4 uous radiation source emitting two multi-mode light beams in different spatial directions, which show bipartite entangle- ment. The desired radiation source consists of the atomic resonance fluorescence of a regular system of several non- interacting atoms. This represents a non-Gaussian source of entangled radiation. For a single atom, entanglement is ob- tained under the same conditions as required for the realiza- tion of squeezing in resonance fluorescence. For a system of N atoms, the situation can be significantly improved, as by in- creasing the number of atoms the entanglement of the emitted light beams is getting more robust against atomic dephasing. As an example, we have estimated the practical limitations of the achievable entanglement for a system of ions in a linear trap. Altogether, the resonance fluorescence of regular atomic systems is a continuous and non-Gaussian source of entangled light, which may open interesting perspectives for various ap- plications in quantum information technology. This work was supported by the Deutsche Forschungsge- meinschaft, SFB 652. ions, due to the distance dependence of the Coulomb interac- tion within the chain of ions, for more details see e.g. [26]. The atomic distances are scaled by an externally controlled length parameter γ , which can be properly adjusted to the number N of trapped ions. One also cannot ignore fluctuations in the positions, as the individual ions are not really fixed due to the uncertainty prin- ciple. Assuming a harmonic potential around each of the equi- librium positions of the ions, the frequency of these harmonic oscillators are nearly equal to the frequency of the trap oscil- lation. This simple assumption overestimates the variances of the atomic positions, since the potential around a given ion rises quickly due to anharmonic effects. Hence the true posi- tion uncertainty can be much smaller than that of an ion in the full trap potential. Nevertheless, we choose this larger value, to effectively account for other possible experimental imper- fections. Using elementary quantum mechanics and statistics, we can approximate the physical limit of the variance of the individual ions as where M is the mass of one of the ions and Q its charge. As- suming for example Q = e and M = 3 . 3309 × 10 − 25 kg and an optical transition wavelength λ = 194 . 2 nm, we ob- tain Δ z ≈ 1 . 014 × 10 − $^{9}$m ( γ λ ) 3 / $^{4}$. This is the situation to be realized with mercury ions, cf. the experiments in [9]. As the variance should be small compared to the transition wave- length to keep statistical averaging effects in the minor µ given by Eq. (9) sufficiently small, we assume a limit of Δ z ≤ 0 . 1 λ . This leads to a maximal value for γ of about 50 λ . Thus we conclude that linear traps would be suited to provide sufficient positioning accuracy of the atoms to realize a continuously ra- diating entangled-light source with regularly arranged atoms for average distances large compared to the wavelength. To verify these theoretical predictions by simulations, we choose the parameter γ in such a way, that for each N the mi- nor µ becomes minimal. The resulting Δ z from Eq. (13) is implemented as an upper bound for a random deviation from the ideal position along the z -axis, variations perpendicular to this axis are assumed to be negligible due to properly cho- sen potentials. The minors have been calculated for the same number of ions and the same parameters as in the ideal case shown in Fig. 1. The calculations for the realistic chain are in reasonable agreement with the idealized results given above. 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