Precision spectroscopy of atomic systems 1 is an invaluable tool for the advancement of our understanding of fundamental interactions and symmetries 2. Recently, highly charged ions (HCI) have been proposed for sensitive tests of physics beyond the Standard Model 2-5 and as candidates for high-accuracy atomic clocks 3,5. However, the implementation of these ideas has been hindered by the parts-per-million level spectroscopic accuracies achieved to date 6-8. Here, we cool a trapped HCI to the lowest reported temperatures, and introduce coherent laser spectroscopy on HCI with an eight orders of magnitude leap in precision. We probe the forbidden optical transition in 40 Ar 13+ at 441 nm using quantum-logic spectroscopy 9,10 and measure both its excited-state lifetime and g-factor. Our work ultimately unlocks the potential of HCI, a large, ubiquitous atomic class, for quantum information processing, novel frequency standards, and highly sensitive tests of fundamental physics, such as searching for dark matter candidates 11 or violations of fundamental symmetries 2. Alike a microscope aimed at the quantum world, laser spectroscopy pursues ever higher resolving power. Every increase in resolution enables deeper insights into the subtle effects that all known fundamental interactions have on the atomic wave function. Advances in optical frequency metrology have dramatically improved resolution in the last three decades 1 , and are making laser spectroscopy an extremely sensitive tool for studying open physics questions such as the nature of dark matter, the strength of parity violation, or a possible violation of Einstein's theory of relativity 2. However, only a few atomic and ionic species are currently within the reach of cutting-edge optical frequency metrology. Expanding this field of exploration to systems with high sensitivity to such effects is therefore crucial. Due to their extreme properties, highly charged ions (HCI) are promising candidates for such fundamental tests. Contributions from special

We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation to |δα/α| < 5 × 10−17 for transients of duration 103 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (≳104 km) objects.

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We experimentally demonstrate the broad tunability of the main features of optical localized structures (LS) in a nonlinear interferometer. By discussing how a single LS depends on the system spatial frequency bandwidth, we show that a modification of its tail leads to the possibility of tuning the interactions between LS pairs, and thus the equilibrium distances at which LS bound states form. This is in agreement with a general theoretical model describing weak interactions of LS in nonlinear dissipative systems.Localization of spatial patterns is a subject of major current interest in the research on nonlinear dissipative dynamical systems. The studies about this topics have naturally followed and sided those dedicated to the formation of temporal and spatial solitons in Hamiltonian systems [1]. Analytical and numerical works have identified several distinct mechanisms leading to structure localization in dissipative systems In particular, optical localized structures (LS), to which we will also refer to as dissipative solitons in the following, are objects of intense research, also in view of possible applications as pixels in devices for information storage or processing. So far, the existence of optical dissipative solitons has been theoretically predicted in many passive [7] and active [8] configurations, and optical LS have been observed in

The power spectral density in Fourier frequency domain, and the different variants of the Allan deviation (ADEV) in dependence on the averaging time are well established tools to analyse the fluctuation properties and frequency instability of an oscillatory signal. It is often supposed that the statistical uncertainty of a measured average frequency is given by the ADEV at a well considered averaging time. However, this approach requires further mathematical justification and refinement, which has already been done regarding the original ADEV for certain noise types. Here we provide the necessary background to use the modified Allan deviation (modADEV) and other two-sample deviations to determine the uncertainty of weighted frequency averages. The type of twosample deviation used to determine the uncertainty depends on the method used for determination of the average. We find that the modADEV, which is connected with Λ-weighted averaging, and the two sample deviation associated to a linear phase regression weighting (parADEV) are in particular advantageous for measurements, in which white phase noise is dominating. Furthermore, we derive a procedure how to minimize the uncertainty of a measurement for a typical combination of white phase and frequency noise by adaptive averaging of the data set with different weighting functions. Finally, some aspects of the theoretical considerations for real-world frequency measurement equipment are discussed.arXiv:1504.00466v3 [physics.data-an]

We investigate the performance of an Er:fiber laser based femtosecond frequency comb for precision metrological applications. Instead of an active stabilization of the comb, the fluctuations of the carrier-envelope offset phase, the repetition phase, and the phase of the beat from a comb line with an optical reference are synchronously detected. We show that these fluctuations can be effectively eliminated by exploiting their known correlation. In our experimental scheme, we utilize two identically constructed frequency combs for the measurement of the fluctuations, rejecting the influence of a shared optical reference. From measuring a white frequency noise level, we demonstrate that a fractional frequency instability better than 1.4 x 10(-14) for 1 s averaging time can be achieved in frequency metrology applications using the Er:fiber based frequency comb.

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A method based on Fourier filtered control signals for stabilization of unstable patterns in a nonlinear optical single feedback system is experimentally realized. The successful stabilization of the homogeneous solution and different stationary periodic patterns far above the pattern forming threshold as well as the elimination of spatiotemporal disorder above a secondary instability has been achieved. The temporal evolution of the control signal verifies the underlying philosophy of noninvasive control that changes only the linear stability of the systems' solution and not the solution itself.