroundings on these interactions. The theory is applied to the study of the transient behavior of two atoms that initially share a single excitation, with special emphasis on the role of the two competing processes of virtual and real photon exchange in the energy transfer between the atoms. In particular, it is shown that for weak atom-field interaction there is a time window, where the energy transfer follows a rate regime of the type obtained by ordinary second-order perturbation theory. Finally, the resonant dipole-dipole interaction is shown to give rise to a doublet spectrum of the emitted light for weak atom-field interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE